Oral Colon-Specific Drug Delivery of Protein and Peptide Drugs

Barriers and Strategies for Oral Peptide and Protein Therapeutics Delivery: Update on Clinical Advances

Peptide and protein (PP) therapeutics are highly specific and potent biomolecules that treat chronic and complex diseases. However, their oral delivery is significantly hindered by enzymatic degradation, instability, and poor permeability through the gastrointestinal (GI) epithelium, resulting in low bioavailability. Various strategies have emerged as transformative solutions to address existing challenges, offering enhanced protection, stabilization, and absorption of PPs. These strategies primarily focus on two major challenges: protecting the PP against harsh conditions and enhancing permeation across the intestinal membrane. Innovative approaches such as pH modulation and incorporation of enzyme inhibitors are usually used to mitigate proteolytic degradation of PP during transit across the GI tract. In a similar vein, absorption enhancers and prodrug strategies facilitate epithelial transport, while targeted delivery systems focus on specific areas of the GI tract to enhance absorption. Likewise, mucus-penetrating and mucoadhesive strategies have enhanced retention and interaction with epithelial cells, effectively overcoming barriers like the mucus layer and tight epithelial junctions. Furthermore, structural modifications such as lipidation, peptide cyclization, and polyethylene glycosylation are promising alternatives to render stability, prolong circulation time, and membrane permeability. In particular, functional biomaterials, active targeting, and lymphatic transport strategies have provided new platforms for oral PP delivery. Advancing in materials science, nanotechnology, and the disruption of medical devices holds new frontiers to overcome barriers. Despite substantial advancements, the limited success in clinical translation underscores the urgency of innovative strategies. This review presents oral PPs as a promising platform, highlighting the key barriers and strategies to transform their therapeutic landscapes.

The Current and Promising Oral Delivery Methods for Protein- and Peptide-Based Drugs

Drugs based on peptides and proteins (PPs) have been widely used in medicine, beginning with insulin therapy in patients with diabetes mellitus over a century ago. Although the oral route of drug administration is the preferred one by the vast majority of patients and improves compliance, medications of this kind due to their specific chemical structure are typically delivered parenterally, which ensures optimal bioavailability. In order to overcome issues connected with oral absorption of PPs such as their instability depending on digestive enzymes and pH changes in the gastrointestinal (GI) system on the one hand, but also their limited permeability across physiological barriers (mucus and epithelium) on the other hand, scientists have been strenuously searching for novel delivery methods enabling peptide and protein drugs (PPDs) to be administered enterally. These include utilization of different nanoparticles, transport channels, substances enhancing permeation, chemical modifications, hydrogels, microneedles, microemulsion, proteolytic enzyme inhibitors, and cell-penetrating peptides, all of which are extensively discussed in this review. Furthermore, this article highlights oral PP therapeutics both previously used in therapy and currently available on the medical market.

Oral Insulin Delivery: A Review on Recent Advancements and Novel Strategies

BACKGROUND

Due to the lifestyle of people in the community in recent years, the prevalence of diabetes mellitus has increased, so New drugs and related treatments are also being developed.

INTRODUCTION

One of the essential treatments for diabetes today is injectable insulin forms, which have their problems and limitations, such as invasive and less admission of patients and high cost of production. According to the mentioned issues, Theoretically, Oral insulin forms can solve many problems of injectable forms.

METHODS

Many efforts have been made to design and introduce Oral delivery systems of insulin, such as lipid-based, synthetic polymer-based, and polysaccharide-based nano/microparticle formulations. The present study reviewed these novel formulations and strategies in the past five years and checked their properties and results.

RESULTS

According to peer-reviewed research, insulin-transporting particles may preserve insulin in the acidic and enzymatic medium and decrease peptide degradation; in fact, they could deliver appropriate insulin levels to the intestinal environment and then to blood. Some of the studied systems increase the permeability of insulin to the absorption membrane in cellular models. In most investigations, in vivo results revealed a lower ability of formulations to reduce BGL than subcutaneous form, despite promising results in in vitro and stability testing.

CONCLUSION

Although taking insulin orally currently seems unfeasible, future systems may be able to overcome mentioned obstacles, making oral insulin delivery feasible and producing acceptable bioavailability and treatment effects in comparison to injection forms.

Solidification and oral delivery of biologics to the colon- A review

The oral delivery of biologics such as therapeutic proteins, peptides and oligonucleotides for the treatment of colon related diseases has been the focus of increasing attention over the last years. However, the major disadvantage of these macromolecules is their degradation propensity in liquid state which can lead to the undesirable and complete loss of function. Therefore, to increase the stability of the biologic and reduce their degradation propensity, formulation techniques such as solidification can be performed to obtain a stable solid dosage form for oral administration. Due to their fragility, stress exerted on the biologic during solidification has to be reduced with the incorporation of stabilizing excipients into the formulation. This review focuses on the state-of-the-art solidification techniques required to obtain a solid dosage form for the oral delivery of biologics to the colon and the use of suitable excipients for adequate stabilization upon solidification. The solidifying processes discussed within this review are spray drying, freeze drying, bead coating and also other techniques such as spray freeze drying, electro spraying, vacuum- and supercritical fluid drying. Further, the colon as site of absorption in both healthy and diseased state is critically reviewed and possible oral delivery systems for biologics are discussed.

