Penetratin derivative-based nanocomplexes for enhanced intestinal insulin delivery

Peptides as carriers of active ingredients: A review

Bioactive compounds are highly valuable in the fields of food and medicine, but their application is limited due to easy deterioration after oral or skin administration. In recent years, the use of peptides as delivery systems for bioactive compounds has been intensively researched because of their special physicochemical characteristics. Peptides can be assembled using various preparation methods and can form several composite materials such as hydrogels, micelles, emulsions and particles. The composite material properties are determined by peptides, bioactive compounds and the construction methods employed. Herein, this paper provides a comprehensive review of the peptides used for active ingredients delivery, fabrication methods for creating delivery systems, structures, targeting characteristics, functional activities and mechanism of delivery systems, as well as their absorption and metabolism, which provided theoretical basis and reference for further research and development of functional composites.

Eco-friendly chitosan-based nanostructures in diabetes mellitus therapy: Promising bioplatforms with versatile therapeutic perspectives

Nature-derived polymers, or biopolymers, are among the most employed materials for the development of nanocarriers. Chitosan (CS) is derived from the acetylation of chitin, and this biopolymer displays features such as biocompatibility, biodegradability, low toxicity, and ease of modification. CS-based nano-scale delivery systems have been demonstrated to be promising carriers for drug and gene delivery, and they can provide site-specific delivery of cargo. Owing to the high biocompatibility of CS-based nanocarriers, they can be used in the future in clinical trials. On the other hand, diabetes mellitus (DM) is a chronic disease that can develop due to a lack of insulin secretion or insulin sensitivity. Recently, CS-based nanocarriers have been extensively applied for DM therapy. Oral delivery of insulin is the most common use of CS nanoparticles in DM therapy, and they improve the pharmacological bioavailability of insulin. Moreover, CS-based nanostructures with mucoadhesive features can improve oral bioavailability of insulin. CS-based hydrogels have been developed for the sustained release of drugs and the treatment of DM complications such as wound healing. Furthermore, CS-based nanoparticles can mediate delivery of phytochemicals and other therapeutic agents in DM therapy, and they are promising compounds for the treatment of DM complications, including nephropathy, neuropathy, and cardiovascular diseases, among others. The surface modification of nanostructures with CS can improve their properties in terms of drug delivery and release, biocompatibility, and others, causing high attention to these nanocarriers in DM therapy.

Systemic and brain delivery of antidiabetic peptides through nasal administration using cell-penetrating peptides

The intranasal route has emerged as a promising strategy that can direct delivery of drugs into the systemic circulation because the high-vascularized nasal cavity, among other advantages, avoids the hepatic first-pass metabolism. The nose-to-brain pathway provides a non-invasive alternative to other routes for the delivery of macromolecular therapeutics. A great variety of methodologies has been developed to enhance the efficiency of transepithelial translocation of macromolecules. Among these, the use of cell-penetrating peptides (CPPs), short protein transduction domains (PTDs) that facilitate the intracellular transport of various bioactive molecules, has become an area of extensive research in the intranasal delivery of peptides and proteins either to systemic or to brain compartments. Some CPPs have been applied for the delivery of peptide antidiabetics, including insulin and exendin-4, for treating diabetes and Alzheimer's disease. This review highlights the current status of CPP-driven intranasal delivery of peptide drugs and its potential applicability as a universal vehicle in the nasal drug delivery.

Emerging Theranostic Nanomaterials in Diabetes and Its Complications

Diabetes mellitus (DM) refers to a group of metabolic disorders that are characterized by hyperglycemia. Oral subcutaneously administered antidiabetic drugs such as insulin, glipalamide, and metformin can temporarily balance blood sugar levels, however, long-term administration of these therapies is associated with undesirable side effects on the kidney and liver. In addition, due to overproduction of reactive oxygen species and hyperglycemia-induced macrovascular system damage, diabetics have an increased risk of complications. Fortunately, recent advances in nanomaterials have provided new opportunities for diabetes therapy and diagnosis. This review provides a panoramic overview of the current nanomaterials for the detection of diabetic biomarkers and diabetes treatment. Apart from diabetic sensing mechanisms and antidiabetic activities, the applications of these bioengineered nanoparticles for preventing several diabetic complications are elucidated. This review provides an overall perspective in this field, including current challenges and future trends, which may be helpful in informing the development of novel nanomaterials with new functions and properties for diabetes diagnosis and therapy.

Hydrophobic ion-pairing assembled liposomal Rhein with efficient loading for acute pancreatitis treatment

AIM

The present study aimed to develop liposomal Rhein by employing a hydrophobic ion-pairing technique (HIP) for improved pancreatitis therapy.

METHODS

F127 modified liposomal Rhein (F127-RPC-Lip) was prepared using a two-step process consisting of complexation first, followed by a film-ultrasonic dispersion step. The drug-phospholipid interaction was characterised by FT-IR and P-XRD. Particle size and morphology were investigated using DLS and TEM, respectively. Biodistribution and therapeutic efficacy of F127-RPC-Lip were evaluated in a rat model of acute pancreatitis.

