In Situ Polymerization of Zwitterions on Therapeutic Proteins to Enable Their Effective Oral Delivery

Template-Free Self-Assembly of Hollow Microtubular Covalent Organic Frameworks for Oral Delivery of Insulin

Covalent organic frameworks (COFs) have demonstrated versatile application potential since their discovery. Although the structure of COFs is orderly arranged, the synthesis of controllable macrostructures still faces challenges. Herein, we report, to our knowledge, the first template-free self-assembled COF-18 Å hollow microtubule (MT-COF-18 Å) structure and its use for insulin delivery that exhibits high loading capacity, gastroresistance, and glucose-responsive properties. The hollow MT-COF-18 Å was achieved by a template-free method benefiting from the mixed solvents of mesitylene and dioxane. The formation mechanism and morphology changes with insulin loading and release were observed. In Caco-2 cells, the transferrin-coated system demonstrated enhanced insulin cellular uptake and transcellular transport, which indicated great potential for oral applications. Additionally, the composites presented sustained glycemic control and effective insulin blood concentrations without noticeable toxicity in diabetic rats. This work shows that hollow microtubular COFs hold great promise in loading and delivery of biomolecules.

Ursodeoxycholic Acid-Decorated Zwitterionic Nanoparticles for Orally Liver-Targeted Close-Looped Insulin Delivery

Oral insulin therapies targeting the liver and further simulating close-looped secretion face significant challenges due to multiple trans-epithelial barriers. Herein, ursodeoxycholic acid (UDCA)-decorated zwitterionic nanoparticles (NPs) (UC-CMs@ins) are designed to overcome these barriers, target the liver, and respond to glycemia, thereby achieving oral one-time-per-day therapy. UC-CMs@ins show excellent mucus permeability through the introduction of zwitterion (carboxy betaine, CB). Furthermore, UC-CMs@ins possess superior cellular internalization via proton-assisted amino acid transporter 1 (PAT1, CB-receptor) and apical sodium-dependent bile acid transporter (ASBT, UDCA-receptor) pathways. Moreover, UC-CMs@ins exhibit excellent endolysosomal escape ability and improve the basolateral release of insulin into the bloodstream via the ileal bile acid-binding protein and the heteromeric organic solute transporter (OSTα- OSTβ) routes compared with non-UDCA-decorated C-CMs@ins. Therefore, CB and UDCA jointly overcome mucus and intestinal barriers. Additionally, UC-CMs@ins prevent insulin degradation in the gastrointestinal tract for crosslinked structure, improve insulin accumulation in the liver for UDCA introduction, and effectively regulate glycemia for "closed-loop" glucose control. Surprisingly, oral ingestion of UC-CMs@ins shows a superior effect on glycemia (≈22 h, normoglycemia) and improves postprandial glycemic levels in diabetic mice, illustrating the enormous potential of the prepared NPs as a platform for oral insulin administration in diabetes treatment.

Eyedrop delivery of therapeutic proteins with zwitterionic polymers to treat dry age-related macular degeneration

In clinics, therapeutic proteins are commonly used to treat retinal diseases through intraocular injection, the treatment which suffers from rather low patient compliance. Topical administration (e.g. eye-drops) of large molecule drugs remains a major challenge due to the presence of various barriers in the eye. In this study, zwitterion-grafted chitosan (CS-ZW) was developed and then self-assembled with protein therapeutics including adalimumab (ADA) or catalase (CAT) for the treatment of dry age-related macular degeneration (dAMD) via topical eyedrops. Since CS-ZW can cross the mucus layer and open the tight junctions between epithelial cells, their delivered therapeutic proteins can be shuttled across the ocular barriers to reach the diseased site in the fundus. CS-ZW/ADA eyedrops delivering ADA to bind TNF-α in the fundus achieved a similar therapeutic effect to intravitreal ADA injection in a mouse dAMD model. In addition, the therapeutic effect was further improved by combining eyedrop formulations of CS-ZW/ADA and CS-ZW/CAT, the latter of which can clear reactive oxygen species (ROS) in the lesion to further assist dAMD treatment. Our work provides a simple and effective delivery vehicle that can non-invasively treat fundus diseases such as dAMD, showing potential advantages in reducing side effects associated with intraocular injection and improving patient compliance.

Oral Nanomedicine: Challenges and Opportunities

Compared to injection administration, oral administration is free of discomfort, wound infection, and complications and has a higher compliance rate for patients with diverse diseases. However, oral administration reduces the bioavailability of medicines, especially biologics (e.g., peptides, proteins, and antibodies), due to harsh gastrointestinal biological barriers. In this context, the development and prosperity of nanotechnology have helped improve the bioactivity and oral availability of oral medicines. On this basis, first, the biological barriers to oral administration are discussed, and then oral nanomedicine based on organic and inorganic nanomaterials and their biomedical applications in diverse diseases are reviewed. Finally, the challenges and potential opportunities in the future development of oral nanomedicine, which may provide a vital reference for the eventual clinical transformation and standardized production of oral nanomedicine, are put forward.