Immunogenicity of Different Types of Adjuvants and Nano-Adjuvants in Veterinary Vaccines: A Comprehensive Review

Vaccination is the best way to prevent and reduce the damage caused by infectious diseases in animals and humans. So, several vaccines are used for prophylactic purposes before the pathogen infects, while therapeutic vaccines strengthen the immune system after infection with the pathogen. Adjuvants are molecules, compounds, or macromolecules that enhance non-specific immunity and, in collaboration with antigen(s), can improve the body's immune responses and change the type of immune response. The potential and toxicity of adjuvants must be balanced to provide the safest stimulation with the fewest side effects. In order to overcome the limitations of adjuvants and the effective and controlled delivery of antigens, attention has been drawn to nano-carriers that can be a promising platform for better presenting and stimulating the immune system. Some studies show that nanoparticles have a more remarkable ability to act as adjuvants than microparticles. Because nano-adjuvants inactively target antigen-presenting cells (APCs) and change their chemical surface, nanoparticles also perform better in targeted antigen delivery because they cross biological barriers more easily. We collected and reviewed various types of nano-adjuvants with their specific roles in immunogenicity as a prominent strategy used in veterinary vaccines in this paper.

Design, Development, and Optimisation of Smart Linker Chemistry for Targeted Colonic Delivery-In Vitro Evaluation

Drug targeting is necessary to deliver drugs to a specific site of action at a rate dictated by therapeutic requirements. The pharmacological action of a drug can thereby be optimised while minimising adverse effects. Numerous colonic drug delivery systems have been developed to avoid such undesirable side effects; however, these systems lack site specificity, leaving room for further improvement. The objective of the present study was to explore the potential of amino-alkoxycarbonyloxymethyl (amino-AOCOM) ether prodrugs as a general approach for future colonic delivery. To circumvent inter- and intra-subject variabilities in enzyme activities, these prodrugs do not rely on enzymes but rather are activated via a pH-triggered intramolecular cyclisation−elimination reaction. As proof of concept, model compounds were synthesised and evaluated under various pH conditions, simulating various regions of the gastrointestinal tract (GIT). Probe 15 demonstrated excellent stability under simulated stomach- and duodenum-like conditions and protected 60% of the payload in a small intestine-like environment. Moreover, 15 displayed sustained release at colonic pH, delivering >90% of the payload over 38 h. Mesalamine (Msl) prodrugs 21 and 22 were also synthesised and showed better stability than probe 15 in the simulated upper GIT but relatively slower release at colonic pH (61−68% of Msl over 48 h). For both prodrugs, the extent of release was comparable to that of the commercial product Asacol. This study provides initial proof of concept regarding the use of a cyclisation-activated prodrug for colon delivery and suggests that release characteristics still vary on a case-by-case basis.

Polymer Encapsulated Liposomes for Oral Co-Delivery of Curcumin and Hydroxytyrosol

Curcumin (Cur) is a hydrophobic polyphenol from the rhizome of Curcuma spp., while hydroxytyrosol (HT) is a water-soluble polyphenol from Olea europaea. Both show outstanding antioxidant properties but suffer from scarce bioavailability and low stability in biological fluids. In this work, the co-encapsulation of Cur and HT into liposomes was realized, and the liposomal formulation was improved using polymers to increase their survival in the gastrointestinal tract. Liposomes with different compositions were formulated: Type 1, composed of phospholipids and cholesterol; Type 2, also with a PEG coating; and Type 3 providing an additional shell of Eudragit^® S100, a gastro-resistant polymer. Samples were characterized in terms of size, morphology, ζ-potential, encapsulation efficiency, and loading capacity. All samples were subjected to a simulated in vitro digestion and their stability was investigated. The Eudragit^®S100 coating demonstrated prevention of early releases of HT in the mouth and gastric phases, while the PEG shell reduced bile salts and pancreatin effects during the intestinal digestion. In vitro antioxidant activity showed a cumulative effect for Cur and HT loaded in vesicles. Finally, liposomes with HT concentrations up to 40 μM and Cur up to 4.7 μM, alone or in combination, did not show cytotoxicity against Caco-2 cells.

Preparation, Characterization and In Vitro Evaluation of Eudragit S100-Coated Bile Salt-Containing Liposomes for Oral Colonic Delivery of Budesonide

The aim of this study was to prepare a liposomal formulation of a model drug (budesonide) for colonic delivery by incorporating a bile salt (sodium glycocholate, SGC) into liposomes followed by coating with a pH-responsive polymer (Eudragit S100, ES100). The role of the SGC is to protect the liposome from the emulsifying effect of physiological bile salts, while that of ES100 is to protect the liposomes from regions of high acidity and enzymatic activity in the stomach and small intestine. Vesicles containing SGC were prepared by two preparation methods (sonication and extrusion), and then coated by ES100 (ES100-SGC-Lip). ES100-SGC-Lip showed a high entrapment efficiency (>90%) and a narrow size distribution (particle size = 275 nm, polydispersity index < 0.130). The characteristics of liposomes were highly influenced by the concentration of incorporated SGC. The lipid/polymer weight ratio, liposome charge, liposome addition, and mixing rate were critical factors for efficient and uniform coating. In vitro drug release studies in various simulated fluids indicate a pH-dependent dissolution of the coating layer, and the disintegration process of ES100-SGC-Lip was evaluated. In conclusion, the bile salt-containing ES100-coated liposomal formulation has potential for effective oral colonic drug delivery.