RESULTS

F127-RPC-Lip achieved efficient drug encapsulation after complexation with lipids through non-covalent interactions and had an average hydrodynamic diameter of about 141 nm. F127-RPC-Lip demonstrated slower drug release (55.90 ± 3.60%, w/w) than Rhein solution (90.27 ± 5.11%) within 24 h. Compared with Rhein, F127-RPC-Lip exhibited prolonged systemic circulation time, superior drug distribution, and attenuated injury in the pancreas of rats post-injection.

CONCLUSIONS

HIP-assembled liposomes are a promising strategy for Rhein in treating pancreatitis.

Bile acid transporter-mediated oral absorption of insulin via hydrophobic ion-pairing approach

Despite many ongoing and innovative approaches, there are still formidable challenges in the clinical translation of oral peptide drugs into marketable products due to their low absorption and poor bioavailability. Herein, a novel nanocarrier platform was developed that employs a hydrophobic ion-pairing (HIP) of model peptide (insulin) and the anionic bile salt (sodium glycodeoxycholate, SGDC), and markedly improves intestinal absorption via the bile acid pathway. The developed HIP-nanocomplexes (C1 and C2) were optimized, characterized, and in vitro and in vivo evaluation were performed to assess oral efficacy of these system. The optimal molar ratios of C1 and C2-nanocomplexes were 30:1 and 6:1 (SGDC:insulin), respectively. Compared to the insulin solution, the C1 and C2 nanocomplexes significantly enhanced the permeation of insulin across the Caco-2 cell monolayers, with 6.36- and 4.05-fold increases in apparent permeability, respectively. Uptake mechanism studies were conducted using different endocytosis inhibitors and apical sodium-dependent bile acid transporter (ASBT)-transfected MDCK cells, which demonstrated the involvement of the energy-dependent ASBT-mediated active transport. Furthermore, the intrajejunal administration of C1 and C2 resulted in their pharmacological availabilities (PA) being 6.44% and 0.10%, respectively, indicating increased potential for C1, when compared to C2. Similarly, the PA and the relative bioavailability with intrajejunal administration of the C1 were 17.89-fold and 16.82-fold greater than those with intracolonic administration, respectively, confirming better jejunal absorption of C1. Overall, these findings indicate that the HIP-nanocomplexes could be a prominent platform for the effective delivery of peptides with improved intestinal absorption.

Sulfated alginate/polycaprolactone double-emulsion nanoparticles for enhanced delivery of heparin-binding growth factors in wound healing applications

Diabetic foot ulcers (DFUs) that are not effectively treated could lead to partial or complete lower limb amputations. The lack of connective tissue growth factor (CTGF) and insulin-like growth factor (IGF-I) in DFUs results in limited matrix deposition and poor tissue repair. To enhance growth factor (GF) availability in DFUs, heparin (HN)-mimetic alginate sulfate/polycaprolactone (AlgSulf/PCL) double emulsion nanoparticles (NPs) with high affinity and sustained release of CTGF and IGF-I were synthesized. The NPs size, encapsulation efficiency (EE), cytotoxicity, cellular uptake and wound healing capacity in immortalized primary human adult epidermal cells (HaCaT) were assessed. The sonication time and amplitude used for NPs synthesis enabled the production of particles with a minimum of 236 ± 25 nm diameter. Treatment of HaCaT cells with up to 50 μg mL^-1 of NPs showed no cytotoxic effects after 72 h. The highest bovine serum albumin EE (94.6 %, P = 0.028) and lowest burst release were attained with AlgSulf/PCL. Moreover, cells treated with AlgSulf/CTGF (250 ng mL^-1) exhibited the most rapid wound closure compared to controls while maintaining fibronectin synthesis. Double-emulsion NPs based on HN-mimetic AlgSulf represent a novel approach which can significantly enhance diabetic wound healing and can be expanded for applications requiring the delivery of other HN-binding GFs.

Revealing the importance of carrier-cargo association in delivery of insulin and lipidated insulin

Delivery of therapeutic peptides upon oral administration is highly desired and investigations report that the cell-penetrating peptide (CPP) penetratin and its analogues shuffle and penetramax show potential as carriers to enhance insulin delivery. Exploring this, the specific aim of the present study was to understand the impact that their complexation with a lipidated or non-lipidated therapeutic cargo would have on the delivery, to evaluate the effect of differences in membrane interactions in vitro and in vivo, as well as to deduce the mode of action leading to enhanced delivery. Fundamental biophysical aspects were studied by a range of orthogonal methods. Transepithelial permeation of therapeutic peptide was evaluated using the Caco-2 cell culture model supplemented with epithelial integrity measurements, real-time assessment of the carrier peptide effects on cell viability and on mode of action. Pharmacokinetic and pharmacodynamic (PK/PD) parameters were evaluated following intestinal administration to rats and tissue effects were investigated by histology. The biophysical studies revealed complexation of insulin with shuffle and penetramax, but not with penetratin. This corresponded to enhanced transepithelial permeation of insulin, but not of lipidated insulin, when in physical mixture with shuffle or penetramax. The addition of shuffle and penetramax was associated with a lowering of Caco-2 cell monolayer integrity and viability, where the lowering of cell viability was immediate, but reversible. Insulin delivery in rats was enhanced by shuffle and penetramax and accompanied by a 10-20-fold decrease in blood glucose with immediate effect on the intestinal mucosa. In conclusion, shuffle and penetramax, but not penetratin, demonstrated to be potential candidates as carriers for transmucosal delivery of insulin upon oral administration, and their effect depended on association with both cargo and cell membrane. Interestingly, the present study provides novel mechanistic insight that peptide carrier-induced cargo permeation points towards enhancement via the paracellular route in the tight epithelium. This is different from the anticipated belief being that it is the cell-penetrating capability that facilitate transepithelial cargo permeation via a transcellular route.

