Biodegradable and redox-responsive chitosan/poly(L-aspartic acid) submicron capsules for transmucosal delivery of proteins and peptides

Oromucosal delivery of macromolecules: Challenges and recent developments to improve bioavailability

Owing to their biological diversity, high potency, good tolerability, low immunogenicity, site-specific activity, and great efficacy, macromolecular drugs (i.e., proteins and peptides, antibodies, hormones, nucleic acids, vaccines, etc.) are extensively used as diagnostics, prophylactics, and therapeutics in various diseases. To overcome drawbacks associated with parenteral (invasive) delivery of macromolecules as well as to preserve their therapeutic integrity, oromucosal route (sublingual and buccal) has been proven efficient alternate port of delivery. This review aims to summarize challenges associated with oromucosal route and overtime developments in conventional delivery systems with special emphasis on most recent delivery strategies. Over the past few decades, significant efforts have been made for improving the oromucosal absorption of macromolecules by employing chemical penetration enhancers (CPE), enzyme inhibitors, chemical modification of drug structure (i.e., lipidation, PEGylation, etc.), and mucoadhesive materials in the form of buccal tablets, films (or patches), sprays, fast disintegrating tablets, and microneedles. Adaptation of adjunct strategies (e.g., iontophoresis in conjunction with CPE) has shown significant improvement in oromucosal absorption of macromolecules; however, these approaches were also associated with many drawbacks. To overcome these shortcomings and to further improve therapeutic outcomes, specialized delivery devices called "hybrid nanosystems" have been designed in recent times. This newer intervention showed promising potential for promoting oromucosal absorption and absolute bioavailability of macromolecules along with improved thermostability (cold chain free storage), enabling self-administration, site-specific activity, improving therapeutic efficacy and patient compliance. We anticipate that tailoring of hybrid nanosystems to clinical trials as well as establishing their short- and long-term safety profile would substantiate their therapeutic value as pharmaceutical devices for oromucosal delivery of macromolecules.

Self-Assembled Nanosized Vehicles from Amino Acid-Based Amphiphilic Polymers with Pendent Carboxyl Groups for Efficient Drug Delivery

Developing safe and efficient delivery vehicles for chemotherapeutic drugs has been a long-standing demanding. Amino acid-based polymers are promising candidates to address this challenge due to their excellent biocompatibility and biodegradation. Herein, a series of well-defined amphiphilic block copolymers were prepared by PET-RAFT polymerization of N-acryloyl amino acid monomers. By altering monomer types and the block ratio of the copolymers, the copolymers self-assembled into nanostructures with various morphologies, including spheres, rod-like, fibers, and lamellae via hydrophobic and hydrogen bonding interactions. Significantly, the nanoparticles (NPs) assembled from amphiphilic block copolymers poly(N-acryloyl-valine)-b-poly(N-acryloyl-aspartic acid) (PV-b-PD) displayed an appealing cargo loading efficiency (21.8-32.6%) for a broad range of drugs (paclitaxel, doxorubicin (DOX), cisplatin, etc.) due to strong interactions. The DOX-loaded PV-b-PD NPs exhibited rapid cellular uptake (within 1 min) and a great therapeutic performance. These drug delivery systems provide new insights for regulating the controlled morphologies and improving the efficiency of drug delivery.

Poly(amino acid)s-based star AIEgens for cell uptake with pH-response and chiral difference

Chiral aggregation-induced emission luminogens (AIEgens) are the new-generation chiral sensors that regulate chiral signals from the molecular level to the macroscopic assembly. Expanding applications of chiral AIEgens and in-depth understanding of their chiral recognition in biological systems are meaningful. Herein, two star chiral AIEgens, consisting of tetraphenylethene (TPE) as core and poly(N-acryloyl-L(D) valine) (PLV or PDV) as arms, were precisely synthesized via atom transfer radical polymerization (ATRP) technique and named TPE-PLV and TPE-PDV. They possessed typical AIE characteristics and exhibited an increase in concentration-dependent fluorescence intensity. The two AIEgens were pH-responsive and had strong AIE-related emission in acidic solution. Importantly, AIEgens can enter the living cells by ATP dependent endocytosis, then light them up. The interactions between the AIEgens and living human hepatocarcinoma (HepG2) cells revealed that the internalization process of TPE-PLV and TPE-PDV was both chiral-dependent and pH-responsive. This novel strategy for synthesizing poly(amino acid)s functionalized AIEgens could inspire the development of promising fluorescent materials with chirality.