Administration strategies and smart devices for drug release in specific sites of the upper GI tract

Targeting the release of drugs in specific sites of the upper GI tract would meet local therapeutic goals, improve the bioavailability of specific drugs and help overcoming compliance-related limitations, especially in chronic illnesses of great social/economic impact and involving polytherapies (e.g. Parkinson's and Alzeimer's disease, tubercolosis, malaria, HIV, HCV). It has been traditionally pursued using gastroretentive (GR) systems, i.e. low-density, high-density, magnetic, adhesive and expandable devices. More recently, the interest towards oral administration of biologics has prompted the development of novel drug delivery systems (DDSs) provided with needles and able to inject different formulations in the mucosa of the upper GI tract and particularly of esophagus, stomach or small intestine. Besides comprehensive literature analysis, DDSs identified as smart devices in view of their high degree of complexity in terms of design, working mechanism, materials employed and manufacturing steps were discussed making use of graphic tools.

Efficient oral insulin delivery enabled by transferrin-coated acid-resistant metal-organic framework nanoparticles

Oral protein delivery is considered a cutting-edge technology to improve patients' quality of life, offering superior patient compliance and convenience compared with injections. However, oral protein formulation has stagnated because of the instability and inefficient penetration of protein in the gastrointestinal tract. Here, we used acid-resistant metal-organic framework nanoparticles (UiO-68-NH₂) to encapsulate sufficient insulin and decorated the exterior with targeting proteins (transferrin) to realize highly efficient oral insulin delivery. The UiO-68-NH₂ nanocarrier with proper pore size achieved high insulin loading while protecting insulin from acid and enzymatic degradation. Through receptor-mediated transcellular pathway, the transferrin-coated nanoparticles realized efficient transport across the intestinal epithelium and controlled insulin release under physiological conditions, leading to a notable hypoglycemic effect and a high oral bioavailability of 29.6%. Our work demonstrates that functional metal-organic framework nanoparticles can protect proteins from the gastric environment and overcome the intestinal barrier, thus providing the possibility for oral biomacromolecule delivery.

Clinical translation of advanced colonic drug delivery technologies

Targeted drug delivery to the colon offers a myriad of benefits, including treatment of local diseases, direct access to unique therapeutic targets and the potential for increasing systemic drug bioavailability and efficacy. Although a range of traditional colonic delivery technologies are available, these systems exhibit inconsistent drug release due to physiological variability between and within individuals, which may be further exacerbated by underlying disease states. In recent years, significant translational and commercial advances have been made with the introduction of new technologies that incorporate independent multi-stimuli release mechanisms (pH and/or microbiota-dependent release). Harnessing these advanced technologies offers new possibilities for drug delivery via the colon, including the delivery of biopharmaceuticals, vaccines, nutrients, and microbiome therapeutics for the treatment of both local and systemic diseases. This review details the latest advances in colonic drug delivery, with an emphasis on emerging therapeutic opportunities and clinical technology translation.

Design and evaluation of IKK-activated GSK3β inhibitory peptide as an inflammation-responsive anti-colitic therapeutic

Glycogen synthase kinase-3β (GSK3β), a multi-functional kinase, is a promising therapeutic target for the treatment of inflammation. Inhibitory κB kinase (IKK)-activated GSK3β inhibitory peptide (IAGIP) was designed as an inflammation-responsive anti-colitic therapeutic. To optimize therapeutic efficiency, IAGIP was tested using two different drug delivery techniques: colon-targeted delivery and cell-permeable peptide modification. In cell-based experiments, in response to tumor necrosis factor (TNF)- and lipopolysaccharide (LPS)-mediated activation of IKK, cell-permeable IAGIP (CTP-IAGIP) inhibited GSK3β, leading to increased production of anti-inflammatory cytokine interleukin-10 (IL-10) and suppression of TNF- and LPS-induced NFκB activity. Oral gavage of CTP-IAGIP loaded in the colon-targeted capsule attenuated 2,4,6-trinitrobenzene sulfonic acid-induced rat colitis and lowered the expression levels of NFκB-regulated proteins in the inflamed colons. CTP-IAGIP further induced IL-10 production in the inflamed colonic tissues; however, the levels of IL-10 were not affected in the normal colonic tissue or colonic tissue in which inflammation had subsided. Collectively, our data suggest that IAGIP administered using the aforementioned drug delivery techniques is an orally active anti-colitic drug selectively responding to inflammation.