Accelerating transdermal delivery of insulin by ginsenoside nanoparticles with unique permeability

Diabetes is a metabolic disease caused by insufficient insulin secretion, action or resistance, in which insulin plays an irreplaceable role in the its treatment. However, traditional administration of insulin requires continuous subcutaneous injections, which is accompanied by inevitable pain, local tissue necrosis and hypoglycemia. Herein, a green and safe nanoformulation with unique permeability composed of insulin and ginsenosides is developed for transdermal delivery to reduce above-mentioned side effects. The ginsenosides are self-assembled to form shells to protect insulin from hydrolysis and improve the stability of nanoparticles. The nanoparticles can temporarily permeate into cells in 5 min and promptly excrete from the cell for deeper penetration. The insulin permeation is related to the disorder of stratum corneum lipids caused by ginsenosides. The skin acting as drug depot mantains the nanoparticles released continuously, therefore the body keeps euglycemic for 48 h. Encouraged by its long-lasting and effective transdermal therapy, ginsenosides-based nano-system is expected to deliver other less permeable drugs like proteins and peptides and benefit those who are with chronic diseases that need long-term medication.

Cyclodextrins-Peptides/Proteins Conjugates: Synthesis, Properties and Applications

Cyclodextrins (CDs) are a family of macrocyclic oligosaccharides mostly composed of six, seven, or eight α-D-glucopyranose units with α-1,4-glycosidic bonds to form toroidal structures. The CDs possess a hydrophilic exterior and hydrophobic interior with the ability to form an inclusion complex, especially with hydrophobic molecules. However, most existing studies are about conjugation CDs with peptide/protein focusing on the formation of new systems. The CD-peptide/protein can possess new abilities; particularly, the cavity can be applied in modulation properties of more complexed proteins. Most studies are focused on drug delivery, such as targeted delivery in cell-penetrating peptides or co-delivery. The co-delivery is based mostly on polylysine systems; on the other hand, the CD-peptide allows us to understand biomolecular mechanisms such as fibryllation or stem cell behaviour. Moreover, the CD-proteins are more complexed systems with a focus on targeted therapy; these conjugates might be controllable with various properties due to changes in their stability. Finally, the studies of CD-peptide/protein are promising in biomedical application and provide new possibilities for the conjugation of simple molecules to biomolecules.

β-Cyclodextrin-containing chitosan-oligonucleotide nanoparticles improve insulin bioactivity, gut cellular permeation and glucose consumption

OBJECTIVES

The main objective of the present study was to develop a nanoparticulate drug delivery system that can protect insulin against harsh conditions in the gastrointestinal (GI) tract. The effects of the following employed techniques, including lyophilisation, cross-linking and nanoencapsulation, on the physicochemical properties of the formulation were investigated.

METHODS

We herein developed a nanocarrier via ionotropic gelation by using positively charged chitosan and negatively charged Dz13Scr. The lyophilised nanoparticles with optimal concentrations of tripolyphosphate (cross-linking agent) and β-cyclodextrin (stabilising agent) were characterised by using physical and cellular assays.

KEY FINDINGS

The addition of cryoprotectants (1% sucrose) in lyophilisation improved the stability of nanoparticles, enhanced the encapsulation efficiency, and ameliorated the pre-mature release of insulin at acidic pH. The developed lyophilised nanoparticles did not display any cytotoxic effects in C2C12 and HT-29 cells. Glucose consumption assays showed that the bioactivity of entrapped insulin was maintained post-incubation in the enzymatic medium.

CONCLUSIONS

Freeze-drying with appropriate cryoprotectant could conserve the physiochemical properties of the nanoparticles. The bioactivity of the entrapped insulin was maintained. The prepared nanoparticles could facilitate the permeation of insulin across the GI cell line.

