Nitrilotriacetic Acid-Functionalized Glucose-Responsive Complex Micelles for the Efficient Encapsulation and Self-Regulated Release of Insulin

Noncovalent PEGylation of protein and peptide therapeutics

Clinical applications of protein therapeutics-an advanced generation of drugs characterized by high biological specificity-are rapidly expanding. However, their development is often impeded by unfavorable pharmacokinetic profiles and largely relies on the use of drug delivery systems to prolong their in vivo half-life and suppress undesirable immunogenicity. Although a commercially established PEGylation technology based on protein conjugation with poly(ethylene glycol) (PEG)-protective steric shield resolves some of the challenges, the search for alternatives continues. Noncovalent PEGylation, which mainly relies on multivalent (cooperative) interactions and high affinity (host-guest) complexes formed between protein and PEG offers a number of potential advantages. Among them are dynamic or reversible protection of the protein with minimal loss of biological activity, drastically lower manufacturing costs, "mix-and-match" formulations approaches, and expanded scope of PEGylation targets. While a great number of innovative chemical approaches have been proposed in recent years, the ability to effectively control the stability of noncovalently assembled protein-PEG complexes under physiological conditions presents a serious challenge for the commercial development of the technology. In an attempt to identify critical factors affecting pharmacological behavior of noncovalently linked complexes, this Review follows a hierarchical analysis of various experimental techniques and resulting supramolecular architectures. The importance of in vivo administration routes, degradation patterns of PEGylating agents, and a multitude of potential exchange reactions with constituents of physiological compartments are highlighted. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Molecular Docking-Guided Design on Glucose-Responsive Nanoparticles for Microneedle Fabrication and "Three-Meal-per-Day" Blood-Glucose Regulation

It was greatly significant, but difficult, to develop stimulus-responsive polymeric nanoparticles with efficient protein-loading and protein-delivering properties. Crucial obstacles were the ambiguous protein/nanoparticle-interacting mechanisms and the corresponding inefficient trial-and-error strategies, which brought large quantities of experiments in design and optimization. In this work, a molecular docking-guided universal "segment-functional group-polymer" process was proposed to simplify the previous laborious experimental step. The insulin-delivering glucose-responsive polymeric nanoparticles for diabetic treatments were taken as the examples. The molecular docking study obtained insights from the insulin/segment interactions. It was then experimentally confirmed in six functional groups for insulin-loading performances of their corresponding polymers. The optimization formulation was further proved effective in blood-glucose stabilization on the diabetic rats under the "three-meal-per-day" mode. It was believed that the molecular docking-guided designing process was promising in the protein-delivering field.

An Engineered Nanosugar Enables Rapid and Sustained Glucose-Responsive Insulin Delivery in Diabetic Mice

Glucose-responsive insulin-delivery platforms that are sensitive to dynamic glucose concentration fluctuations and provide both rapid and prolonged insulin release have great potential to control hyperglycemia and avoid hypoglycemia diabetes. Here, biodegradable and charge-switchable phytoglycogen nanoparticles capable of glucose-stimulated insulin release are engineered. The nanoparticles are "nanosugars" bearing glucose-sensitive phenylboronic acid groups and amine moieties that allow effective complexation with insulin (≈95% loading capacity) to form nanocomplexes. A single subcutaneous injection of nanocomplexes shows a rapid and efficient response to a glucose challenge in two distinct diabetic mouse models, resulting in optimal blood glucose levels (below 200 mg dL^-1 ) for up to 13 h. The morphology of the nanocomplexes is found to be key to controlling rapid and extended glucose-regulated insulin delivery in vivo. These studies reveal that the injected nanocomplexes enabled efficient insulin release in the mouse, with optimal bioavailability, pharmacokinetics, and safety profiles. These results highlight a promising strategy for the development of a glucose-responsive insulin delivery system based on a natural and biodegradable nanosugar.