Oral delivery of proteins and peptides: Challenges, status quo and future perspectives

Proteins and peptides (PPs) have gradually become more attractive therapeutic molecules than small molecular drugs due to their high selectivity and efficacy, but fewer side effects. Owing to the poor stability and limited permeability through gastrointestinal (GI) tract and epithelia, the therapeutic PPs are usually administered by parenteral route. Given the big demand for oral administration in clinical use, a variety of researches focused on developing new technologies to overcome GI barriers of PPs, such as enteric coating, enzyme inhibitors, permeation enhancers, nanoparticles, as well as intestinal microdevices. Some new technologies have been developed under clinical trials and even on the market. This review summarizes the history, the physiological barriers and the overcoming approaches, current clinical and preclinical technologies, and future prospects of oral delivery of PPs.

Formulation development and in-vitro/ex-vivo evaluation for a polysaccharide-based colon targeted matrix tablet

OBJECTIVE

The objective of this study was to develop and optimize a microflora-triggered colon targeted sustained-release dosage form using gum ghatti (GG) and hydroxypropyl methylcellulose (HPMC K100).

METHODS

GG and HPMC K100 were used to prepare microflora triggered colon targeted sustained-release dosage form. For evaluation, two different tablets comprising metoprolol succinate and mesalamine as an active ingredient were used with the objective of developing a platform technology for various categories of drugs. The tablets were coated with Eudragit® L100 and Eudragit® S100 to provide enteric coating and evaluated for hardness, thickness, friability, weight variation, disintegration, and drug content. In vitro release studies for the prepared tablets were carried out mimicking the physiological transit time. Further, the effects of microflora were evaluated using rat cecal content.

RESULTS

The in vitro dissolution profile of coated matrix tablets showed that 86.03±0.43% of metoprolol succinate and 80.26±0.67% of mesalamine were released at the end of 12 h. The ex vivo dissolution profile of coated matrix tablets showed that 96.50±0.27% of metoprolol succinate and 92.58±0.39% of mesalamine were released at the end of 12 h in the presence of rat ceacal content. The developed formulation was stable when subjected to the standard ICH stability study conditions.

CONCLUSION

The result of this study showed that gum ghatti together with hydroxypropyl methylcellulose could be successfully used for the preparation of microflora triggered colon targeted matrix tablets.

An orally available PD-1/PD-L1 blocking peptide OPBP-1-loaded trimethyl chitosan hydrogel for cancer immunotherapy

Blockade of the immune checkpoint PD-1/PD-L1 with monoclonal antibodies demonstrated unprecedented clinical efficacies in many cancers. But the orally available low molecular weight inhibitors remain infancy. Compared to small molecules, peptide exhibits better selectivity and fewer side effects, but poor half-life and a big challenge to be orally administrated. Here, we developed a proteolysis-resistant D peptide OPBP-1 (Oral PD-L1 Binding Peptide 1) which could selectively bind PD-L1, significantly block PD-1/PD-L1 interaction and enhance IFN-γ (interferon γ) secretion from CD8⁺ T cells in human PBMCs (Peripheral blood mononuclear cells). OPBP-1 could significantly inhibit tumor growth in murine colorectal CT26 and melanoma B16-OVA models at a relatively low dose of 0.5 mg/kg, with enhancing the infiltration and function of CD8⁺ T cells. More interestingly, oral delivery of OPBP-1 loaded TMC (N, N, N-trimethyl chitosan) hydrogel (OPBP-1@TMC) showed promising OPBP-1 oral bioavailability (52.8%) and prolonged half-life (14.55 h) in rats, and also significantly inhibited tumor growth in CT26 model. In conclusion, we discovered and optimized a PD-1/PD-L1 blocking peptide OPBP-1, and subsequently loaded into a TMC based hydrogel oral delivery system, in order to maximally elevate the oral bioavailability of the peptide drug and effectively inhibit tumor growth. These results opened up a new prospect for oral drug development in cancer immunotherapy.

Enhanced oral delivery of insulin via the colon-targeted nanocomposite system of organoclay/glycol chitosan/Eudragit®S100

This study aimed to develop a ternary nanocomposite system of organoclay, glycol-chitosan, and Eudragit^®S100 as an effective colon targeted drug delivery carrier to enhance the oral absorption of insulin. A nanocomplex of insulin and aminoclay was prepared via spontaneous co-assembly, which was then coated with glycol-chitosan and Eudragit S^®100 (EGAC-Ins). The double coated nanocomplex, EGAC-Ins demonstrated a high entrapment efficiency of greater than 90% and a pH-dependent drug release. The conformational stability of insulin entrapped in EGAC-Ins was effectively maintained in the presence of proteolytic enzymes. When compared to a free insulin solution, EGAC-Ins enhanced drug permeability by approximately sevenfold in Caco-2 cells and enhanced colonic drug absorption in rats. Accordingly, oral EGAC-Ins significantly reduced blood glucose levels in diabetic rats while the hypoglycemic effect of an oral insulin solution was negligible. In conclusion, EGAC-Ins should be a promising colonic delivery system for improving the oral absorption of insulin.