Drug-Encapsulated Cyclodextrin Nanosponges

To date, a number of nanocarriers, either inorganic or organic, have been developed to improve the delivery and therapeutic efficacy of various drugs. Drug delivery systems have attempted to overcome the undesirable pharmacokinetic problems encountered. Among the various nanomaterials that have been designed as potential nanocarriers, cyclodextrin-based polymers are of particular interest in this review.Cyclodextrins (CD) are a class of cyclic glucopyranose oligomers, obtained from starch by enzymatic action, with a characteristic toroidal shape that forms a truncated cone-shaped lipophilic cavity. The main common native cyclodextrins are named α, β, and γ which comprise six, seven, and eight glucopyranose units, respectively. Cyclodextrins have the capability to include compounds whose size and polarity are compatible with those of their cavity.Cyclodextrin-based cross-linked polymers, often referred to as "cyclodextrin nanosponges" (CDNSs), attract great attention from researchers for solving major bioavailability problems such as inadequate solubility, poor dissolution rate, and limited stability of some agents, as well as increasing their effectiveness and decreasing unwanted side effects.Registered patents about this novel system in various fields, different pharmaceutical applications, and classes of drugs encapsulated by CDNSs are detailed. The features outlined make CDNSs a promising platform for the development of innovative and advanced delivery systems.

Role of lipid nanocarriers for enhancing oral absorption and bioavailability of insulin and GLP-1 receptor agonists

Growing demand for insulin and glucagon-like peptide-1 receptor agonists (GLP-1 RA) is observed, considering the progressive nature of diabetes and the potential therapeutic role of peptides in its treatment. However, chronic parenteral administration is responsible for pain and rashes at the site of injection. Oral delivery of insulin and GLP-1 RA promises better patient compliance owing to their ease of administration and reduction in chances of peripheral hypoglycaemia and weight gain. The review article discusses the potential of lipid carriers in combination with different strategies such as absorption enhancers, PEGylation, lipidisation, etc. The lipid nanocarriers improve the membrane permeability and oral bioavailability of high molecular weight peptides. Additionally, the clinical status of different nanocarriers for anti-diabetic peptides is discussed. Previous research on nanocarriers showed significant hypoglycaemic activity and safety in animal studies; however, extrapolation of the same in human subjects is not validated. With the rising global burden of diabetes, the lipid nanocarriers show the potential to revolutionise treatment with oral delivery of insulin and GLP-1 RA.

Fabrication techniques for the preparation of orally administered insulin nanoparticles

The development of orally administered protein drugs is challenging due to their intrinsic unfavourable features, including large molecular size and poor chemical stability, both of which limit gastrointestinal (GI) absorption efficiency. Nanoparticles can overcome the GI barriers effectively and improve the oral bioavailability of proteins in the GI tract. They possess large surface area to volume ratio, and can facilitate the GI absorption of nanoparticles via the paracellular and transcellular routes. Nanoparticles can be prepared by various fabrication techniques that can encapsulate the fragile therapeutic proteins via hydrophobic bonding and electrostatic interaction. A desirable technique should involve minimal harsh conditions and encapsulate therapeutic proteins with preserved functionalities. The current review examines the characteristics of each preparation technique, and illustrates the examples of insulin-loaded nanoparticles that have been developed in each fabrication method. The following techniques, which include nanoprecipitation, hydrophobic conjugation, flash nanocomplexation, double emulsion, ionotropic gelation, and layer-by-layer adsorption, have been used to formulate ligand-modified nanoparticles for targeted delivery of insulin. Other techniques, including reduction, complex coacervation (polyelectrolyte complexation), hydrophobic ion pairing and emulsion solvent diffusion method, and sol-gel technology, were also discussed in the latter part of the review due to their extensive use in fabrication of insulin nanoparticles. This review also discusses the strategies that have been utilised during the formulation process to improve the stability and bioactivity of therapeutic proteins.

Cyclodextrins based delivery systems for macro biomolecules

Macro biomolecules are of vital importance in regulating the biofunctions in organisms, in which proteins (including peptides when mentioned below) and nucleic acids (NAs) are the most important. Therefore, these proteins and NAs can be applied as "drugs" to regulate the biofunctions from abnormal to normal. Either for proteins and NAs, the most challenging thing is to avoid the biodegradation or physicochemical degradation before they reach the targeted location, and then functions as complete functional structures. Hence, appropriate delivery systems are very important which can protect them from these degradations. Cyclodextrins (CDs) based delivery systems achieved mega successes due to their outstanding pharmaceutical properties and there have been several reviews on CDs based small molecule drug delivery systems recently. But for biomolecules, which are getting more and more important for modern therapies, however, there are very few reviews to systematically summarize and analyze the CDs-based macro biomolecules delivery systems, especially for proteins. In this review, there were some of the notable examples were summarized for the macro biomolecules (proteins and NAs) delivery based on CDs. For proteins, this review included insulin, lysozyme, bovine serum albumin (BSA), green fluorescent protein (GFP) and IgG's, etc. deliveries in slow release, stimulating responsive release or targeting release manners. For NAs, this review summarized cationic CD-polymers and CD-cluster monomers as NAs carriers, notably, including the multicomponents targeting CD-based carriers and the virus-like RNA assembly method siRNA carriers.