Nanoscale cationic micelles of amphiphilic copolymers based on star-shaped PLGA and PEI cross-linked PEG for protein delivery application

To enhance the bioavailability of protein therapeutants and improve the stability of storage and delivery, a series of branched amphiphilic block copolymers consisting of cholic acid (CA) initiated poly(D,L-lactide-co-glycolide) (CA-PLGA) and water-soluble polyethyleneimine cross-linked polyethylene glycol (PEI-PEG) denoted as CA-PLGA-b-(PEI-PEG) were synthesized and characterized. CA-PLGA-b-(PEI-PEG) presented low cytotoxicity by MTT and cck-8 assay. The cationic CA-PLGA-b-(PEI-PEG) micelles (diameter about 100 nm and zeta potential 34-61 mV) were prepared through self-assembly method, and complexed with insulin via electrostatic interaction to obtain nanoscale micelle/insulin complexes. The micelle/insulin complexes-loaded CA-PLGA microspheres (MIC-MS, 10.4 ± 3.85 μm) were manufactured by employing a double emulsion (W₁/O/W₂) method. The in vitro insulin release behavior and in vivo hypoglycaemic effect of MIC-MS on streptozotocin (STZ) induced diabetic rats were compared with those of the insulin-loaded CA-PLGA microspheres (INS-MS, 7.8 ± 2.57 μm). The initial burst in vitro release of MIC-MS was markedly lower than that of INS-MS (P < 0.01), and the pharmacological availability of MIC-MS via subcutaneous administration was 148.9% relative to INS-MS. Therefore, the cationic CA-PLGA-b-(PEI-PEG) micelles can effectively increase the bioavailability of insulin in CA-PLGA microspheres and can be considered as a potential protein carrier.

Rapid and label-free detection of Brucella melitensis in milk and milk products using an aptasensor

In this work, a novel quartz crystal microbalance (QCM) aptasensor is designed for the diagnosis of Brucella melitensis bacteria, which affects the Mediterranean fever (brucellosis) from the zoonotic diseases that are very common in the Middle East Countries. The method is based on the selection of B. melitensis bacterium from solutions using B. melitensis specific binding aptamer (Apt) attached magnetic nanoparticles. The surface of the magnetic nanoparticles (i.e.,Fe₃O₄) was modified by 3-aminopropyltriethoxysilane (APTES) and then grafted with a hydrophilic macromonomer poly(ethyleneglycol)-methacrylate (PEG-MA) as a first block polymer and glycidylmethacrylate (GMA) as a second block functional polymer via atom transfer radical polymerization (ATRP) method [Fe₃O₄ @SiO₂ @p(PEG-MA-GMA)], then, the specific binding aptamer was immobilized. The aptamer immobilized magnetic nanoparticles were used for the pre-concentration of the target bacterium, and the same aptamer sequence was also immobilized on the QCM chip and used for the quantitative detection of B. melitensis using QCM aptasensor. The detection limits of the QCM aptasensor were in the range 1.0²-1.0⁷ CFU mL^-1, with recoveries up to 79%. The synthesized [Fe₃O₄ @SiO₂ @p(PEGMA-GMA)] nanoparticles showed a good permanence and high isolation recoveries for the pull down of the target bacterium from food samples, after recycling eight times. The method was successfully applied to target bacterium determinations in milk and milk product samples.

Applying emerging technologies to improve diabetes treatment

Insulin, as the most important drug for the treatment of diabetes, can effectively control the blood glucose concentration in humans. Due to its instability, short half-life, easy denaturation and side effects, the administration way of insulin are limited to subcutaneous injection accompany with poor glucose control and low patient compliance. In recent years, emerging insulin delivery systems have been developed in diabetes research. In this review, a variety of stimuli-responsive insulin delivery systems with their response mechanism and regulation principle are described. Further, the introduction of stem cell transplantation and mobile application based delivery technologies are prudent for the diabetes treatment. This article also discusses the advantages and limitations of current strategies, along with the opportunities and challenges for future insulin therapy.