Zwitterionic micelles efficiently deliver oral insulin without opening tight junctions

Oral delivery of protein drugs is considered a life-changing solution for patients who require regular needle injections. However, clinical translation of oral protein formulations has been hampered by inefficient penetration of drugs through the intestinal mucus and epithelial cell layer, leading to low absorption and bioavailability, and safety concerns owing to tight junction openings. Here we report a zwitterionic micelle platform featuring a virus-mimetic zwitterionic surface, a betaine side chain and an ultralow critical micelle concentration, enabling drug penetration through the mucus and efficient transporter-mediated epithelial absorption without the need for tight junction opening. This micelle platform was used to fabricate a prototype oral insulin formulation by encapsulating a freeze-dried powder of zwitterionic micelle insulin into an enteric-coated capsule. The biocompatible oral insulin formulation shows a high oral bioavailability of >40%, offers the possibility to fine tune insulin acting profiles and provides long-term safety, enabling the oral delivery of protein drugs.

Heme-Derived Metabolic Signals Dictate Immune Responses

Heme is one of the most abundant molecules in the body acting as the functional core of hemoglobin/myoglobin involved in the O2/CO2 carrying in the blood and tissues, redox enzymes and cytochromes in mitochondria. However, free heme is toxic and therefore its removal is a significant priority for the host. Heme is a well-established danger-associated molecular pattern (DAMP), which binds to toll-like receptor 4 (TLR4) to induce immune responses. Heme-derived metabolites including the bile pigments, biliverdin (BV) and bilirubin (BR), were first identified as toxic drivers of neonatal jaundice in 1800 but have only recently been appreciated as endogenous drivers of multiple signaling pathways involved in protection from oxidative stress and regulators of immune responses. The tissue concentration of heme, BV and BR is tightly controlled. Heme oxygenase-1 (HO-1, encoded by HMOX1) produces BV by heme degradation, while biliverdin reductase-A (BLVR-A) generates BR by the subsequent conversion of BV. BLVR-A is a fascinating protein that possesses a classical protein kinase domain, which is activated in response to BV binding to its enzymatic site and initiates the downstream mitogen-activated protein kinases (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways. This links BLVR-A activity to cell growth and survival pathways. BLVR-A also contains a bZip DNA binding domain and a nuclear export sequence (NES) and acts as a transcription factor to regulate the expression of immune modulatory genes. Here we will discuss the role of heme-related immune response and the potential for targeting the heme system for therapies directed toward hepatitis and cancer.

Enhanced oral absorption of insulin using colon-specific nanoparticles co-modified with amphiphilic chitosan derivatives and cell-penetrating peptides

In this study, amphipathic chitosan derivative (ACS) and cell-penetrating peptide (CPP) co-modified colon-specific nanoparticles (CS-CPP NPs) were prepared and evaluated to improve the oral bioavailability of protein and peptide drugs. ACS modification was harnessed to protect CPPs from degradation in the stomach and small intestine after oral administration and achieve colon-specific drug delivery. After CS-CPP NPs reached the colon, ACSs on the surface of the NPs were gradually degraded and CPPs were exposed to bring into play the penetration efficacy in the colon epithelium. Herein, we synthesized four types of ACSs (TOCS, TDCS, TPCS and TSCS) and adopted three types of CPPs (Tat, Penetratin and R8) to prepare NPs (TOCS-Tat NPs, TDCS-Tat NPs, TPCS-Tat NPs, TSCS-Tat NPs, TDCS-Pen NPs and TDCS-R8 NPs). The study of the protective effects of ACS upon Tat showed that the modification of ACS exerted favourable protection upon Tat in the stomach and small intestine. ACS degradation in the colon was indirectly determined in the viscosity method, which indicated that ACS could be gradually degraded in the colon. Using Caco-2 cell monolayers as cell models, it was found that the cellular uptake amount and transcellular transportation performance of CS-CPP NPs were much enhanced compared with those of TDCS NPs and PVA NPs. With Bama mini-pigs as animal models, the pharmacodynamic study demonstrated that the hypoglycemic effect for insulin-loaded TDCS-Tat NPs was more significant than that for TDCS NPs, lowering the blood glucose by 40%. The pharmacokinetic study indicated that the AUC and Cmax for TDCS-Tat NPs were respectively increased by 1.45 times and 1.82 times compared with those of TDCS NPs. In conclusion, CS-CPP NPs as vehicles for colon-specific drug delivery systems may be an efficient approach to improve the oral absorption of protein and peptide drugs.

Nanoparticles: Oral Delivery for Protein and Peptide Drugs

Protein and peptide drugs have many advantages, such as high bioactivity and specificity, strong solubility, and low toxicity. Therefore, the strategies for improving the bioavailability of protein peptides are reviewed, including chemical modification of nanocarriers, absorption enhancers, and mucous adhesion systems. The status, advantages, and disadvantages of various strategies are systematically analyzed. The systematic and personalized design of various factors affecting the release and absorption of drugs based on nanoparticles is pointed out. It is expected to design a protein peptide oral delivery system that can be applied in the clinic.

