Region-Dependent Role of Cell-Penetrating Peptides in Insulin Absorption Across the Rat Small Intestinal Membrane

Targeted cancer treatment using folate-conjugated sponge-like ZIF-8 nanoparticles: a review

ZIF-8 (zeolitic imidazolate framework-8) is a potential drug delivery system because of its unique properties, which include a large surface area, a large pore capacity, a large loading capacity, and outstanding stability under physiological conditions. ZIF-8 nanoparticles may be readily functionalized with targeting ligands for the identification and absorption of particular cancer cells, enhancing the efficacy of chemotherapeutic medicines and reducing adverse effects. ZIF-8 is also pH-responsive, allowing medication release in the acidic milieu of cancer cells. Because of its tunable structure, it can be easily functionalized to design cancer-specific targeted medicines. The delivery of ZIF-8 to cancer cells can be facilitated by folic acid-conjugation. Hence, it can bind to overexpressed folate receptors on the surface of cancer cells, which holds the promise of reducing unwanted deliveries. As a result of its importance in cancer treatment, the folate-conjugated ZIF-8 was the major focus of this review.

Advances in buccal and oral delivery of insulin

Diabetes mellitus is a metabolic endocrine disease characterized by chronic hyperglycemia with disturbances in metabolic processes, such as those related to carbohydrates, fat, and protein. There are two main types of this disease: type 1 diabetes (T1D) and type 2 diabetes (T2D). Insulin therapy is pivotal to the management of diabetes. Over the last two decades, many routes of administration, including nasal, pulmonary, rectal, transdermal, buccal, and ocular, have been investigated. Nevertheless, subcutaneous parenteral administration is still the most common route for insulin therapy. To overcome poor bioavailability and the barriers to oral insulin absorption, novel approaches in the field of oral drug delivery and administration have been brought about by the coalescence of different branches of nanoscience and nanotechnology, such as nanomedicine, nano-biochemistry, and nano-pharmacy. Novel drug delivery systems, including nanoparticles, nano-platforms, and nanocarriers, have been suggested. The objective of this review is to provide an update on the various promising approaches that have been explored and evaluated for the safe and efficient oral and buccal administration of insulin.

Stereochemistry and Intermolecular Interactions Influence Carrier Peptide-Mediated Insulin Delivery

The inherent low oral bioavailability of therapeutic peptides can be enhanced by the cell-penetrating peptide penetratin and its analogues shuffle and penetramax applied as carriers for delivery of insulin. In this study, the objective was to gain mechanistic insights on the effect of the carrier peptide stereochemistry on their interactions with insulin and on insulin delivery. Insulin-carrier peptide interactions were investigated using small-angle X-ray scattering and cryogenic transmission electron microscopy, while the insulin and peptide stability and transepithelial insulin permeation were evaluated in the Caco-2 cell culture model along with the carrier peptide-induced effects on epithelial integrity and cellular metabolic activity. Interestingly, the insulin transepithelial permeation was influenced by the degree of insulin-carrier peptide complexation and depended on the stereochemistry of penetramax but not of penetratin and shuffle. The l-form of the peptides initially decreased the epithelial integrity comparable to that induced by the d-peptides, suggesting a comparable mechanism of action. The immediate decrease was reversible during exposure of the Caco-2 epithelium to the l-peptides but not during exposure to the d-peptides, likely a result of their higher stability. Overall, exploration of the stereochemistry showed to be an interesting strategy for carrier peptide-mediated insulin delivery.

Insulin-loaded liposomes packaged in alginate hydrogels promote the oral bioavailability of insulin

Compared to subcutaneous injections, oral administration of insulin would be a preferred route of drug administration for diabetic patients. For oral delivery, both liposomes and alginate hydrogels face many challenges, including early burst release of the encapsulated drug and poor intestinal drug absorption. Also, adhesion to the intestinal mucosa remains weak, which all result in a low bioavailability of the payload. This study reports on an alginate hydrogel loaded with liposomes for oral insulin administration. Liposomes (Lip) loaded with arginine-insulin complexes (AINS) were incorporated into a hydrogel prepared from cysteine modified alginate (Cys-Alg) to form liposome-in-alginate hydrogels (AINS-Lip-Gel). An ex vivo study proves that intestinal permeation of AINS and AINS-Lip is approximately 2.0 and 6.0-fold, respectively, higher than that of free insulin. The hydrogel retarded early release of insulin (∼30%) from the liposomes and enhanced the intestinal mucosal retention. In vivo experiments revealed that the AINS-Lip-Gel released insulin in a controlled manner and possessed strong hypoglycemic effects. We conclude that liposome-in-alginate hydrogels loaded with AINS represent an attractive strategy for the oral delivery of insulin.