Advances in the Design of Phenylboronic Acid-Based Glucose-Sensitive Hydrogels

Diabetes, characterized by an uncontrolled blood glucose level, is the main cause of blindness, heart attack, stroke, and lower limb amputation. Glucose-sensitive hydrogels able to release hypoglycemic drugs (such as insulin) as a response to the increase of the glucose level are of interest for researchers, considering the large number of diabetes patients in the world (537 million in 2021, reported by the International Diabetes Federation). Considering the current growth, it is estimated that, up to 2045, the number of people with diabetes will increase to 783 million. The present work reviews the recent developments on the hydrogels based on phenylboronic acid and its derivatives, with sensitivity to glucose, which can be suitable candidates for the design of insulin delivery systems. After a brief presentation of the dynamic covalent bonds, the design of glucose-responsive hydrogels, the mechanism by which the hypoglycemic drug release is achieved, and their self-healing capacity are presented and discussed. Finally, the conclusions and the main aspects that should be addressed in future research are shown.

Glucose-responsive nanoparticles designed via a molecular-docking-driven method for insulin delivery

Nocturnal blood glucose regulation was one of the key challenges in diabetic treatments. However, development of the smart insulin complexes with mild and glucose-responsive delivering performances was mostly relied on experience of the senior researchers and numerous confirmation experiments. In this work, a series of bioinspired fatty-acid-modified glucose-responsive insulin-delivering polymeric nanoparticles were designed. The molecular docking technique was utilized to efficiently screen the fatty-acid-derived functional groups. The results provided the basis for polymer functionalization and simplified the optimization experiments. For the optimized formulation (C10MS), insulin-loaded C10MS successfully fulfilled the nocturnal-glycemic-controlling requirement of the diabetic rats with lower occurrence of hypoglycemia than the conventional insulin injection schemes. Such formulation also possessed good biocompatibility with the moderate elimination kinetics in vivo, which matched the demand of bio-safety in the daily treatments. Overall, this work opened up a new path for efficient design of functional polymeric materials.

Biomedical Applications of polymeric micelles in the treatment of diabetes mellitus: Current success and future approaches

INTRODUCTION

Diabetes mellitus (DM) is the most common metabolic disease and multifactorial, harming patients worldwide. Extensive research has been carried out in the search for novel drug delivery systems offering reliable control of glucose levels for diabetics, aiming at efficient management of DM.

AREAS COVERED

Polymeric micelles (PMs) as smart drug delivery nanocarriers are discussed, focusing on oral drug delivery applications for the management of hyperglycemia. The most recent approaches used for the preparation of smart PMs employ molecular features of amphiphilic block copolymers (ABCs), such as stimulus sensitivity, ligand conjugation, and as a more specific example the ability to inhibit islet amyloidosis.

EXPERT OPINION

PMs provide a unique platform for self-regulated or spatiotemporal drug delivery, mimicking the working mode of pancreatic islets to maintain glucose homeostasis for prolonged periods. This unique characteristic is achieved by tailoring the functional chemistry of ABCs considering the physicochemical traits of PMs, including sensing capabilities, hydrophobicity, etc. In addition, the application of ABCs for the inhibition of conformational changes in islet amyloid polypeptide garnered attention as one of the root causes of DM. However, research in this field is limited and further studies at the clinical level are required.

Prevent Drug Leakage via the Boronic Acid Glucose-Insensitive Micelle for Alzheimer's Disease Combination Treatment

Boronic acid (BA) materials have been widely applied to glucose and oxidative stress-sensitive drug delivery for the treatment of cancer, diabetes, and Alzheimer's disease (AD). There are completely various BA-sensitive delivery conditions in different diseases. BA materials in the treatment of diabetes show better performance at a high-glucose environment than normal. In contrast, the concentration of glucose in the brain is much lower than that in the blood of AD patients. Hence, the typical glucose and oxidative stress dual-sensitive BA materials inevitably encounter drug leakage in circulation in AD. Attempts to decrease the glucose-sensitive capacity of BA materials are extremely essential for AD drug delivery. In this study, the epoxy group (electron-donating group) was introduced to increase the pKa values of BA materials by increasing the electron cloud density, and thus, the glucose-insensitive micelle (GIM) was obtained. The treatment effect and the synergism mechanism of the drug-loaded GIM micelle were studied on senescence-accelerated mouse prone 8 mice. This work provided excellent antioxidant drugs (vitamin E succinate, melatonin, and quercetin) and a glucose metabolism drug (insulin) loaded in GIM micelle for AD treatment. The discovery of the combination mechanism is enormously valuable for AD clinical research.