Preparation, characterization, and pharmacokinetics of liposomal docetaxel for oral administration

A docetaxel (DTX) liposomal formulation composed of egg phosphatidylcholine, sodium deoxycholate, and stearylamine was developed. Eudragit (0.5%) was coated to deliver the drug to the region between the distal small intestine and the colon. Lyophilized trehalose and mannitol were used as cryoprotectants because they preserve the particle integrity and good appearance. In vitro release studies showed that the amount of drug released from the coated liposomes was low in solution 1, which simulated the pH condition of the stomach. Especially during the average gastric emptying time, the amount of drug released decreased when Eudragit was added. The plasma DTX concentration was evaluated in pharmacokinetic studies. The plasma drug concentration after intravenous (i.v.) administration decreased rapidly within 120 min. Free DTX formulated using Tween 80 and the lyophilized Eudragit-coated liposomal formulation were compared after oral administration. The oral liposomal formulation had a longer half-life (t_1/2) and three-fold higher oral bioavailability. Thus, lyophilized Eudragit-coated liposomal DTX could be a promising therapy for various solid tumors to improve patient convenience and quality of life.

Eudragit S100-Coated Chitosan Nanoparticles Co-loading Tat for Enhanced Oral Colon Absorption of Insulin

In order to improve oral absorption of insulin, especially the absorption at the colon, Eudragit S100® (ES)-coated chitosan nanoparticles loading insulin and a trans-activating transcriptional peptide (Tat) were employed as the vehicle. In vitro releases of insulin and Tat from ES-coated chitosan nanoparticles had a pH-dependant characteristic. A small amount of the contents was released from the coated nanoparticles at pH 1.2 simulated gastric fluid, while a fairly fast and complete release was observed in pH 7.4 medium. Caco-2 cell was used as the model of cellular transport and uptake studies. The results showed that the cellular transport and uptake of insulin for ES-coated chitosan nanoparticles co-loading insulin and Tat (ES-Tat-cNPs) were about 3-fold and 4-fold higher than those for the nanoparticles loading only insulin (ES-cNPs), respectively. The evaluations in vivo of ES-Tat-cNPs were conducted on diabetic rats and normal minipigs, respectively. The experimental results on rats revealed that the pharmacodynamical bioavailability of ES-Tat-cNPs had 2.16-fold increase compared with ES-cNPs. After oral administration of nanoparticle suspensions to the minipigs, insulin bioavailability of ES-Tat-cNPs was 1.73-fold higher than that of ES-cNPs, and the main absorption site of insulin was probably located in the colon for the two nanoparticles. In summary, this report provided an exploratory means for the improvement of oral absorption of insulin.

In-vitro evaluation of enteric coated insulin tablets containing absorption enhancer and enzyme inhibitor

Objectives

The aim of this study was to develop an enteric coated insulin tablet formulation using polymers, absorption enhancer and enzyme inhibitor, which protect the tablets in acidic pH and enhance systemic bioavailability.

Methods

In this study, the influence of coating by cellulose acetate hydrogen phthalate solution and chosen excipients on Glut-4 transporter translocation in C2C12 skeletal muscle cells was examined. Following the determination of optimum number of coating layers, two dissolution buffers such as 0.01 m hydrochloric acid, pH 2, and 50 mm phosphate, pH 7.4, were employed to determine the in-vitro release of insulin.

Key findings

Insulin was protected by the coating during the dissolution process. Five (5-CL) coating layers and eight (8-CL) coating layers had minimal insulin release in hydrochloric acid, but not three (3-CL) coating layers. Glut-4 translocation in C2C12 cells was promoted by the chosen excipients. No detrimental metabolic effects were observed in these cells.

Conclusion

To date, limited studies combine the overall effectiveness of multiple excipients. Our study showed that the coated tablets have an immediate release effect in phosphate buffer. In Glut-4 translocation assay, insulin was still functional after releasing from the tablet. Such tablet formulation can be potentially beneficial to type 1 diabetes patients.

Approaches for enhancing oral bioavailability of peptides and proteins

Oral delivery of peptide and protein drugs faces immense challenge partially due to the gastrointestinal (GI) environment. In spite of considerable efforts by industrial and academic laboratories, no major breakthrough in the effective oral delivery of polypeptides and proteins has been accomplished. Upon oral administration, gastrointestinal epithelium acts as a physical and biochemical barrier for absorption of proteins resulting in low bioavailability (typically less than 1-2%). An ideal oral drug delivery system should be capable of (a) maintaining the integrity of protein molecules until it reaches the site of absorption, (b) releasing the drug at the target absorption site, where the delivery system appends to that site by virtue of specific interaction, and (c) retaining inside the gastrointestinal tract irrespective of its transitory constraints. Various technologies have been explored to overcome the problems associated with the oral delivery of macromolecules such as insulin, gonadotropin-releasing hormones, calcitonin, human growth factor, vaccines, enkephalins, and interferons, all of which met with limited success. This review article intends to summarize the physiological barriers to oral delivery of peptides and proteins and novel pharmaceutical approaches to circumvent these barriers and enhance oral bioavailability of these macromolecules.