Cell-Penetrating Peptides as Carriers for Transepithelial Drug Delivery

This chapter describes the use of cell-penetrating peptides (CPPs) as carriers for transepithelial delivery of therapeutic peptides. Assessment of transepithelial peptide permeation and the mechanisms of action that permeability enhancing drug carriers exert on the epithelium requires subtle sample preparation and analysis by orthogonal methods. Here, the preparation and use of CPP-insulin physical mixture samples including the quantification of insulin by enzyme-linked immunosorbent assay (ELISA) is described. In addition, effects of CPPs on the epithelium and its barrier properties immediately upon exposure and after a recovery period are evaluated by epithelial cell viability, transepithelial electrical resistance, immunostaining of the tight junction associated zonula occludens (ZO-1) protein, and actin cytoskeleton staining.

Intestinal permeation enhancers to improve oral bioavailability of macromolecules: reasons for low efficacy in humans

INTRODUCTION

Intestinal permeation enhancers (PEs) are substances that transiently alter the intestinal epithelial barrier to facilitate permeation of macromolecules with low oral bioavailability (BA). While a number of PEs have progressed to clinical testing in conventional formulations with macromolecules, there has been only low single digit increases in oral BA, irrespective of whether the drug met primary or secondary clinical endpoints.

AREAS COVERED

This article considers the causes of sub-optimal BA of macromolecules from PE dosage forms and suggests approaches that may improve performance in humans.

EXPERT OPINION

Permeation enhancement is most effective when the PE is co-localized with the macromolecule at the epithelial surface. Conditions in the GI tract impede optimal co-localization. Novel delivery systems that limit dilution and spreading of the PE and macromolecule in the small intestine have attempted to replicate promising enhancement efficacy observed in static drug delivery models.

Impact Of Penetratin Stereochemistry On The Oral Bioavailability Of Insulin-Loaded Solid Lipid Nanoparticles

Purpose

This study evaluated the stereoisomeric effect of L- and D-penetratin—cell-penetrating peptides (CPPs)—incorporated insulin-loaded solid lipid nanoparticles (INS-SLNs) on the bioavailability (BA) of oral insulin (INS).

Methods

Insulin-loaded solid nanoparticles, L-penetratin-INS-SLNs (LP-INS-SLNs), and D-penetratin-INS-SLNs (DP-INS-SLNs) were formulated by double emulsification. The developed SLNs were evaluated for particle size, zeta potential (ZP), and drug encapsulation and subjected to differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and evaluated for stability against enzymatic degradation in rat intestinal fluid. Finally, the SLNs were administered to rats to evaluate the BA of INS-SLNs that contained L- and D-penetratin.

Results

The mean particle size, PDI, and ZP values of INS-SLNs, LP-INS-SLNs, and DP-INS-SLNs ranged from 618.5 to 973.0 nm, 0.227 to 0.734, and −17.0 to −23.7 mV, respectively. The encapsulation efficiency (%EE) and drug loading (%DL) of INS-SLNs, LP-INS-SLNs, and DP-INS-SLNs ranged from 59.03% to 67.42% and from 1.62% to 1.82%, respectively. Differential scanning calorimetry and FTIR analyses indicated that INS was successfully encapsulated in SLNs. Enzymatic degradation of DP-INS-SLNs was slower in intestinal fluid, and the half-life (t_1/2) was significantly prolonged, compared to all other SLNs. The pharmacological availability (PA) and BA of orally administered LP-INS-SLNs, which were the most effective SLNs, were 13.1% and 15.7% relative to s.c. administration, respectively.

Conclusion

Penetratin stereochemistry significantly impacted oral BA of INS-SLNs, which are promising carriers for oral INS administration.

Hydrophobic Amino Acid Tryptophan Shows Promise as a Potential Absorption Enhancer for Oral Delivery of Biopharmaceuticals

Cell-penetrating peptides (CPPs) have great potential to efficiently deliver drug cargos across cell membranes without cytotoxicity. Cationic arginine and hydrophobic tryptophan have been reported to be key component amino acids for cellular internalization of CPPs. We recently found that l-arginine could increase the oral delivery of insulin in its single amino acid form. Therefore, in the present study, we evaluated the ability of another key amino acid, tryptophan, to enhance the intestinal absorption of biopharmaceuticals. We demonstrated that co-administration with l-tryptophan significantly facilitated the oral and intestinal absorption of the peptide drug insulin administered to rats. Furthermore, l-tryptophan exhibited the ability to greatly enhance the intestinal absorption of other peptide drugs such as glucagon-like peptide-1 (GLP-1), its analog Exendin-4 and macromolecular hydrophilic dextrans with molecular weights ranging from 4000 to 70,000 g/mol. However, no intermolecular interaction between insulin and l-tryptophan was observed and no toxic alterations to epithelial cellular integrity-such as changes to cell membranes, cell viability, or paracellular tight junctions-were found. This suggests that yet to be discovered inherent biological mechanisms are involved in the stimulation of insulin absorption by co-administration with l-tryptophan. These results are the first to demonstrate the significant potential of using the single amino acid l-tryptophan as an effective and versatile bioavailability enhancer for the oral delivery of biopharmaceuticals.

