Insulins today and beyond

A simple freeze-thaw based method for efficient purification of recombinant human proinsulin from inclusion bodies

Insulin is a pivotal peptide hormone essential for regulating glucose homeostasis. It has been known for over 100 years, but its production and purification methods are still under improvement. Escherichia coli based bacterial expression system is primarily used for insulin production. The human insulin protein expressed in bacteria usually forms inclusion bodies, complicating the purification process. Traditionally, insulin purification is a time-consuming process involving urea-based denaturation methods, and various refolding techniques, followed by extensive chromatographic methods. Here, we report an easy and efficient purification of human proinsulin involving freeze-thaw based solubilization method. The extracted proinsulin inclusion bodies are treated with different concentrations of urea, followed by a freeze-thaw based solubilization. The freezing was carried out at various temperatures, mainly -80 °C, -20 °C, and -196 °C to determine the optimum condition for solubilization. Highest solubilization of proinsulin from the inclusion body was achieved with 0.5M urea and -20 °C. Further Nickel NTA-based purification was performed, and the purified protein was characterized for disulfide mapping by high-resolution mass spectrometer (HRMS). We also performed glucose uptake assays to validate the functional properties of purified proinsulin. This freeze-thaw based mild solubilization approach is a fast and effective method for getting bioactive proinsulin, which will help further design better purification and processing strategies for insulin production.

Higher Order Structure Differences Among Insulin Crystalline Drugs Revealed by 2D heteronuclear NMR

During therapeutic protein development, two-dimensional (2D) heteronuclear NMR spectra can be a powerful analytical method for measuring protein higher order structure (HOS) in solution since the spectra exhibit much higher resolution than homonuclear 1H spectra. However, 2D NMR capabilities for characterizing protein HOS in crystalline states remain to be assessed, given the low 13C natural abundance and intrinsically broader lines in solid-state NMR (SSNMR). Herein, high-resolution heteronuclear correlation (HETCOR) SSNMR was utilized to directly measure intact crystal drug products of insulin human, insulin analogs of insulin lispro and insulin aspart. The fingerprint regions in 2D 1H-13C HETCOR spectra were identified, which distinguished the insulin crystals in their primary structure, HOS heterogeneity and dynamics, as well as the manufacturing processes. The HOS heterogeneity in insulin analogs is consistent with their therapeutic effect of rapid action; while insulin human crystals showed more structural homogeneity, consistent with their slower pharmacokinetics (PK) peak time than insulin analogs. Therefore, heteronuclear NMR could be broadly applicable to study protein drug dosage forms from liquid to solid, yielding improved molecular level structure data for assessing drug HOS in biosimilar drug development.

A Wearable Integrated Microneedle Electrode Patch for Exercise Management in Diabetes

Exercise is one of the preferred management strategies for diabetic patients, but the exercise mode including type, intensity, and duration time is quite different for each patient because of individual differences. Inadequate exercise has no effect on the blood glucose control, while overexercise may cause serious side effects, such as hypoglycemia and loss of blood glucose control. In this work, we report a closed-loop feedback mode for exercise management in diabetes. A minimally invasive, biocompatible microneedle electrode patch was fabricated and used for continuously monitoring the glucose in the interstitial fluid. Further, in conjunction with using a wireless electrochemical device, the glucose signals can be analyzed to output the potency of exercise and give advice on exercise management. A custom exercise given by this closed-loop feedback mode can reduce the used dose of insulin and avoid side effect during and after exercise. We believe that this work can provide a novel comprehensive guidance for diabetic patients.