Glucose and H2O2 Dual-Responsive Nanocomplex Grafted with Insulin Prodrug for Blood Glucose Regulation

Although "closed-loop" smart insulin delivery systems have been extensively investigated, the majority of them suffer from low insulin loading efficiency and slow glucose response. Here, we constructed a novel nanocomplex (NC), which was prepared by electrostatic interaction between negatively charged insulin prodrug nanoparticles (NPs) and positively charged polycaprolactone-polyethylenimine (PCL-PEI) micelles. The insulin prodrug was linked to acetalated dextran (AD) via borate ester bonds to form IAD NPs, and glucose oxidase (GOx) was encapsulated in PCL-PEI micelles. The NC was negatively charged with a high insulin grafting rate (0.473 mg/mg), and in vitro experiments revealed that IAD was sensitive to hyperglycemia and H₂O₂, whereas GOx significantly improved the response to glucose by altering the microenvironment to promote sustained insulin release. Furthermore, compared with free insulin and IAD NPs, subcutaneously injected NCs in diabetic rats had long-term hypoglycemic effects, showing excellent biocompatibility in vitro and in vivo, which had good potential in insulin self-regulation delivery.

An oxidation responsive nano-radiosensitizer increases radiotherapy efficacy by remolding tumor vasculature

As an excellent candidate material for nano-sensitizers, gold nanostructures have shown great potential in radiotherapy. Nevertheless, severe hypoxia and low accumulation of nanomedicine caused by poor perfusion at the tumor site have significantly reduced radiotherapy efficacy. Vascular normalization has gained attention owing to its ability to relieve hypoxia and increase perfusion. The synergistic therapy of tumor vascular normalization and radiotherapy has become a new option to increase anti-cancer efficacy. However, the commonly used strategy of suppressing a single growth factor to induce vascular normalization is limited by tumor compensatory effects. In this work, we developed a strategy to inhibit oxidative stress in tumors by generating chelating agents in response to hydrogen peroxide, thereby inhibiting multi-angiogenic factors simultaneously to normalize blood vessels. Concretely, sodium alginate (SA) reacted with 8-quinoline boric acid (QBA) to form SA-QBA. Then gold nanoparticles (Au NPs) were modified with SA-QBA to obtain Au@SA-QBA. The system was simple in structure and could generate 8HQ in response to H₂O₂in vitro to inhibit oxidative stress and reduce the expression of VEGF, bFGF, and Ang-2. In vivo, the perfusion unit (PU) increased by 78% after Au@SA-QBA treatment, and the coverage of pericytes increased by 32%, which in turn induced vascular normalization. In addition, blood routine and blood biochemical tests confirmed its good biocompatibility and 8HQ was not detected in the supernatant after homogenization of major organs. More importantly, after the synergistic treatment of vascular normalization and radiotherapy (4 Gy), the tumor growth inhibition rate was increased by 38.6% compared to the Au@SA-treated group with negligible side effects to normal tissues.

Biodegradable phenylboronic acid-modified ε-polylysine for glucose-responsive insulin delivery via transdermal microneedles

Microneedles with insulin-loaded glucose-responsive particles are promising to control the blood glucose levels of diabetic patients. In particular, the long-term usage of these microneedles calls for biodegradable and cost-effective particles, which are still large challenges. In this paper, glucose-responsive 4-carboxy-3-fluorophenylboronic acid-grafted ε-polylysine (CFPBA-g-PL) was synthesized to meet these requirements. CFPBA-g-PL had low cytotoxicity, good hemocompatibility and no tissue reaction. The pharmacokinetics of CFPBA-g-PL were also studied. The self-assembled particles of CFPBA-g-PL were prepared via simple ultrasonic treatment. The insulin-loaded particles of CFPBA-g-PL (named INS/GRP-12.8) presented a glucose-responsive insulin delivery performance based on the disassembly-related mechanism in vitro. The INS/GRP-12.8-encapsulated microneedle patch with a uniform morphology and moderate skin penetration performance was prepared via a molding strategy. INS/GRP-12.8 lasted for more than 8 hours of normoglycemia on STZ-induced diabetic SD rats via subcutaneous injection and the INS/GRP-12.8-encapsulated microneedle patch also showed a blood-glucose-level-lowering performance in vivo via transdermal administration.