Increased Carrier Peptide Stability through pH Adjustment Improves Insulin and PTH(1-34) Delivery In Vitro and In Vivo Rather than by Enforced Carrier Peptide-Cargo Complexation

Oral delivery of therapeutic peptides is hampered by their large molecular size and labile nature, thus limiting their permeation across the intestinal epithelium. Promising approaches to overcome the latter include co-administration with carrier peptides. In this study, the cell-penetrating peptide penetratin was employed to investigate effects of co-administration with insulin and the pharmacologically active part of parathyroid hormone (PTH(1-34)) at pH 5, 6.5, and 7.4 with respect to complexation, enzymatic stability, and transepithelial permeation of the therapeutic peptide in vitro and in vivo. Complex formation between insulin or PTH(1-34) and penetratin was pH-dependent. Micron-sized complexes dominated in the samples prepared at pH-values at which penetratin interacts electrostatically with the therapeutic peptide. The association efficiency was more pronounced between insulin and penetratin than between PTH(1-34) and penetratin. Despite the high degree of complexation, penetratin retained its membrane activity when applied to liposomal structures. The enzymatic stability of penetratin during incubation on polarized Caco-2 cell monolayers was pH-dependent with a prolonged half-live determined at pH 5 when compared to pH 6.5 and 7.4. Also, the penetratin-mediated transepithelial permeation of insulin and PTH(1-34) was increased in vitro and in vivo upon lowering the sample pH from 7.4 or 6.5 to 5. Thus, the formation of penetratin-cargo complexes with several molecular entities is not prerequisite for penetratin-mediated transepithelial permeation a therapeutic peptide. Rather, a sample pH, which improves the penetratin stability, appears to optimize the penetratin-mediated transepithelial permeation of insulin and PTH(1-34).

Flash Fabrication of Orally Targeted Nanocomplexes for Improved Transport of Salmon Calcitonin across the Intestine

Salmon calcitonin (sCT) is a potent calcium-regulating peptide hormone and widely applied for the treatment of some bone diseases clinically. However, the therapeutic usefulness of sCT is hindered by the frequent injection required, owing to its short plasma half-life and therapeutic need for a high dose. Oral delivery is a popular modality of administration for patients because of its convenience to self-administration and high patient compliance, while orally administered sCT remains a great challenge currently due to the existence of multiple barriers in the gastrointestinal (GI) tract. Here, we introduced an orally targeted delivery system to increase the transport of sCT across the intestine through both the paracellular permeation route and the bile acid pathway. In this system, sCT-based glycol chitosan-taurocholic acid conjugate (GC-T)/dextran sulfate (DS) ternary nanocomplexes (NC-T) were produced by a flash nanocomplexation (FNC) process in a kinetically controlled mode. The optimized NC-T exhibited well-controlled properties with a uniform and sub-60 nm hydrodynamic diameter, high batch-to-batch reproducibility, good physical or chemical stability, as well as sustained drug release behaviors. The studies revealed that NC-T could effectively improve the intestinal uptake and permeability, owing to its surface functionalization with the taurocholic acid ligand. In the rat model, orally administered NC-T showed an obvious hypocalcemia effect and a relative oral bioavailability of 10.9%. An in vivo assay also demonstrated that NC-T induced no observable side effect after long-term oral administration. As a result, the orally targeted nanocomplex might be a promising candidate for improving the oral transport of therapeutic peptides.

Anionic nanoparticles enable the oral delivery of proteins by enhancing intestinal permeability

The oral delivery of bioactive peptides and proteins is prevented by the intestinal epithelial barrier, in which intercellular tight junction complexes block the uptake of macromolecules. Here we show that anionic nanoparticles induce tight junction relaxation, increasing intestinal permeability and enabling the oral delivery of proteins. This permeation-enhancing effect is a function of nanoparticle size and charge, with smaller (≤ 200 nm) and more negative particles (such as silica) conferring enhanced permeability. In healthy mice, silica nanoparticles enabled the oral delivery of insulin and exenatide, with 10 U kg-1 orally delivered insulin sustaining hypoglycaemia for a few hours longer than a 1 U kg-1 dose of subcutaneously injected insulin. In healthy, hyperglycaemic and diabetic mice, the oral delivery of 10 U kg-1 insulin led to a dose-adjusted bioactivity of, respectively, 35%, 29% and 23% that of the subcutaneous injection of 1 U kg-1 insulin. The permeation-enhancing effect of the nanoparticles was reversible, non-toxic, and attributable to the binding to integrins on the surface of epithelial cells.

Engineering drug delivery systems to overcome mucosal barriers for immunotherapy and vaccination

Mucosal surfaces protect our bodies from pathogens and external irritants using a system of biological barriers. Overcoming these barriers is a significant drug delivery challenge, particularly for immunotherapies that aim to modulate the local immune response. Reaching local lymphoid tissues and draining lymph nodes (LNs) requires crossing the mucus mesh, mucosal epithelium, and either targeting M cells covering lymphoid tissues or utilizing lymphatic transport that shuttles molecules and particulates from the periphery to the LN. We first highlight the barrier properties of mucus and mucosal epithelium, and the function of the mucosal immune system. We then dive into existing drug delivery technologies that have been engineered to overcome each of these barriers. We particularly focus on novel strategies for targeting lymphoid tissues, which has been shown to enhance immunotherapies and vaccinations, via directly targeting LNs, lymphatic vessels, and M cells that transport samples of mucosal content to the lymphoid tissues.