Glucose-Responsive Microneedle Patch with High Insulin Loading Capacity for Prolonged Glycemic Control in Mice and Minipigs

Transdermal microneedle-mediated glucose-responsive insulin delivery systems can modulate insulin release based on fluctuations in blood glucose levels, thus maintaining normoglycemia effectively in a continuous, convenient, and minimally invasive manner. However, conventional microneedles are limited by the low drug loading capacity, making it challenging to be applied on human skin at a reasonable size for a lasting glucose-controlling effect, thus hindering their clinical translation. Here, we design a microneedle patch with a solid insulin powder core to achieve a high loading capacity of insulin (>70 wt %) as well as a glucose-sensitive polymeric shell to realize glucose-responsive insulin release. Once exposed to hyperglycemia, the formation of negatively charged glucose-boronate complexes increases the charge density of the shell matrix, leading to swelling of the shell and accelerating insulin release from the core. We have demonstrated that this glucose-responsive microneedle patch could achieve long-term regulation of blood glucose levels in both type 1 diabetic mice and minipigs (up to 48 h with patches of ∼3.5 cm2 for minipigs >25 kg).

Transplantable cell-encapsulation device using a semipermeable ethylene-vinyl alcohol copolymer membrane in a mouse diabetic model

Cell-based therapy is an attractive approach, and encapsulation of therapeutic cells is a promising strategy because it prevents immune responses and allows transplanted cells to be retrieved in case of dysfunction. Bioartificial pancreas, in which insulin-secreting cells are encapsulated in a semipermeable membrane bag, is a new class of medical device for treating type-I diabetes. In this study, we developed a macroencapsulation device in which the pancreatic beta cell line MIN6 was encapsulated in a semipermeable bag made of an ethylene-vinyl alcohol copolymer membrane. In vitro evaluation of ATP and insulin levels revealed that MIN6 cells grown in Matrigel within the device secreted insulin in response to glucose levels. Transplantation of the device lowered blood glucose levels for 30 days in diabetic mice. Histological observation revealed that MIN6 cells formed spheroids in Matrigel, and no host cells were detected within the device. Blood levels of inflammatory cytokines in the transplanted mice were similar to those in non-transplanted mice, and antibody levels in the device were lower than those in the intraperitoneal fluid. These results suggest that the semipermeable ethylene-vinyl alcohol copolymer membrane developed in this study is useful for cell encapsulation in cell-based therapies, including beta-cell macroencapsulation for type-1 diabetes.

Drug delivery using biocompatible covalent organic frameworks (COFs) towards a therapeutic approach

Covalent organic frameworks (COFs) are constructed exclusively with lightweight organic scaffolds, which can have a 2D or 3D architecture. The ease of synthesis, robust skeleton and tunable properties of COFs make them superior candidates among their counterparts for a wide range of uses including biomedical applications. In the biomedical field, drug delivery or photodynamic-photothermal (PDT-PTT) therapy can be individually considered a potential parameter to be investigated. Therefore, this comprehensive review is focused on drug delivery using COFs, highlighting the encapsulation and decapsulation of drugs by COF scaffolds and their delivery in biological media including live cells. Versatile COF scaffolds together with the delivery of several drug molecules are considered. We attempted to incorporate the status of drug encapsulation and decapsulation considering a wide range of recent publications.

Electro-responsive silk fibroin microneedles for controlled release of insulin

To date, very limited work has been done on convenient and active control of insulin release. Herein, we report an electro-responsive insulin delivery system based on thiolated silk fibroin. The disulfide cross-linking points in TSF were reduced and broken to form sulfhydryl groups under electrification, which led to the increase of microneedle swelling degree and promoted insulin release. After power failure, the sulfhydryl group is oxidised to form disulfide bond crosslinking point again, resulting in the reduction of microneedle swelling degree and thus the reduction of release rate. The insulin loaded in the electro-responsive insulin delivery system showed good reversible electroresponsive release performance. The addition of graphene reduced the microneedle resistance and increased the drug release rate under current conditions. In vivo studies on type 1 diabetic mice show that electro-responsive insulin delivery system effectively controls the blood glucose before and after feeding by switching on and off the power supply, and this blood glucose control can be maintained within the safe range (100-200 mg/dL) for a long time (11h). Such electrically responsive delivery microneedles show potential for integration with glucose signal monitoring and are expected to build closed-loop insulin delivery systems.

