Nanoparticle and microparticle-based systems for enhanced oral insulin delivery: A systematic review and meta-analysis

Diabetes mellitus (DM) prevalence is rising worldwide. Current therapies comprising subcutaneous insulin injections can cause adverse effects such as lipodystrophy, local reactions like redness and swelling, fluid retention, and allergic reactions. Nanoparticle carriers for oral insulin are groundbreaking compared to existing methods because they are non-invasive treatments, showing operational convenience, controlled release profile, and ability to simulate the physiological delivery route into the bloodstream. These systems improve patient adherence and have demonstrated the potential to lower blood glucose levels in DM. We present a systematic review and meta-analysis aimed at compiling relevant data to pave the way for developing innovative nano- and microparticles for the oral delivery of insulin. Our analysis of 85 articles revealed that the diminution of glucose levels is not proportional to the administered insulin dosage, which ranged from 1 to 120 International Units (IU). The meta-analysis data indicated that 25 IU of encapsulated porcine insulin did not produce a statistically significant outcome (p = 0.93). In contrast, a dosage of 30 IU was efficacious in eliciting an optimal hypoglycemic effect compared to excipient controls. Parameters such as a high degree of encapsulation (~ 90%), particle size (200-400 nm), and polydispersity index (0.086-0.3) are all associated with lower blood glucose levels. These parameters were also significant in the linear regression analysis. Among the excipients employed, chitosan emerged as a prevalent excipient in formulations due to its biocompatible and biodegradable properties and its ability to establish stable polymeric matrices. Even though oral insulin administration is a promising therapeutic method, it cannot guarantee preclinical safety and therapeutic efficacy yet in regulating glucose levels in diabetic conditions.

Synthesis of multi-responsive poly(NIPA-co-DMAEMA)-PBA hydrogel nanoparticles in aqueous solution for application as glucose-sensitive insulin-releasing nanoparticles

Objectives

This study aimed to present an innovative method for synthesizing pH-thermo-glucose responsive poly(NIPA-co-DMAEMA)-PBA hydrogel nanoparticles via single-step aqueous free radical polymerization.

Methods

The synthesis process involved free radical polymerization in an aqueous solution, and the resulting nanoparticles were characterized for their physical and chemical properties by 1H NMR, Dynamic Light Scattering (DLS) and Scanning Electron Microscopy (SEM). Insulin-loaded poly(NIPA-co-DMAEMA)-PBA hydrogel nanoparticles were prepared and evaluated for their insulin capture and release properties at different pH and temperature, in addition to different glucose concentrations, with the release profile of insulin quantitatively evaluated using the Bradford method.

Results

1H NMR results confirmed successful PBA incorporation, and DLS outcomes consistently indicated a transition to a more hydrophobic state above the Lower Critical Solution Temperature (LCST) of NIPA and DMAEMA. While pH responsiveness exhibited variation, insulin release generally increased with rising pH from acidic to neutral conditions, aligning with the anticipated augmentation of anionic PBA moieties and increased hydrogel hydrophilicity. Increased insulin release in the presence of glucose, particularly for formulations with the lowest mol % PBA, along with a slight increase for the highest mol % PBA formulation when increasing glucose from 1 to 4 mg/mL, supported the potential of this approach for nanoparticle synthesis tailored for glucose-responsive insulin release.

Conclusions

This work successfully demonstrates a novel method for synthesizing responsive hydrogel nanoparticles and underscores their potential for controlled insulin release in response to glucose concentrations. The observed pH-dependent insulin release patterns and the influence of PBA content on responsiveness highlight the versatility and promise of this nanoparticle synthesis approach for applications in glucose-responsive drug delivery systems.

Graphical abstract

Poly(NIPA) nanoparticles containing PBA moieties are normally synthesized in two or more steps in the presence of organic solvents. Here we propose a new method for the synthesis of multiresponsive hydrogel poly(NIPA-co-DMAEMA)-PBA nanoparticles in aqueous medium in a single reaction to provide a fast and effective strategy for the production of glucose-responsive multi-systems in aqueous media from free radical polymerization.