Bio-nanotechnological advancement of orally administered insulin nanoparticles: Comprehensive review of experimental design for physicochemical characterization

Therapeutic proteins are labile macromolecules that are prone to degradation during production, freeze-drying and storage. Recent studies showed that nanoparticles can enhance the stability and oral bioavailability of encapsulated proteins. Several conventional approaches (enzyme inhibitors, mucoadhesive polymers) and novel strategies (surface modification, ligand conjugation, flash nano-complexation, stimuli-responsive drug delivery systems) have been employed to improve the physiochemical properties of nanoparticles such as size, zeta potential, morphology, polydispersity index, drug release kinetics and cell-targeting capacity. However, clinical translation of protein-based nanoparticle is limited due to poor experimental design, protocol non-compliance and instrumentation set-up that do not reflect the physiological conditions, resulting in difficulties in mass production of nanoparticles and waste in research funding. In order to address the above concerns, we conducted a comprehensive review to examine the experimental designs and conditions for physical characterization of protein-based nanoparticles. Reliable and robust characterization is essential to verify the cellular interactions and therapeutic potential of protein-based nanoparticles. Importantly, there are a number of crucial factors, which include sample treatment, analytical method, dispersants, sampling grid, staining, quantification parameters, temperature, drug concentration and research materials, should be taken into careful consideration. Variations in research protocol and unreasonable conditions that are used in optimization of pharmaceutical formulations can have great impact in result interpretation. Last but not least, we reviewed all novel instrumentations and assays that are available to examine mucus diffusion capacity, stability and bioactivity of protein-based nanoparticles. These include circular dichroism, fourier transform infrared spectroscopy, X-ray diffractogram, UV spectroscopy, differential scanning calorimetry, fluorescence spectrum, Förster resonance energy transfer, NMR spectroscopy, Raman spectroscopy, cellular assays and animal models.

Dimension-shifting multifunctional biocompatible nanocomposites

A facile method to prepare dimension-shifting biocompatible multifunctional nanocomposites is described. The design is based on magnetic - and electrostatic - induced transitions from the dispersed state to the assembled state of zero-dimensional nanoparticles, resulting in dimension conversion.

Engineering Polymer-Binding Bispecific Antibodies for Enhanced Pretargeted Delivery of Nanoparticles to Mucus-Covered Epithelium

Mucus represents a major barrier to sustained and targeted drug delivery to mucosal epithelium. Ideal drug carriers should not only rapidly diffuse across mucus, but also bind the epithelium. Unfortunately, ligand-conjugated particles often exhibit poor penetration across mucus. In this work, we explored a two-step "pretargeting" approach through engineering a bispecific antibody that binds both cell-surface ICAM-1 and polyethylene glycol (PEG) on the surface of nanoparticles, thereby effectively decoupling cell targeting from particle design and formulation. When tested in a mucus-coated Caco-2 culture model that mimics the physiological process of mucus clearance, pretargeting increased the amount of PEGylated particles binding to cells by around 2-fold or more compared to either non-targeted or actively targeted PEGylated particles. Pretargeting also markedly enhanced particle retention in mouse intestinal tissues. Our work underscores pretargeting as a promising strategy to improve the delivery of therapeutics to mucosal surfaces.

Impact of mucoadhesive polymeric nanoparticulate systems on oral bioavailability of a macromolecular model drug

Nanoparticles (NP) only different in mucoadhesivity are compared for impact on drug oral bioavailability. Two polymeric NP types based on quaternary ammonium-chitosan (NP QA-Ch) and S-protected thiolated derivative thereof (NP QA-Ch-S-pro), respectively, containing the macromolecular drug model, FD4, were prepared by crosslinking each polymer with reduced MW hyaluronic acid. The structure of basic polymers was determined by H¹NMR analysis. NP were similar in size (371 ± 38 vs. 376 ± 82 nm); polydispersity index (0.39 ± 0.08 vs. 0.41 ± 0.10); zeta potential (13.4 ± 0.9 vs. 11.9 ± 1.2 mV); reversible interactions with drug (bound drug, 67 vs. 66%); encapsulation efficiency (23 ± 5 vs. 23 ± 8%); release properties (15% released in 15 h in both cases); and apparent permeation across excised rat intestine (P_app, 8.8 ± 0.8 vs. 10 ± 1 cm/s). Then the differences in NP transport ratio through mucus (TR, 0.75 vs. 0.37) and adhesion to excised rat intestinal mucosa (adsorbed fraction, 23 ± 3 vs. 45 ± 2%) were ascribed to higher mucoadhesivity of NP QA-Ch-S-pro compared to NP QA-Ch. This directly influenced drug oral bioavailability in rats (T_max, 1 vs. 2 h; AUC, 1.7 ± 0.3 vs. 2.9 ± 0.4 μg/mL min, for NP QA-Ch and NP QA-Ch-S-pro, respectively). Mucoadhesivity increases drug bioavailability by retaining NP at its absorption site and opposing its transit down the GI tract. Data on drug accumulation in rat liver allows the assertion that NP is absorbed by transcytosis across intestinal epithelium and transported from blood into liver by Kuppfer cells.