Advance in oral delivery systems for therapeutic protein

Oral delivery is the most common method of drug administration with high safety and good compliance for patients. However, delivering therapeutic proteins to the target site via oral route involves tremendous challenge due to unfavourable conditions like biochemical barrier, mucus barrier and epithelial barriers. According to the functional differences of various protein drug delivery systems, the recent advances in pH responsive polymer-based drug delivery system, mucoadhesive polymer-based drug delivery system, absorption enhancers-based drug delivery system and composite polymer-based delivery system all were briefly summarised in this review, which not only clarified the clinic potential of these novel drug delivery systems, but also described the way for increasing oral bioavailability of therapeutic protein.

Stereochemistry as a determining factor for the effect of a cell-penetrating peptide on cellular viability and epithelial integrity

Cell-penetrating peptides (CPPs) comprise efficient peptide-based delivery vectors. Owing to the inherent poor enzymatic stability of peptides, CPPs displaying partial or full replacement of l-amino acids with the corresponding d-amino acids might possess advantages as delivery vectors. Thus, the present study aims to elucidate the membrane- and metabolism-associated effects of l-Penetratin (l-PEN) and its corresponding all-d analog (d-PEN). These effects were investigated when exerted on hepatocellular (HepG2) or intestinal (Caco-2 and IEC-6) cell culture models. The head-to-head comparison of these enantiomeric CPPs included evaluation of their effects on cell viability and morphology, epithelial membrane integrity, and cellular ultrastructure. In all investigated cell models, a rapid decrease in cell viability, pronounced membrane perturbation and an altered ultrastructure were detected upon exposure to d-PEN. At equimolar concentrations, these observations were less pronounced or even absent for cells exposed to l-PEN. Both CPPs remained stable for at least 2 h during exposure to proliferating cells (cultured for 24 h), although d-PEN exhibited a longer half-life when compared with that of l-PEN when exposed to well-differentiated cell monolayers (cultured for 18-20 days). Thus, the stereochemistry of the CPP penetratin significantly influences its effects on cell viability and epithelial integrity when profiled against a panel of mammalian cells.

Scalable production of core-shell nanoparticles by flash nanocomplexation to enhance mucosal transport for oral delivery of insulin

Scalable manufacturing continues to present a major barrier for clinical translation of nanotherapeutics. Methods available for fabricating protein-encapsulating nanoparticles in a scalable fashion are scarce. Protein delivery often requires multiple functionalities to be incorporated into the same vehicle. Specifically for nanoparticle-mediated oral delivery of protein therapeutics, protection in GI tract, site-specific release, facilitating transmucosal permeation, and enhancing epithelial transport are a few desirable features to be engineered into a nanoparticle system. Here we devised a sequential flash nanocomplexation (FNC) technique for the scalable production of a core-shell structured nanoparticle system by combining materials choice and particle size and structure to fulfill these functions, therefore enhancing the delivery efficiency of insulin. This method is highly effective in controlling the size, generating core-shell structure with high encapsulation efficiency (97%) and payload capacity (67%) using insulin/l-penetratin complex nanoparticles as a core coated with hyaluronic acid (HA). Both the in vitro and in vivo models confirmed that the HA coating on these core-shell nanoparticles enhanced the permeation of nanoparticles through the intestinal mucus layer and improved trans-epithelial absorption of insulin nanoparticles; and the enhancement effect was most prominent using HA with the highest average molecular weight. The insulin-loaded nanoparticles were then encapsulated into enteric microcapsules (MCs) in an FNC process to provide additional protection against the acidic environment in the stomach while allowing rapid release of insulin nanoparticles when they reach small intestine. The optimized multifunctional MCs delivered an effective glucose reduction in a Type I diabetes rat model following a single oral administration, yielding a relative bioavailability of 11% in comparison with subcutaneous injection of free-form insulin. This FNC technique is highly effective in controlling particle size and structure to improve delivery properties and function. It can be easily extended to oral delivery for other protein therapeutics.