Structural changes of layer-by-layer self-assembled starch-based nanocapsules in the gastrointestinal tract: Implications for their M cell-targeting delivery and transport efficiency

Characterizing the structural changes of cell-targeting delivery carriers in gastrointestinal tract (GIT) is crucial for understanding their effectiveness in cell targeting and transport. Herein, RGD peptide-grafted carboxymethyl starch (CMS) and cationic quaternary ammonium starch (QAS) were utilized to fabricate quintet-layered nanocapsules loaded with ovalbumin (OVA). The aim was to improve delivery and transportation efficiency, specifically targeting M cells. The research analyzed the impact of pH and enzyme variations in GIT on the structure of nanocapsules, interactions between carriers and the release behavior of OVA. Results showed that the size of nanocapsules increased from 229.2 to 479.8 nm and the zeta potential decreased from -1.08 to -33.33 mV during oral delivery. This was evident in TEM images, showing a more relaxed core-shell structure. Isothermal titration calorimetry and molecular dynamic simulation indicated that pH changes primarily affected the electrostatic interaction between carriers. Increasing pH led to reduced affinity constants, and around 84.42 % of OVA was successfully delivered to M cells. Moreover, the transport efficiency of nanocapsules to M cells was five times greater than that of Caco-2 cells. This suggests the feasibility of developing a nanocapsules delivery system capable of adapting to pH changes in GIT by regulating electrostatic interactions between carriers.

Polymeric biomaterial-inspired cell surface modulation for the development of novel anticancer therapeutics

Immune cell-based therapies are a rapidly emerging class of new medicines that directly treat and prevent targeted cancer. However multiple biological barriers impede the activity of live immune cells, and therefore necessitate the use of surface-modified immune cells for cancer prevention. Synthetic and/or natural biomaterials represent the leading approach for immune cell surface modulation. Different types of biomaterials can be applied to cell surface membranes through hydrophobic insertion, layer-by-layer attachment, and covalent conjugations to acquire surface modification in mammalian cells. These biomaterials generate reciprocity to enable cell-cell interactions. In this review, we highlight the different biomaterials (lipidic and polymeric)-based advanced applications for cell-surface modulation, a few cell recognition moieties, and how their interplay in cell-cell interaction. We discuss the cancer-killing efficacy of NK cells, followed by their surface engineering for cancer treatment. Ultimately, this review connects biomaterials and biologically active NK cells that play key roles in cancer immunotherapy applications.

Controlled Interfacial Polymer Self-Assembly Coordinates Ultrahigh Drug Loading and Zero-Order Release in Particles Prepared under Continuous Flow

Microparticles are successfully engineered through controlled interfacial self-assembly of polymers to harmonize ultrahigh drug loading with zero-order release of protein payloads. To address their poor miscibility with carrier materials, protein molecules are transformed into nanoparticles, whose surfaces are covered with polymer molecules. This polymer layer hinders the transfer of cargo nanoparticles from oil to water, achieving superior encapsulation efficiency (up to 99.9%). To control payload release, the polymer density at the oil-water interface is enhanced, forming a compact shell for microparticles. The resultant microparticles can harvest up to 49.9% mass fraction of proteins with zero-order release kinetics in vivo, enabling an efficient glycemic control in type 1 diabetes. Moreover, the precise control of engineering process offered through continuous flow results in high batch-to-batch reproducibility and, ultimately, excellent scale-up feasibility.