Oral delivery of macromolecules: rationale underpinning Gastrointestinal Permeation Enhancement Technology (GIPET)

Oral delivery of macromolecular drugs, particularly peptides and proteins, is the focus of many academic and industrial laboratories. Armed with an increased understanding of the structure and regulation of intestinal epithelial junctional complexes of the paracellular barrier, the development of permeation enhancement technology initially focused on the specific and reversible opening of tight junctions in order to enable oral delivery. Despite intense research, none of these specific tight junction-opening technologies has yet been approved in an oral drug product, likely because of poor efficacy. Less specific enhancer technologies with a long history of safe use in man have additional surfactant-like effects on the transcellular pathway that lead to improved efficacy. These are likely to be the first to market for selected poorly permeable peptides. This review presents a summary of some approaches taken to intestinal permeation enhancement and explores in detail the oral delivery system developed by Merrion Pharmaceuticals, Gastrointestinal Permeation Enhancement Technology (GIPET).

Oral delivery of peptides and proteins using lipid-based drug delivery systems

INTRODUCTION

In order to successfully develop lipid-based drug delivery systems (DDS) for oral administration of peptides and proteins, it is important to gain an understanding of the colloid structures formed by these DDS, the mode of peptide and protein incorporation as well as the mechanism by which intestinal absorption of peptides and proteins is promoted.

AREAS COVERED

The present paper reviews the literature on lipid-based DDS, employed for oral delivery of peptides and proteins and highlights the mechanisms by which the different lipid-based carriers are expected to overcome the two most important barriers (extensive enzymatic degradation and poor transmucosal permeability). This paper also gives a clear-cut idea about advantages and drawbacks of using different lipidic colloidal carriers ((micro)emulsions, solid lipid core particles and liposomes) for oral delivery of peptides and proteins.

EXPERT OPINION

Lipid-based DDS are safe and suitable for oral delivery of peptides and proteins. Significant progress has been made in this area with several technologies on clinical trials. However, a better understanding of the mechanism of action in vivo is needed in order to improve the design and development of lipid-based DDS with the desired bioavailability and therapeutic profile.

Oral colon delivery of insulin with the aid of functional adjuvants

Oral colon delivery is currently considered of importance not only for the treatment of local pathologies, such as primarily inflammatory bowel disease (IBD), but also as a means of accomplishing systemic therapeutic goals. Although the large bowel fails to be ideally suited for absorption processes, it may indeed offer a number of advantages over the small intestine, including a long transit time, lower levels of peptidases and higher responsiveness to permeation enhancers. Accordingly, it has been under extensive investigation as a possible strategy to improve the oral bioavailability of peptide and protein drugs. Because of a strong underlying rationale, most of these studies have focused on insulin. In the present review, the impact of key anatomical and physiological characteristics of the colon on its viability as a protein release site is discussed. Moreover, the main formulation approaches to oral colon targeting are outlined along with the design features and performance of insulin-based devices.

Colon-targeted cell-permeable NFκB inhibitory peptide is orally active against experimental colitis

For the purpose of development of orally active peptide therapeutics targeting NFκB for treatment of inflammatory bowel disease (IBD), two major barriers in oral delivery of therapeutic peptides, metabolic lability and tissue impermeability, were circumvented by introduction of a colon-targeted delivery system and cell permeable peptides (CPP) to NFκB inhibitory peptides (NIP). Suppression of NFκB activation was compared following treatment with various CPP conjugated NIPs (CPP-NIP). The most potent CPP-NIP was loaded in a capsule coated with a colon specific polymer, which was administered orally to colitic rats. The anti-inflammatory activity of the colon-targeted CPP-NIP was evaluated by measuring inflammatory indices in the inflamed colonic tissue. For confirmation of the local action of the CPP-NIP, the same experiment was done after rectal administration. Tissue permeability of the CPP-NIP was examined microscopically and spectrophotometrically using FITC-labeled CPP-NIP (CPP-NIP-FITC). NEMO binding domain peptide (NBD, TALDWSWLQTE) fused with a cell permeable peptide CTP (YGRRARRRARR), CTP-NBD, was most potent in inhibiting NFκB activity in cells. Colon-targeted CTP-NBD, but not colon-targeted NBD and CTP-NBD in an enteric capsule, ameliorated the colonic injury, which was in parallel with decrease in MPO activity and the levels of inflammatory mediators. Intracolonic treatment with CTP-NBD alleviated rat colitis and improved all the inflammatory indicators. CTP-NBD-FITC was detected at much greater level in the inflamed tissue than was NBD-FITC. Taken together, introduction of cell permeability and colon targetability to NIP may be a feasible strategy for an orally active peptide therapy for treatment of IBD.

Novel salicylazo polymers for colon drug delivery: dissolving polymers by means of bacterial degradation

Novel azo polymers were prepared for colonic drug delivery with a release mechanism based on structural features of azo derivatives designed for rapid bacterial degradation leading to soluble polymers. Two Salicylazo derivatives were prepared and conjugated as side chains at different ratios to methacrylic acid-methyl methacrylate copolymers (Eudragits). The azo compounds were designed to have a hydrophilic and a hydrophobic part on opposite sides of the azo bond. Upon reduction of the azo bonds, the hydrophobic part is released, resulting in a more water soluble polymer. The solubility of the polymeric films was studied relative to Eudragit S known to dissolve toward the end of the small intestine. One of the two azo derivatives prepared gave rise to polymers, which showed reduced solubility relative to Eudragit S. These polymers were subjected to reduction tests in anaerobic rat cecal suspensions by following the release of the hydrophobic product. Reduction rate was found to be rapid, comparable to that of Sulfasalazine. Studies on the azopolymeric films in anaerobic rat cecal suspensions, showed that these polymers dissolve faster than in sterilized suspensions. Solid dosage forms may be coated with these polymers to provide an efficient delivery system to the colon with a rapid release mechanism.