Materials and structure of polysaccharide-based delivery carriers for oral insulin: A review

Diabetes mellitus is a chronic metabolic disease that affects >500 million patients worldwide. Subcutaneous injection of insulin is the most effective treatment at present. However, regular needle injections will cause pain, inflammation, and other adverse consequences. In recent years, significant progress has been made in non-injectable insulin preparations. Oral administration is the best way of administration due to its simplicity, convenience, and good patient compliance. However, oral insulin delivery is hindered by many physiological barriers in the gastrointestinal tract, resulting in the low relative bioavailability of direct oral insulin delivery. To improve the relative bioavailability, a variety of insulin delivery vectors have been developed. Polysaccharides are used to achieve safe and effective insulin loading due to their excellent biocompatibility and protein affinity. The functional characteristics of polysaccharide-based delivery carriers, such as pH responsiveness, mucosal adhesion, and further functionalization modifications, enhance the gastrointestinal absorption and bioavailability of insulin. This paper reviews the materials and structures of oral insulin polysaccharide-based carriers, providing ideas for further improving the relative bioavailability of oral insulin.

Betaine-Based and Polyguanidine-Inserted Zwitterionic Micelle as a Promising Platform to Conquer the Intestinal Mucosal Barrier

Developing nanocarriers for oral drug delivery is often hampered by the dilemma of balancing mucus permeation and epithelium absorption, since huge differences in surface properties are required for sequentially overcoming these two processes. Inspired by mucus-penetrating viruses that universally possess a dense charge distribution with equal opposite charges on their surfaces, we rationally designed and constructed a poly(carboxybetaine)-based and polyguanidine-inserted cationic micelle platform (hybrid micelle) for oral drug delivery. The optimized hybrid micelle exhibited a great capacity for sequentially overcoming the mucus and villi barriers. It was demonstrated that a longer zwitterionic chain was favorable for mucus diffusion for hybrid micelles but not conducive to cellular uptake. In addition, the significantly enhanced internalization absorption of hybrid micelles was attributed to the synergistic effect of polyguanidine and proton-assisted amine acid transporter 1 (PAT1). Moreover, the retrograde pathway was mainly involved in the intracellular transport of hybrid micelles and transcytosis delivery. Furthermore, the prominent intestinal mucosa absorption in situ and in vivo liver distribution of the oral hybrid micelle were both detected. The results of this study indicated that the hybrid micelles were capable of conquering the intestinal mucosal barrier, having a great potential for oral application of drugs with poor oral bioavailability.

Challenges and opportunities in delivering oral peptides and proteins

INTRODUCTION

Rapid advances in bioengineering enable the use of complex proteins as therapeutic agents to treat diseases. Compared with conventional small molecule drugs, proteins have multiple advantages, including high bioactivity and specificity with low toxicity. Developing oral dosage forms with active proteins is a route to improve patient compliance and significantly reduce production costs. However, the gastrointestinal environment remains a challenge to this delivery path due to enzymatic degradation, low permeability, and weak absorption, leading to reduced delivery efficiency and poor clinical outcomes.

AREAS COVERED

This review describes the barriers to oral delivery of peptides and complex proteins, current oral delivery strategies utilized and the opportunities and challenges ahead to try and circumvent these barriers. Oral protein drugs on the market and clinical trials provide insights and approaches for advancing delivery strategies.

EXPERT OPINION

Although most current studies on oral protein delivery rely on in vitro and in vivo animal data, the safety and limitations of the approach in humans remain uncertain. The shortage of clinical data limits the development of new or alternative strategies. Therefore, designing appropriate oral delivery strategies remains a significant challenge and requires new ideas, innovative design strategies and novel model systems.

A nano-delivery system based on preventing degradation and promoting absorption to improve the oral bioavailability of insulin

Oral insulin delivery can improve patient compliance and simulate the portal-peripheral insulin concentration gradient produced by endogenous insulin, so oral insulin delivery has a broad prospect. However, some characteristics of the gastrointestinal tract, lead to low oral bioavailability. Therefore, a "ternary mutual-assist" nano-delivery system based on poly(lactide-co-glycolide) (PLGA) as the backbone combined with ionic liquids (IL) and vitamin B12-chitosan (VB12-CS) was constructed in this study, the protein protection performance of IL improves the room temperature stability of the loaded insulin during nanocarrier preparation, transportation and storage to a certain extent, and the protein protection function of IL combined with the slow degradation property of PLGA and the pH-responsive function of VB12-CS to prevent the degradation of insulin in the gastrointestinal tract. In addition, the mucosal adhesion function of VB12-CS, VB12 receptor- and clathrin-mediated transcellular transport involving VB12-CS and IL, and paracellular transport mediated by IL and CS can be combined to improve the intestinal epithelial transport efficiency of insulin, thus, the nanocarrier has stronger preventing degradation and promoting absorption effects. Pharmacodynamic studies showed that after oral administration of VB12-CS-PLGA@IL@INS NPs to diabetic mice, the blood glucose level decreased to about 13 mmol/L, below the critical point of 16.7 mmol/L, and the blood glucose reached a normal level, which was 0.4 times of the blood glucose value before administration, its relative pharmacological bioavailability was 31.8 %, higher than the general nanocarriers (10-20 %) and more beneficial to the clinical transformation of oral insulin.