Systemic Administration of Polyelectrolyte Microcapsules: Where Do They Accumulate and When? In Vivo and Ex Vivo Study

Multilayer capsules of 4 microns in size made of biodegradable polymers and iron oxide magnetite nanoparticles have been injected intravenously into rats. The time-dependent microcapsule distribution in organs was investigated in vivo by magnetic resonance imaging (MRI) and ex vivo by histological examination (HE), atomic absorption spectroscopy (AAS) and electron spin resonance (ESR), as these methods provide information at different stages of microcapsule degradation. The following organs were collected: Kidney, liver, lung, and spleen through 15 min, 1 h, 4 h, 24 h, 14 days, and 30 days after intravenous injections (IVIs) of microcapsules in a saline buffer at a dosage of 2.5 × 10⁸ capsule per kg. The IVI of microcapsules resulted in reversible morphological changes in most of the examined inner organs (kidney, heart, liver, and spleen). The capsules lost their integrity due to degradation over 24 h, and some traces of iron oxide nanoparticles were seen at 7 days in spleen and liver structure. The morphological structure of the tissues was completely restored one month after IVI of microcapsules. Comprehensive analysis of the biodistribution and degradation of entire capsules and magnetite nanoparticles as their components gave us grounds to recommend these composite microcapsules as useful and safe tools for drug delivery applications.

Enzymatically Disulfide-Crosslinked Chitosan/Hyaluronic Acid Layer-by-Layer Self-Assembled Microcapsules for Redox-Responsive Controlled Release of Protein

Disulfide-crosslinked hollow polyelectrolyte microcapsules composed of thiolated chitosan (CS-SH) and hyaluronic acid (HA-SH) were prepared by combining the layer-by-layer (LBL) technique and horseradish peroxidase (HRP)-mediated oxidative cross-linking reaction in mild conditions. FITC-dextran-doped CaCO₃ microspheres were used as template core and removed after LBL depositing CS-SH and HA-SH on the surface. The disulfide-crosslinked (CS/HA) microcapsules were readily fabricated by HRP-mediated oxidative coupling of the thiol groups in CS/HA shell layer in the presence of HRP (10 units/mL) and Tyramine hydrochloride (Tyr, 35 mmol/L). The kinetics of enzymatic disulfide-crosslinking reaction was investigated through the real-time monitoring of the consumption of thiol groups by UV absorption spectra. It found that the formation of disulfide linkages by the enzymatic thiol oxidation reaction showed a gradual acceleration. The disulfide-crosslinked CS/HA hydrogel were rapidly formed in gelation time between approximately 17 and 30 min, which were dependent on the concentrations of HRP and Tyr. The disulfide linkages endowed the microcapsule-enhanced physical stability and low permeability under physiological conditions and redox-responsive degradability in reducing environments. The structural stability of disulfide-crosslinked (CS/HA) microcapsules was visualized by confocal laser scanning microscopy in phosphate-buffered saline containing 5.0 mmol/L dithiothreitol (DTT) to evaluate the redox-responsive disassembly process. Redox-responsive controlled release of encapsulated FITC-dextran from the disulfide-crosslinked (CS/HA) microcapsules were obtained. The release profiles of FITC-dextran could be manipulated by controlling the shell thickness and the concentration of DTT. The conformational stability analyses and more than 94% esterase activity of released bovine serum albumin (BSA) from (CS/HA) microcapsules conformed that the structural integrity and bioactivity were well preserved during the encapsulation and release process. The microcapsules exhibited excellent cytocompatibility for HEK 293 cells up to a concentration of 1.0 mg/mL. The microcapsules efficiently delivered loaded FITC-BSA into HeLa cells and released the protein in the reducing cytosol. This study proposed a novel approach for producing disulfide-crosslinked microcarriers for intracellular delivery and redox-responsive controlled release of protein.

Recent insights in the use of nanocarriers for the oral delivery of bioactive proteins and peptides

Bioactive proteins and peptides have been used with either prophylactic or therapeutic purposes, presenting inherent advantages as high specificity and biocompatibility. Nanocarriers play an important role in the stabilization of proteins and peptides, offering enhanced buccal permeation and protection while crossing the gastrointestinal tract. Moreover, preparation of nanoparticles as oral delivery systems for proteins/peptides may include tailored formulation along with functionalization aiming bioavailability enhancement of carried proteins or peptides. Oral delivery systems, namely buccal delivery systems, represent an interesting alternative route to parenteric delivery systems to carry proteins and peptides, resulting in higher comfort of administration and, therefore, compliance to treatment. This paper outlines an extensive overview of the existing publications on proteins/peptides oral nanocarriers delivery systems, with special focus on buccal route. Manufacturing aspects of most commonly used nanoparticles for oral delivery (e.g. polymeric nanoparticles using synthetic or natural polymers and lipid nanoparticles) advantages and limitations and potential applications of nanoparticles as proteins/peptides delivery systems will also be thoroughly addressed.