Synthesis and anaerobic biodegradation of indomethacin-conjugated cellulose ethers used for colon-specific drug delivery

Water soluble cellulose ethers, including methylcellulose and two hydroxyethylcelluloses with different molecular weights, were conjugate with indomethacin at room temperature. The chemical structures of the conjugates were characterized by FTIR, (1)H NMR and UV-vis spectroscopy. The results confirmed that different amounts of IND residues were covalently bonded to cellulose ether backbones through ester linkages. Their anaerobic biodegradation in colonic fermentation was investigated by gel permeation chromatography, gas chromatography and UV-vis spectroscopy. These conjugates were found to have different biodegradabilities, depending on the cellulose ether used and the amount of conjugated indomethacin residues. In vitro release experiments showed that hydroxyethylcellulose-based conjugates with low IND residues content could exhibit a sustained drug release behavior in colonic fermentation and were stable in the simulated media of the stomach and small intestine. Therefore, they are promising candidates for future applications in colon-specific drug delivery.

Colonic treatments and targets: issues and opportunities

The colon provides a plethora of therapeutic opportunities. There are multiple disease targets, drug molecules, and colon-specific delivery systems to be explored. Clinical studies highlight the potential for systemic delivery via the colon, and the emerging data on the levels of cell membrane transporters and metabolic enzymes along the gut could prove advantageous for this. Often efflux transporters and metabolic enzyme levels are lower in the colon, suggesting a potential for improved bioavailability of drug substrates at this site. The locoregional distribution of multiple metabolic enzymes (including cytochromes), efflux transporters (including P-glycoprotein and breast cancer resistance proteins), and influx transporters (including the solute carrier family) along the intestine is summarized. Local delivery to the colonic mucosa remains a valuable therapeutic option. New therapies that target inflammatory mediators could improve the treatment of inflammatory bowel disease, and old and new anticancer molecules could, when delivered topically, prove to be beneficial adjuncts to the current systemic or surgical treatments. New issues such as pharmacogenomics, chronotherapeutics, and the delivery of prebiotics and probiotics are also discussed in this review. Targeting drugs to the colon utilizes various strategies, each with their advantages and flaws. The most promising systems are considered in the light of the physiological data which influence their in vivo behavior.

Cyclomaltoheptaose mixed esters of anti-inflammatory drugs and short-chain fatty acids and study of their enzymatic hydrolysis in vitro

In an effort to enhance the drug-loading capacity of cyclomaltoheptaose (beta-cyclodextrin, betaCD) and to combine the function of anti-inflammatory drugs with short-chain fatty acids (SCFA), ternary esters incorporating seven copies of an anti-inflammatory drug and 14 copies of a SCFA onto a beta-cyclodextrin core were designed and prepared. Acetic, propionic, or butyric esters were introduced at secondary OH groups, and ibuprofen, flurbiprofen, or felbinac was attached to primary OH groups through ester bonds. Heptakis[2,3-di-O-butanoyl-6-O-2-(biphenyl-4-yl)-ethanoyl]-cyclomaltoheptaose was very stable in aqueous and esterase solution. It was hydrolyzed by alpha-amylase (4 units/mL) with t(1/2) value of 18h. The total released amount of biphenyl acetic acid was 38% after 24h when the esterase was added after the alpha-amylase hydrolysis. The present results suggest that these nine betaCD conjugates may release the anti-inflammatory drug in the colonic contents.

Efficient tumor targeting of hydroxycamptothecin loaded PEGylated niosomes modified with transferrin

The aim of the present report was to exploit the possibility of combination of the stealth action by polyethylene glycol cyanoacrylate-co-hexadecyl cyanoacrylate (PEG-PHDCA) modified niosomes and active targeting function of transferrin (Tf) by transferrin receptor-mediated endocytosis to promote drug delivery to solid tumor following intravenous administration with hydroxycamptothecin (HCPT) as model drug. HCPT-loaded PEG-niosomes (PEG-NS) were prepared by thin-film hydration and ultrasound method; the periodate-oxidated Tf was coupled to terminal amino group of PEG to produce the active targeting vesicles with average diameters of 116 nm. The uptake of Tf-PEG-NS into KB cells was concentration and time dependent, which could be inhibited by low temperature and free Tf, indicating that the endocytosis process was energy-driven and receptor specific. Compared with HCPT injection, non-stealth niosomes and PEG-NS, Tf-PEG-NS demonstrated the strongest cytotoxicity to three carcinomatous cell lines (KB, K562 and S180 cells), the greatest intracellular uptake especially in nuclei, the highest tumor concentration and largest area under the intratumoral hydroxycamptothecin concentration curve, as well as the most powerful anti-tumor activity with the inhibition rate of 71% against S180 tumor in mice. The results showed that the transferrin modified PEGylated niosomes could be one of the promising solutions to the delivery of anti-tumor drugs to tumor.