Bioresponsive Functional Phenylboronic Acid-Based Delivery System as an Emerging Platform for Diabetic Therapy

The glucose-sensitive self-adjusting drug delivery system simulates the physiological model of the human pancreas-secreting insulin and then precisely regulates the release of hypoglycemic drugs and controls the blood sugar. Thus, it has good application prospects in the treatment of diabetes. Presently, there are three glucose-sensitive drug systems: phenylboronic acid (PBA) and its derivatives, concanavalin A (Con A), and glucose oxidase (GOD). Among these, the glucose-sensitive polymer carrier based on PBA has the advantages of better stability, long-term storage, and reversible glucose response, and the loading of insulin in it can achieve the controlled release of drugs in the human environment. Therefore, it has become a research hotspot in recent years and has been developed very rapidly. In order to further carry out a follow-up study, we focused on the development process, performance, and application of PBA and its derivatives-based glucose-sensitive polymer drug carriers, and the prospects for the development of this field.

Recent advances of nanomedicine-based strategies in diabetes and complications management: Diagnostics, monitoring, and therapeutics

Diabetes mellitus (DM) is a metabolic disorder characterized by the presence of chronic hyperglycemia driven by insulin deficiency or resistance, imposing a significant global burden affecting 463 million people worldwide in 2019. This review has comprehensively summarized the application of nanomedicine with accurate, patient-friendly, real-time properties in the field of diabetes diagnosis and monitoring, and emphatically discussed the unique potential of various nanomedicine carriers (e.g., polymeric nanoparticles, liposomes, micelles, microparticles, microneedles, etc.) in the management of diabetes and complications. Novel delivery systems have been developed with improved pharmacokinetics and pharmacodynamics, excellent drug biodistribution, biocompatibility, and therapeutic efficacy, long-term action safety, as well as the improved production methods. Furthermore, the effective nanomedicine for the treatment of several major diabetic complications with significantly improved life qualities of diabetic patients were discussed in detail. Going through the literature review, several critical issues of the nanomedicine-based strategies applications need to be addressed such as stabilities and long-term safety effects in vivo, the deficiency of standard for formulation administration, feasibility of scale-up, etc. Overall, the review provides an insight into the design, advantages and limitations of novel nanomedicine application in the diagnostics, monitoring, and therapeutics of DM.

In Vitro Biological Characterization of Silver-Doped Anodic Oxide Coating on Titanium

Despite the high biocompatibility and clinical effectiveness of Ti-based implants, surface functionalization (with complex osteointegrative/antibacterial strategies) is still required. To enhance the dental implant surface and to provide additional osteoinductive and antibacterial properties, plasma electrolytic oxidation of a pure Ti was performed using a nitrilotriacetic acid (NTA)-based Ag nanoparticles (AgNP)-loaded calcium–phosphate solution. Chemical and structural properties of the surface-modified titanium were assessed using scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) and contact angle measurement. A bacterial adhesion test and cell culture biocompatibility with collagen production were performed to evaluate biological effectiveness of the Ti after the plasma electrolytic process. The NTA-based calcium–phosphate solution with Ag nanoparticles (AgNPs) can provide formation of a thick, porous plasma electrolytic oxidation (PEO) layer enriched in silver oxide. Voltage elevation leads to increased porosity and a hydrophilic nature of the newly formed ceramic coating. The silver-enriched PEO layer exhibits an effective antibacterial effect with high biocompatibility and increased collagen production that could be an effective complex strategy for dental and orthopedic implant development.

Two-in-one strategy: a remineralizing and anti-adhesive coating against demineralized enamel

Tooth enamel is prone to be attacked by injurious factors, leading to a de/remineralization imbalance. To repair demineralized enamel and prevent pulp inflammation caused by biofilm accumulation, measures are needed to promote remineralization and inhibit bacterial adhesion on the tooth surface. An innovative material, poly (aspartic acid)-polyethylene glycol (PASP-PEG), was designed and synthesized to construct a mineralizing and anti-adhesive surface that could be applied to repair demineralized enamel. A cytotoxicity assay revealed the low cytotoxicity of synthesized PASP-PEG. Adsorption results demonstrated that PASP-PEG possesses a high binding affinity to the hydroxyapatite (HA)/tooth surface. In vitro experiments and scanning electron microscopy (SEM) demonstrated a strong capacity of PASP-PEG to induce in situ remineralization and direct the oriented growth of apatite nanocrystals. Energy dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD) and Vickers hardness tests demonstrated that minerals induced by PASP-PEG were consistent with healthy enamel in Ca/P ratio, crystal form and surface micro-hardness. Contact angle tests and bacterial adhesion experiments demonstrated that PASP-PEG yielded a strong anti-adhesive effect. In summary, PASP-PEG could achieve dual effects for enamel repair and anti-adhesion of bacteria, thereby widening its application in enamel repair.