Biopolymer microencapsulations of Bacillus thuringiensis crystal preparations for increased stability and resistance to environmental stress

Parasporal crystals synthesized by Bacillus thuringiensis (Bt) have been widely used as microbial pesticides because of their toxicity to the larval stages of specific insects. However, parasporal crystals can be damaged by environmental stresses, such as high temperature, ultraviolet radiation, and desiccation. To reduce environmental susceptibility of parasporal crystals and extend the duration of their activity, we developed a new type of protection by making microcapsules of crystals (MCs). The microcapsules were self-assembled by alternate deposition (layer by layer) of low-cost chitosan and sodium alginate (or sodium carboxymethyl cellulose) on the crystal surface. Crystal toxins (Cry1Ac) were released from microcapsules at pH values above 9.0. Bioassay results demonstrated that microencapsulated preparations had larvicidal toxicity equivalent to the non-encapsulated form. Microencapsuled crystals were protected from environmental stresses such as high temperature and desiccation. The results indicate that microcapsule protection can enhance the efficacy of Bt in pest control, especially to Lepidoptera larvae that have a alkaline midgut.

Bioresorbable polyelectrolytes for smuggling drugs into cells

There is ample evidence that biodegradable polyelectrolyte nanocapsules are multifunctional vehicles which can smuggle drugs into cells, and release them upon endogenous activation. A large number of endogenous stimuli have already been tested in vitro, and in vivo research is escalating. Thus, the interest in the design of intelligent polyelectrolyte multilayer (PEM) drug delivery systems is clear. The need of the hour is a systematic translation of PEM-based drug delivery systems from the lab to clinical studies. Reviews on multifarious stimuli that can trigger the release of drugs from such systems already exist. This review summarizes the available literature, with emphasis on the recent progress in PEM-based drug delivery systems that are receptive in the presence of endogenous stimuli, including enzymes, glucose, glutathione, pH, and temperature, and addresses different active and passive drug targeting strategies. Insights into the current knowledge on the diversified endogenous approaches and methodological challenges may bring inspiration to resolve issues that currently bottleneck the successful implementation of polyelectrolytes into the catalog of third-generation drug delivery systems.

Stimuli-responsive nanomaterials for therapeutic protein delivery

Protein therapeutics have emerged as a significant role in treatment of a broad spectrum of diseases, including cancer, metabolic disorders and autoimmune diseases. The efficacy of protein therapeutics, however, is limited by their instability, immunogenicity and short half-life. In order to overcome these barriers, tremendous efforts have recently been made in developing controlled protein delivery systems. Stimuli-triggered release is an appealing and promising approach for protein delivery and has made protein delivery with both spatiotemporal- and dosage-controlled manners possible. This review surveys recent advances in controlled protein delivery of proteins or peptides using stimuli-responsive nanomaterials. Strategies utilizing both physiological and external stimuli are introduced and discussed.

Enhancing the buccal mucosal delivery of peptide and protein therapeutics

With continuing advances in biotechnology and genetic engineering, there has been a dramatic increase in the availability of new biomacromolecules, such as peptides and proteins that have the potential to ameliorate the symptoms of many poorly-treated diseases. Although most of these macromolecular therapeutics exhibit high potency, their large molecular mass, susceptibility to enzymatic degradation, immunogenicity and tendency to undergo aggregation, adsorption, and denaturation have limited their ability to be administered via the traditional oral route. As a result, alternative noninvasive routes have been investigated for the systemic delivery of these macromolecules, one of which is the buccal mucosa. The buccal mucosa offers a number of advantages over the oral route, making it attractive for the delivery of peptides and proteins. However, the buccal mucosa still exhibits some permeability-limiting properties, and therefore various methods have been explored to enhance the delivery of macromolecules via this route, including the use of chemical penetration enhancers, physical methods, particulate systems and mucoadhesive formulations. The incorporation of anti-aggregating agents in buccal formulations also appears to show promise in other mucosal delivery systems, but has not yet been considered for buccal mucosal drug delivery. This review provides an update on recent approaches that have shown promise in enhancing the buccal mucosal transport of macromolecules, with a major focus on proteins and peptides.

Protein microcapsules: preparation and applications

Liposomes and polymerosomes generally represent the two most widely used carriers for encapsulating compounds, in particular drugs for delivery. While these are well established carriers, recent applications in biomedicine and food industry have necessitated the use of proteins as robust carriers that are stable under extreme acidic and basic conditions, have practically no toxicity and are able to withstand high shear force. This review highlights the different methods for using proteins as encapsulating materials and lists some biomedical applications of the microcapsules. The advantages and limitations in the capsules from the different preparation routes are enumerated.