Distinct Roles for Brain and Pancreas in Basal and Postprandial Glucose Homeostasis

The glucose homeostasis system ensures that the circulating glucose level is maintained within narrow physiological limits both in the fasting (or basal) state and following a nutrient challenge. Although glucose homeostasis is traditionally conceptualized as a single overarching system, evidence reviewed here suggests that basal glycemia and glucose tolerance are governed by distinct control systems. Specifically, whereas glucose tolerance appears to be determined largely by interactions between insulin secretion and insulin sensitivity, basal-state glucose homeostasis is predominated by insulin-independent mechanisms governed largely by the brain. In addition to a new perspective on how glucose homeostasis is achieved, this "dual control system" hypothesis offers a feasible and testable explanation for observations that are otherwise difficult to reconcile and sheds new light on the integration of central and peripheral metabolic control mechanisms. The implications of this model for the pathogenesis and treatment of impaired fasting glucose, impaired glucose tolerance, and type 2 diabetes are also discussed.

Polymer-Based Nanostructures for Pancreatic Beta-Cell Imaging and Non-Invasive Treatment of Diabetes

Diabetes poses major economic, social, and public health challenges in all countries worldwide. Besides cardiovascular disease and microangiopathy, diabetes is a leading cause of foot ulcers and lower limb amputations. With the continued rise of diabetes prevalence, it is expected that the future burden of diabetes complications, early mortality, and disabilities will increase. The diabetes epidemic is partly caused by the current lack of clinical imaging diagnostic tools, the timely monitoring of insulin secretion and insulin-expressing cell mass (beta (β)-cells), and the lack of patients' adherence to treatment, because some drugs are not tolerated or invasively administrated. In addition to this, there is a lack of efficient topical treatment capable of stopping the progression of disabilities, in particular for treating foot ulcers. In this context, polymer-based nanostructures garnered significant interest due to their tunable physicochemical characteristics, rich diversity, and biocompatibility. This review article emphasizes the last advances and discusses the prospects in the use of polymeric materials as nanocarriers for β-cell imaging and non-invasive drug delivery of insulin and antidiabetic drugs in the management of blood glucose and foot ulcers.

Stimuli-Responsive Boron-Based Materials in Drug Delivery

Drug delivery systems, which use components at the nanoscale level as diagnostic tools or to release therapeutic drugs to particular target areas in a regulated manner, are a fast-evolving field of science. The active pharmaceutical substance can be released via the drug delivery system to produce the desired therapeutic effect. The poor bioavailability and irregular plasma drug levels of conventional drug delivery systems (tablets, capsules, syrups, etc.) prevent them from achieving sustained delivery. The entire therapy process may be ineffective without a reliable delivery system. To achieve optimal safety and effectiveness, the drug must also be administered at a precision-controlled rate and the targeted spot. The issues with traditional drug delivery are overcome by the development of stimuli-responsive controlled drug release. Over the past decades, regulated drug delivery has evolved considerably, progressing from large- and nanoscale to smart-controlled drug delivery for several diseases. The current review provides an updated overview of recent developments in the field of stimuli-responsive boron-based materials in drug delivery for various diseases. Boron-containing compounds such as boron nitride, boronic acid, and boron dipyrromethene have been developed as a moving field of research in drug delivery. Due to their ability to achieve precise control over drug release through the response to particular stimuli (pH, light, glutathione, glucose or temperature), stimuli-responsive nanoscale drug delivery systems are attracting a lot of attention. The potential of developing their capabilities to a wide range of nanoscale systems, such as nanoparticles, nanosheets/nanospheres, nanotubes, nanocarriers, microneedles, nanocapsules, hydrogel, nanoassembly, etc., is also addressed and examined. This review also provides overall design principles to include stimuli-responsive boron nanomaterial-based drug delivery systems, which might inspire new concepts and applications.