Surface Adsorption-Mediated Ultrahigh Efficient Peptide Encapsulation with a Precise Ratiometric Control for Type 1 and 2 Diabetic Therapy

A surface adsorption strategy is developed to enable the engineering of microcomposites featured with ultrahigh loading capacity and precise ratiometric control of co-encapsulated peptides. In this strategy, peptide molecules (insulin, exenatide, and bivalirudin) are formulated into nanoparticles and their surface is decorated with carrier polymers. This polymer layer blocks the phase transfer of peptide nanoparticles from oil to water and, consequently, realizes ultrahigh peptide loading degree (up to 78.9%). After surface decoration, all three nanoparticles are expected to exhibit the properties of adsorbed polymer materials, which enables the co-encapsulation of insulin, exenatide, and bivalirudin with a precise ratiometric control. After solidification of this adsorbed polymer layer, the release of peptides is synchronously prolonged. With the help of encapsulation, insulin achieves 8 days of glycemic control in type 1 diabetic rats with one single injection. The co-delivery of insulin and exenatide (1:1) efficiently controls the glycemic level in type 2 diabetic rats for 8 days. Weekly administration of insulin and exenatide co-encapsulated microcomposite effectively reduces the weight gain and glycosylated hemoglobin level in type 2 diabetic rats. The surface adsorption strategy sets a new paradigm to improve the pharmacokinetic and pharmacological performance of peptides, especially for the combination of peptides.

Novel glucose-responsive nanoparticles based on p-hydroxyphenethyl anisate and 3-acrylamidophenylboronic acid reduce blood glucose and ameliorate diabetic nephropathy

An insulin delivery system that self-regulates blood sugar levels, mimicking the human pancreas, can improve hyperglycaemia. At present, a glucose-responsive insulin delivery system combining AAPBA with long-acting slow release biomaterials has been developed. However, the safety of sustained-release materials and the challenges of preventing diabetic complications remain. In this study, we developed a novel polymer slow release material using a plant extract—p-hydroxyphenylethyl anisate (HPA). After block copolymerisation with AAPBA, the prepared nanoparticles had good pH sensitivity, glucose sensitivity, insulin loading rate and stability under physiological conditions and had high biocompatibility. The analysis of streptozotocin-induced diabetic nephropathy (DN) mouse model showed that the insulin-loaded injection of nanoparticles stably regulated the blood glucose levels of DN mice within 48 ​h. Importantly, with the degradation of the slow release material HPA in vivo, the renal function improved, the inflammatory response reduced, and antioxidation levels in DN mice improved. This new type of nanoparticles provides a new idea for hypoglycaemic nano-drug delivery system and may have potential in the prevention and treatment of diabetic complications.

•

We established a new glucose-responsive intelligent system with HPA.

•

p(AAPBA-b-HPA) shows good pH and glucose sensitivity.

•

p(AAPBA-b-HPA) nanoparticles can slowly release HPA and insulin.

•

This system can be used to regulate blood glucose.

•

p(AAPBA-b-HPA) nanoparticles can aid in diabetic nephropathy prevention and treatment.

Inhibiting Phase Transfer of Protein Nanoparticles by Surface Camouflage-A Versatile and Efficient Protein Encapsulation Strategy

Engineering a system with a high mass fraction of active ingredients, especially water-soluble proteins, is still an ongoing challenge. In this work, we developed a versatile surface camouflage strategy that can engineer systems with an ultrahigh mass fraction of proteins. By formulating protein molecules into nanoparticles, the demand of molecular modification was transformed into a surface camouflage of protein nanoparticles. Thanks to electrostatic attractions and van der Waals interactions, we camouflaged the surface of protein nanoparticles through the adsorption of carrier materials. The adsorption of carrier materials successfully inhibited the phase transfer of insulin, albumin, β-lactoglobulin, and ovalbumin nanoparticles. As a result, the obtained microcomposites featured with a record of protein encapsulation efficiencies near 100% and a record of protein mass fraction of 77%. After the encapsulation in microcomposites, the insulin revealed a hypoglycemic effect for at least 14 d with one single injection, while that of insulin solution was only ∼4 h.