Oral delivery of anti-diabetes therapeutics using cell penetrating and transcytosing peptide strategies

Oral delivery of insulin and other anti-diabetic peptides is inhibited by low intestinal absorption caused by the poor permeability across cellular membranes and the susceptibility to enzymatic degradation in the gastrointestinal tract. Cell-penetrating peptides (CPPs) have been investigated for a number of years as oral absorption enhancers for hydrophilic macromolecules by electrostatic or covalent conjugation on in conjunction with nanotechnology. Endogenous cellular uptake mechanisms present in the intestine can be exploited by engineering peptide conjugates that transcytose; entering cells by endocytosis and leaving by exocytosis. Efficiently delivering hydrophilic and sensitive peptide drugs to safely transverse the digestive barrier with no effect on gut physiology using remains a key driver for formulation research. Here we review the use of CPP and transcytosis peptide approaches, their modification and use in delivering anti-diabetic peptides (with the primary example of Insulin and engineered homologues) by direct oral administration to treat diabetes and associated metabolic disorders.

Study on orally delivered paclitaxel nanocrystals: modification, characterization and activity in the gastrointestinal tract

Drug nanocrystals (NCs) can improve the solubility and bioavailability of insoluble drugs for oral administration. However, the biocompatibility and mechanisms of transmittance of drug NCs through the intestinal epithelial tissue are still not well understood. In this work, the physico-chemical properties and interactions with biomolecules in oral delivery pathways, as well as the transmittance through mimical intestinal epithelial cells, of NCs of paclitaxel (PTX) are investigated. PTX was previously demonstrated to be an effective anti-cancer drug. It is found that maximum 1% (w/v) poly(styrenesulfonate) is sufficient to keep PTX NCs monodisperse in varied biological environments and presents no significant interaction with extracellular biomolecules for at least 24 h. The concentration of PTX NCs is kept carefully controlled to avoid serious toxicity to cells (10 µg ml^-1 in our experiments but this also depends on NC size). The transmittance of PTX NCs through mimical intestinal epithelial reached 25% in 6 h, demonstrating its comparatively high oral bioavailability in the human body. This work demonstrates the great potential of PTX NC treated in oral delivery.

pH-Sensitive Delivery Vehicle Based on Folic Acid-Conjugated Polydopamine-Modified Mesoporous Silica Nanoparticles for Targeted Cancer Therapy

In this study, we introduced a targeting polymer poly(ethylene glycol)-folic acid (PEG-FA) on the surface of polydopamine (PDA)-modified mesoporous silica nanoparticles (MSNs) to develop the novel nanoparticles (NPs) MSNs@PDA-PEG-FA, which were employed as a drug delivery system loaded with doxorubicin (DOX) as a model drug for cervical cancer therapy. The chemical structure and properties of these NPs were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, N₂ adsorption/desorption, dynamic light scattering-autosizer, thermogravimetric analysis, and Fourier transform infrared spectroscopy. The pH-sensitive PDA coating served as a gatekeeper. The in vitro drug release experiments showed pH-dependent and sustained drug release profiles that could enhance the therapeutic anticancer effect and minimize potential damage to normal cells due to the acidic microenvironment of the tumor. These MSNs@PDA-PEG-FA achieved significantly high targeting efficiency, which was demonstrated by the in vitro cellular uptake and cellular targeting assay. Compared with that of free DOX and DOX-loaded NPs without the folic targeting ligand, the FA-targeted NPs exhibited higher antitumor efficacy in vivo, implying that they are a highly promising potential carrier for cancer treatments.

Intestinal permeation enhancers for oral peptide delivery

Intestinal permeation enhancers (PEs) are one of the most widely tested strategies to improve oral delivery of therapeutic peptides. This article assesses the intestinal permeation enhancement action of over 250 PEs that have been tested in intestinal delivery models. In depth analysis of pre-clinical data is presented for PEs as components of proprietary delivery systems that have progressed to clinical trials. Given the importance of co-presentation of sufficiently high concentrations of PE and peptide at the small intestinal epithelium, there is an emphasis on studies where PEs have been formulated with poorly permeable molecules in solid dosage forms and lipoidal dispersions.

Using peptides to increase transport across the intestinal barrier

The oral route is the preferred for the administration of drugs; however, it has some serious limitations. One of the main disadvantages is poor permeability across the intestinal barrier. Various approaches are currently being adopted to overcome this issue. In this review, we describe the alternatives that use peptides to enhance intestinal absorption. First, we define the various sources of peptide enhancers followed by the analysis of the absorption mechanism used. We then comment on the possible toxic effects derived from their use as permeation enhancers, as well as potential formulation strategies. Finally, the advantages and drawbacks of peptides as intestinal enhancers are examined.