Nonmetallic N/C Nanozyme Performs Continuous Consumption of Glu for Inhibition of Colorectal Cancer Cells

Colorectal cancer (CRC) is the third leading cause of cancer-related mortality. 5-Fluorouracil (5-FU) is the first choice for treatment of CRC, but it cannot avoid the negative effects from local high glucose (Glu) in tumor. Recently, 5-FU therapy has been combined with other treatment modalities for CRC synergistic therapy. Although these combination therapy strategies are more effective in cancer therapy, the toxicity side effects to the liver and cause metabolic acidosis still exist. Herein, we report an emerging amorphous honeycomb-like nitrogen-doped carbon (N/C) nanozyme with nicotinamide adenine dinucleotide (NADH) oxidase and catalase (CAT) activity and cascade it with natural glucose dehydrogenase (GDH) to realize NAD⁺ regeneration and further hyperglycemia management. In this case, by the coupling of N/C nanozyme with natural GDH to form a N/C-GDH system, the electron transfer route can switch from Glu to a common but limited electron receptor, i.e., NAD⁺ to ubiquitous large amounts of oxygen, achieving the purpose of sustainable consumption of Glu under NAD⁺ circulation and regeneration, and importantly escaping the generation of toxic H₂O₂. The combination of the N/C-GDH system and 5-FU on CRC cells was investigated to assess their synergistic bioeffects. Notably, our results showed that the N/C-GDH system and 5-FU in combination significantly suppress the proliferation of human colon cancer cells (HCT-116) by reducing the sugar level and induced apoptosis compared with either material or drug used alone. This work expands the nanozymes in blood Glu management as well as the promising cancer cell inhibition and provides the possibility of nonmetallic nanomaterials in the realization of effective treatment of cancer.

Carbon Dots Embedded Hybrid Microgel with Phenylboronic Acid as Monomer for Fluorescent Glucose Sensing and Glucose-Triggered Insulin Release at Physiological pH

A multifunctional and biocompatible hybrid microgel (poly(VPBA-AAm)-CD) using N, S-doped carbon dots (CDs) and ethylene glycol dimethacrylate (EGDMA) as cross-linking agents, and 4-vinylbenzene boronic acid (VPBA) and acrylamide (AAm) as monomers, was designed in this work. This microgel can be easily prepared by a simple one-pot radical dispersion polymerization of the reactants using a rationally designed hydrogen-bonded complex method. The hybrid microgels were spherical particles with a smooth surface and an average particle size of 234 ± 8 nm. The poly(VPBA-AAm)-CD microgel displayed the glucose-responsive swelling within a clinically concerned range at a physiological pH and could realize the controllable release of insulin. In addition, the release rate of insulin in the hybrid microgel (poly(VPBA-AAm)-CD) could be triggered by glucose concentrations in the solution, and the increasing glucose concentrations can accelerate the insulin release. Further in vitro cytotoxicity studies showed that the microgel had good biocompatibility and no obvious toxicity to the cells. These indicate that the prepared microgel (poly(VPBA-AAm)-CD) may supply a new pattern for the self-regulating therapy of insulin deficiency in diabetes.

Stimuli-Responsive Microneedles as a Transdermal Drug Delivery System: A Demand-Supply Strategy

Microneedles are one of the most prominent approaches capable of physically disrupting the stratum corneum without devastating the deeper tissues to deliver both small molecules and macromolecules into the viable epidermis/dermis for local/systemic effects. Over the past two decades, microneedles have caught the attention of many researchers because of their outstanding advantages over oral and parenteral drug delivery systems such as self-administration, pain-free, steady-plasma concentration maintenance, avoidance of first-pass hepatic biotransformation, and so on. So far, scientists have reported various types of microneedle patches to deliver the loaded therapeutics as soon as the microneedles are inserted into the skin, regardless of the demand for therapeutics to treat a specific condition. This way of drug delivery can lead to potential risks such as poor therapeutic efficacy or drug overdose. The stimuli-responsive microneedles are the most predominant tool to achieve the on-demand/need-based drug delivery, leading to safe and effective treatment. Various natural and synthetic polymers that can undergo significant transitions such as swelling, shrinking, dissolution, or disintegration play a pivotal role in the development of stimuli-responsive microneedles. The current Review provides brief information about the history, emergence, type, and working principles of microneedles. Furthermore, it selectively discusses various exogenous and endogenous stimuli-responsive microneedles along with their mechanism of action involved in treating different disease conditions. Collaterally, the emergence of "closed-loop" combinatorial stimuli-responsive microneedle patches for precise delivery of therapeutics is meticulously canvassed. Subsequently, it covers the patents of different stimuli-responsive microneedles and further highlights the existing challenges and future perspectives concerning clinical application and large-scale production.