Glucose-Sensitive Core-Cross-Linked Nanoparticles Constructed with Polyphosphoester Diblock Copolymer for Controlling Insulin Delivery

This work aims to construct biocompatible, biodegradable core-cross-linked and insulin-loaded nanoparticles which are sensitive to glucose and release insulin via cleavage of the nanoparticles in a high-concentration blood glucose environment. First, a polyphosphoester-based diblock copolymer (PBYP-g-Gluc)-b-PEEP was prepared via ring-opening copolymerization (ROP) and the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) in which PBYP and PEEP represent the polymer segments from 2-(but-3-yn-1-yloxy)-2-oxo-1,3,2-dioxaphospholane and 2-ethoxy-2-oxo-1,3,2-dioxaphospholane, respectively, and Gluc comes from 2-azidoethyl-β-d-glucopyranoside (Gluc-N3) that grafted with PBYP. The structure and molecular weight of the copolymer were characterized by 1H NMR, 31P NMR, GPC, FT-IR, and UV-vis measurements. The amphiphilic copolymer could self-assemble into core-shell uncore-cross-linked nanoparticles (UCCL NPs) in aqueous solutions and form core-cross-linked nanoparticles (CCL NPs) after adding cross-linking agent adipoylamidophenylboronic acid (AAPBA). Dynamic light scattering (DLS) and transmission electron microscopy (TEM) were used to study the self-assembly behavior of the two kinds of NPs and the effect of different Gluc group contents on the size of NPs further to verify the stability and glucose sensitivity of CCL NPs. The ability of NPs to load fluorescein isothiocyanate-labeled insulin (FITC-insulin) and their glucose-triggered release behavior were detected by a fluorescence spectrophotometer. The results of methyl thiazolyl tetrazolium (MTT) assay and hemolysis activity experiments showed that the CCL NPs had good biocompatibility. An in vivo hypoglycemic study has shown that FITC-insulin-loaded CCL NPs could reduce blood glucose and have a protective effect on hypoglycemia. This research provides a new method for constructing biodegradable and glucose-sensitive core-cross-linked nanomedicine carriers for controlled insulin release.

On-demand transdermal insulin delivery system for type 1 diabetes therapy with no hypoglycemia risks

Diabetes is a metabolic disease that is affecting an ever-increasing number of people worldwide, resulting in increased burdens on healthcare systems and societies. Constant monitoring of blood glucose levels is required to prevent serious or even deadly complications. One major challenge of diabetes management is the simple and timely administration of insulin to facilitate consistent blood glucose regulation and reduce the incidence of hypoglycemia. With this research, we construct an insulin delivery system, the delivery system is comprised of phenylboronic acid based fluorescent probes, which is used as glucose responsive linkers, mesoporous silica nanoparticles providing an insulin reservoir, and zinc oxide nanoparticles used as gate keepers. The system with glucose sensitive responsive linker exhibits controlled release of insulin under high glucose concentrations, providing prolonged blood glucose regulation and no risks of hypoglycemia. Furthermore, the system is combined with a hyaluronic-acid based microneedle patch, which exhibit efficient skin penetration for transdermal delivery. With our system, the nanoparticles provide outstanding in vivo glucose regulation when administrated by subcutaneous injection or via transdermal microneedle patch. We anticipate that our biocompatible smart glucose responsive microneedle patch (SGRM patch) will facilitate the development of clinically useful systems.

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.

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.

Copolymers containing carbohydrates and other biomolecules: design, synthesis and applications

This review highlights recent progress in random and block copolymers containing sugar and other biocompounds, including their design, synthesis, properties and selected applications.

Glucose-responsive insulin release: Analysis of mechanisms, formulations, and evaluation criteria

Diabetes mellitus has become one of the biggest medical challenges affecting millions of people globally. Alternative treatments for diabetes are currently being intensively investigated to improve the treatment efficacy and life qualities for diabetic patients. Glucose-responsive insulin release (GRIR) systems have exhibited tremendous potential to improve the normal glycemic control and to reduce the incidence of hyperglycemia and hypoglycemia, which further reduces potential complications in diabetic patients. In a given GRIR drug formulation, accuracy, response time, and reversibility of the GRIR functions are three key features enabling potential seamless control of blood glucose level. Nevertheless, there is significant challenge preventing current GRIR formulations from achieving them. This review article analyzes the most updated literature and provides insights on the impact of GRIR mechanisms, and formulations on these key features, and the relevant in vitro and in vivo evaluation methods to test these functions.