Potential of single cationic amino acid molecule "Arginine" for stimulating oral absorption of insulin

We have reported that cell-penetrating peptides, such as oligoarginine, act as powerful absorption enhancers for the development of oral insulin delivery systems. However, the minimal essential sequence of oligoarginine that stimulates intestinal insulin absorption remains unclear. Therefore, the present study was conducted to clarify this minimum sequence of oligoarginine and to examine the effect of single cationic amino acid arginine on the intestinal and oral absorption of insulin. The results demonstrated that a remarkable enhancement of intestinal insulin absorption was observed after coadministration of insulin with l-arginine. The efficacy of d-forms of oligoarginine/arginine tended to decrease with a decreasing number of amino acid residues, whereas the effect of l-arginine was the strongest of any of the l-forms of oligoarginine/arginine. Interestingly, the effect of l-arginine was stronger than that of d-arginine at various concentrations, and the effect of other cationic amino acids such as lysine and histidine was relatively lower than that of arginine. In addition, no leakage of lactate dehydrogenase from the intestinal epithelium and no change in the transepithelial electrical resistance of a Caco-2 cell monolayer were detected after administration of l-arginine as the single amino acid, which suggests that there were no undesirable effects of arginine on the integrity of cell membranes and paracellular tight junctions. Oral administration study in mice demonstrated that the stronger hypoglycemic effects were observed after coadministration of insulin with l-arginine. In this study, we found that arginine is a key cationic amino acid for delivering insulin across intestinal epithelial barriers and hopefully accelerating the clinical development of oral insulin delivery systems.

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.

Use of a non-covalent cell-penetrating peptide strategy to enhance the nasal delivery of interferon beta and its PEGylated form

The conjugation of therapeutic proteins to polyethylene glycol (PEG) is known as PEGylation. It improves their retention in the body and reduces the frequency of injections. Development of noninvasive delivery systems for biopharmaceuticals can improve the patients' quality of life. The present study aimed to evaluate the cell-penetrating peptides (CPPs), which act as bioenhancers, for the nasal delivery of protein drug interferon beta (IFN-β) and its PEGylated form (PEG-IFN-β). The ability of CPPs to enhance the nasal mucosal absorption of unmodified IFN-β was assessed in rats. It was shown that only d-amino acid forms of amphipathic CPPs, penetratin and PenetraMax significantly enhanced the nasal absorption of IFN-β. Especially, D-penetratin (up to 2mM) enhanced the absorption of INF-β in a dose-dependent manner. The maximum absolute bioavailability reached 8.26% following in situ nasal coadministration of IFN-β with d-penetratin (2mM). Furthermore, it was found that the coadministration of d-penetratin also facilitated the nasal absorption of PEG-IFN-β, which remained in the circulation for more than 6h. Moreover, the toxicity assessments showed no damage to the epithelial membranes after nasal administration of CPPs including penetratin and PenetraMax. Altogether, this study provides the first evidence that the noncovalent coadministration of PEGylated proteins with CPPs could be a potent strategy for the noninvasive and sustained nasal delivery of therapeutic proteins.

α-synuclein conformational antibodies fused to penetratin are effective in models of Lewy body disease

Objective

Progressive accumulation of α‐synuclein (α‐syn) has been associated with Parkinson's disease (PD) and Dementia with Lewy body (DLB). The mechanisms through which α‐syn leads to neurodegeneration are not completely clear; however, the formation of various oligomeric species have been proposed to play a role. Antibody therapy has shown effectiveness at reducing α‐syn accumulation in the central nervous system (CNS); however, most of these studies have been conducted utilizing antibodies that recognize both monomeric and higher molecular weight α‐syn. In this context, the main objective of this study was to investigate the efficacy of immunotherapy with single‐chain antibodies (scFVs) against specific conformational forms of α‐syn fused to a novel brain penetrating sequence.

Method

We screened various scFVs against α‐syn expressed from lentiviral vectors by intracerebral injections in an α‐syn tg model. The most effective scFVs were fused to the cell‐penetrating peptide penetratin to enhance transport across the blood–brain barrier, and lentiviral vectors were constructed and tested for efficacy following systemic delivery intraperitoneal into α‐syn tg mice.

Result

Two scFVs (D5 and 10H) selectively targeted different α‐syn oligomers and reduced the accumulation of α‐syn and ameliorated functional deficits when delivered late in disease development; however, only one of the antibodies (D5) was also effective when delivered early in disease development. These scFVs were also utilized in an enzyme‐linked immunosorbent assay (ELISA) assay to monitor the effects of immunotherapy on α‐syn oligomers in brain and plasma.

Interpretation

The design and targeting of antibodies for specific species of α‐syn oligomers is crucial for therapeutic immunotherapy and might be of relevance for the treatment of Lewy body disease.