Synthesis and characterization of insulin/zirconium phosphate@TiO2 hybrid composites for enhanced oral insulin delivery applications

In this work, a series of composites of insulin (Ins)/zirconium phosphate (ZrP) were synthesized by intercalation method, then, these composites were coated with TiO₂ by sol-gel method to prepare Ins/ZrP@TiO₂ hybrid composites and the drug release of the composites was investigated by using UV-Vis spectroscopy. Ins/ZrP (10, 30, 60 wt%) composites were prepared by intercalation of insulin into the ZrP layers in water. Then Ins/ZrP composites were coated with different amounts of TiO₂ (30, 50, 100 wt %) by using titanium tetra n-butoxide, as precursor. Formation of intercalated Ins/ZrP and Ins/ZrP@TiO₂ hybrid composites was characterized by FT-IR, FE-SEM, BET and XRD analysis. Zeta potential of the optimized Ins/ZrP@TiO₂ hybrid composite was determined -27.2 mV. Cytotoxic effects of the optimized Ins/ZrP@TiO₂ hybrid composite against HeLa and Hek293T cell lines were evaluated using MTT assay and the results showed that designed drug delivery system was not toxic in biological environment. Compared to the Ins/ZrP composites, incorporation of TiO₂ coating enhanced the drug entrapment considerably, and reduced the drug release. The Ins/ZrP composites without TiO₂ coating released the whole drug after 30 min in pH 7.4 (phosphate buffer solution) while the TiO₂-coated composites released the entrapped drug after 20 h. In addition to increasing the shelf life of hormone, this nanoencapsulation and nanocoating method can convert the insulin utilization from injection to oral and present a painless and more comfortable treatment for diabetics.

Enzyme coated beta-cyclodextrin for effective adsorption and glucose-responsive closed-loop insulin delivery

Inconsistent dosage of insulin (INS) for type 2 diabetes patients lead to severe adverse effects like limb amputation, blindness and fatal hypo or hyper glycaemia. Hence, a drug delivery system (DDS) capable of consistent INS release by sensing changes in blood glucose level is essential. Herein, we report a glucose responsive DDS comprised of oleic acid-grafted-aminated beta cyclodextrin (OA-g-ACD) copolymer, coated with a dispersion of glucose oxidase (GOx) and catalase (CAT). The prepared DDS was characterised using FTIR, Optical Microscopy, H(1) NMR, DLS and SEM. Hydrophobicity and drug loading capacity was ascertained using contact angle measurements and confocal laser scanning microscopy (CLSM) respectively. Extent of swelling was observed to be a function of glucose concentration. INS release profile showed a cumulative release of 78.0 % after 240min. Flow cytometry studies revealed greater population of INS on HeLa cells indicating application of DDS as potential candidate for the intravenous administration of INS.

Nanoparticles for oral delivery: Design, evaluation and state-of-the-art

The oral route is a preferred method of drug administration, though achieving effective drug delivery and minimizing off-target side effects is often challenging. Formulation into nanoparticles can improve drug stability in the harsh gastrointestinal (GI) tract environment, providing opportunities for targeting specific sites in the GI tract, increasing drug solubility and bioavailability, and providing sustained release in the GI tract. However, the unique and diverse physiology throughout the GI tract, including wide variation in pH, mucus that varies in thickness and structure, numerous cell types, and various physiological functions are both a barrier to effective delivery and an opportunity for nanoparticle design. Here, nanoparticle design aspects to improve delivery to particular sites in the GI tract are discussed. We then review new methods for evaluating oral nanoparticle formulations, including a short commentary on data interpretation and translation. Finally, the state-of-the-art in preclinical targeted nanoparticle design is reviewed.

Advances in the transepithelial transport of nanoparticles

The intestinal epithelium represents a barrier to the delivery of nanoparticles (NPs). It prevents intact NPs from efficiently crossing the mucosa to access the circulation, thus limiting the successful application of NP-based oral drug delivery. Recent advances in nanotechnology have provided promising solutions to this challenge. This review describes the potential intestinal absorption pathways of NPs, including the transenterocytic pathway, paracellular pathway and M-cell-mediated pathway. NP properties that influence transcytosis are summarized; and the biodistribution of NPs after oral absorption is described and the future prospects of novel NPs are explored.

Cell-penetrating peptides as tools to enhance non-injectable delivery of biopharmaceuticals

Non-injectable delivery of peptide and protein drugs is hampered by their labile nature, hydrophilicity, and large molecular size; thus limiting their permeation across mucosae, which represent major biochemical and physical barriers to drugs administered via e.g. the oral, nasal, and pulmonary routes. However, in recent years cell-penetrating peptides (CPP) have emerged as promising tools to enhance mucosal delivery of co-administered or conjugated peptide and protein cargo and more advanced CPP-cargo formulations are emerging. CPPs act as transepithelial delivery vectors, but the mechanism(s) by which CPPs mediate cargo translocation across an epithelium is so far poorly understood; both due to the fact that multiple factors influence the resulting uptake and trafficking mechanisms as well as to the complicated nature of sensitive studies of this. In addition to a proper mechanistic understanding, documentation of CPP-mediated delivery in higher animal species than rodent as well as extensive toxicological studies are necessary for CPP-containing non-injectable DDSs to reach the clinic.

Core–shell stability of nanoparticles plays an important role for overcoming the intestinal mucus and epithelium barrier

The stability of the core–shell structure plays an important role in the nanoparticles ability to overcome both the mucus and epithelium absorption barrier.