Glucose- and pH-Responsive Supramolecular Polymer Vesicles Based on Host-Guest Interaction for Transcutaneous Delivery of Insulin

Smart insulin delivery platforms having the ability of mimicking pancreatic cells are highly expected for diabetes treatment. Herein, a smart glucose-sensitive insulin delivery platform on the basis of transcutaneous microneedles has been designed. The as-prepared microneedles are composed of glucose- and pH-responsive supramolecular polymer vesicles (PVs) as the drug storage and water soluble polymers as the matrix. The well-defined PVs are constructed from the host-guest inclusion complex between water-soluble pillar[5]arene (WP5) with pH-responsiveness and paraquat-ended poly(phenylboronic acid) (PPBA-G) with glucose-sensitivity. The drug-loaded PVs, including insulin and glucose oxidase (GOx) can quickly respond to elevated glucose level, accompanied by the disassociation of PVs and fast release of encapsulated insulin. Moreover, the insulin release rate is further accelerated by GOx, which generates gluconic acid at high glucose levels, thus decreasing the local pH. Therefore, the host-guest interaction between WP5 and PPBA-G is destroyed and a total structure disassociation of PVs takes place, contributing to a fast release of encapsulated insulin. The in vivo insulin delivery to diabetic rats displays a quick response to hyperglycemic levels and then can fast regulate the blood glucose concentrations to normal levels, which demonstrates that the obtained smart insulin device has a highly potential application in the treatment of diabetes.

Nanochaperones Mediated Delivery of Insulin

Insulin would undergo unfolding and fibrillation under stressed conditions, which may cause serious biotechnological and medical problems. Herein, by mimicking the structure and functions of natural chaperones HSP70s, self-assembled polymeric micelles are used as nanochaperones for the delivery of insulin. The confined hydrophobic domains on the surface of nanochaperones adsorb partially unfolded insulin, inhibiting the aggregation and fibrillation and enhancing the stability of insulin. The bioactivity of insulin is well-reserved after incubation with the nanochaperones at 37 °C for 7 d or heating at 70 °C for 1 h. The stealthy poly(ethylene glycol) chains around the confined domains protect the adsorbed insulin from enzymatic degradation and prolong the circulation time. More importantly, the excellent glucose sensitivity of the hydrophobic domains enables the nanochaperones to release and refold insulin in native form in response to hyperglycemia. This kind of nanochaperone may offer a hopeful strategy for the protection and delivery of insulin.

Glucose and H2O2 dual-sensitive nanogels for enhanced glucose-responsive insulin delivery

Diabetes is a chronic metabolic disorder disease characterized by high blood glucose levels and has become one of the most serious threats to human health. In recent decades, a number of insulin delivery systems, including bulk gels, nanogels, and polymeric micelles, have been developed for the treatment of diabetes. Herein, a kind of glucose and H2O2 dual-responsive polymeric nanogel was designed for enhanced glucose-responsive insulin delivery. The polymeric nanogels composed of poly(ethylene glycol) and poly(cyclic phenylboronic ester) (glucose and H2O2 dual-sensitive groups) were synthesized by a one-pot thiol-ene click chemistry approach. The nanogels displayed glucose-responsive release of insulin and the release rate could be promoted by the incorporation of glucose oxidase (GOx), which generated H2O2 at high glucose levels and H2O2 further oxidizes and hydrolyzes the phenylboronic ester group. The nanogels have characteristics of long blood circulation time, a fast response to glucose, and excellent biocompatibility. Moreover, subcutaneous delivery of insulin to diabetic mice with the insulin/GOx-loaded nanogels presented an effective hypoglycemic effect compared to that of injection of insulin or insulin-loaded nanogels. This kind of nanogel would be a promising candidate for the delivery of insulin in the future.