Phenylboronic acid-diol crosslinked 6-O-vinylazeloyl-d-galactose nanocarriers for insulin delivery

A new block polymer named poly 3-acrylamidophenylboronic acid-b-6-O-vinylazeloyl-d-galactose (p(AAPBA-b-OVZG)) was prepared using 3-acrylamidophenylboronic acid (AAPBA) and 6-O-vinylazeloyl-d-galactose (OVZG) via a two-step procedure involving S-1-dodecyl-S-(α', α'-dimethyl-α″-acetic acid) trithiocarbonate (DDATC) as chain transfer agent, 2,2-azobisisobutyronitrile (AIBN) as initiator and dimethyl formamide (DMF) as solvent. The structures of the polymer were examined by Fourier transform infrared spectroscopy (FT-IR) and ¹H NMR and the thermal stability was determined by thermal gravimetric analysis (TG/DTG). Transmission electron microscopy (TEM) and dynamic light scattering (DLS) were utilized to evaluate the morphology and properties of the p(AAPBA-b-OVZG) nanoparticles. The cell toxicity, animal toxicity and therapeutic efficacy were also investigated. The results indicate the p(AAPBA-b-OVZG) was successfully synthesized and had excellent thermal stability. Moreover, the p(AAPBA-b-OVZG) nanoparticles were submicron in size and glucose-sensitive in phosphate-buffered saline (PBS). In addition, insulin as a model drug had a high encapsulation efficiency and loading capacity and the release of insulin was increased at higher glucose levels. Furthermore, the nanoparticles showed a low-toxicity in cell and animal studies and they were effective at decreasing blood glucose levels of mice over 96h. These p(AAPBA-b-OVZG) nanoparticles show promise for applications in diabetes treatment using insulin or other hypoglycemic proteins.

pH-sensitive peptide hydrogel for glucose-responsive insulin delivery

Glucose-responsive system is one of important options for self-regulated insulin delivery to treat diabetes, which has become an issue of great public health concern in the world. In this study, we developed a novel and biocompatible glucose-responsive insulin delivery system using a pH-sensitive peptide hydrogel as a carrier loaded with glucose oxidase, catalase and insulin. The peptide could self-assemble into hydrogel under physiological conditions. When hypoglycemia is encountered, neighboring alkaline amino acid side chains are significantly repulsed due to reduced local pH by the enzymatic conversion of glucose into gluconic acid. This is followed by unfolding of individual hairpins, disassembly and release of insulin. The glucose-responsive hydrogel system was characterized on the basis of structure, conformation, rheology, morphology, acid-sensitivity and the amount of consistent release of insulin in vitro and vivo. The results illustrated that our system can not only regulate the blood glucose levels in vitro but also in mice models having STZ-induced diabetes.

STATEMENT OF SIGNIFICANCE

In this report, we have shown the following significance supported by the experimental results. 1. We successfully developed, characterized and screened a novel pH-responsive peptide. 2. We successfully developed a novel and biocompatible pH-sensitive peptide hydrogel as glucose-responsive insulin delivery system loaded with glucose oxidase, catalase and insulin. 3. We successfully confirmed that the hydrogel platform could regulate the blood glucose level in vitro and in vivo. Overall, we have shown enough significance and novelty with this smart hydrogel platform in terms of biomaterials, peptide chemistry, self-assembly, hydrogel and drug delivery. So we believe this manuscript is suitable for Acta Biomaterialia.

Polypeptide-participating complex nanoparticles with improved salt-tolerance as excellent candidates for intelligent insulin delivery

The strategy of introducing synthetic polypeptides with hierarchical ordered structures into glucose-responsive materials is reported in this study to achieve self-regulated release of insulin under physiological salt concentration.