Insulin Centennial: Milestones influencing the development of insulin preparations since 1922

During 1921 to 1922, a team effort by Banting, Macleod, Collip and Best isolated and purified insulin and demonstrated its life-giving properties, giving rise to the birth of insulin therapy. In the early years (1922-1950), priorities revolved around the manufacture of insulin to meet demand, improving purity to avoid allergic reactions, establishing insulin standards and increasing its duration of action to avoid multiple daily injections. Shortly after the emergence of insulin, Joslin and Allen advocated the need to achieve and maintain good glycaemic control to realize its full potential. Although this view was opposed by some during a dark period in the history of insulin, it was subsequently endorsed some 60 years later endorsed by the Diabetes Control and Complications Trial and United Kingdom Prospective Diabetes Study. Major scientific advances by the Nobel Laureates Sanger, Hodgkin, Yalow and Gilbert and also by Steiner have revolutionized the understanding of diabetes and facilitated major advances in insulin therapy. The more recent advent of recombinant technology over the last 40 years has provided the potential for unlimited source of insulin, and the ability to generate various insulin 'analogues', in an attempt to better replicate normal insulin secretory patterns. The emerging biosimilars now provide the opportunity to improve availability at a lower cost.

The ongoing evolution of basal insulin therapy over 100 years and its promise for the future

The evolution of basal insulin therapy over the past 100 years since the discovery of insulin is a testimony to the biomedical bench-to-bedside process, wherein incremental advances in the basic sciences are progressively translated over time into a series of enhancements in clinical care, each building upon the success of its predecessors. The emergence of recombinant DNA technology and the resultant biosynthesis of human insulin in the 1980s provided the critical capacity to bioengineer designer insulin analogues with pharmacokinetic and pharmacodynamic properties that can better mimic, although not fully replicate, the effects of endogenous insulin secretion. Through these efforts, basal insulin therapy has progressed over this time from first-generation analogues (glargine U-100, detemir) to second-generation analogues (glargine U-300, degludec) to ultra-long-acting formulations that are suitable for administration once weekly (icodec). Each iteration in this progression has represented a step closer towards the goal of replicating the continuous secretion of insulin that normally comprises the basal output of the pancreatic beta-cells between meals, during episodes of fasting and overnight. However, it may be that we may have reached the achievable limit in the context of an "open-loop" approach, such that only with the addition of closed loop control will we be able to achieve physiologic basal insulin replacement. In this review, we will examine the evolution of basal insulin therapy over the past 100 years and its implications for patient care and outcomes in current practice and the future.

Polymeric microneedle-mediated sustained release systems: Design strategies and promising applications for drug delivery

Parenteral sustained release drug formulations, acting as preferable platforms for long-term exposure therapy, have been wildly used in clinical practice. However, most of these delivery systems must be given by hypodermic injection. Therefore, issues including needle-phobic, needle-stick injuries and inappropriate reuse of needles would hamper the further applications of these delivery platforms. Microneedles (MNs) as a potential alternative system for hypodermic needles can benefit from minimally invasive and self-administration. Recently, polymeric microneedle-mediated sustained release systems (MN@SRS) have opened up a new way for treatment of many diseases. Here, we reviewed the recent researches in MN@SRS for transdermal delivery, and summed up its typical design strategies and applications in various diseases therapy, particularly focusing on the applications in contraception, infection, cancer, diabetes, and subcutaneous disease. An overview of the present clinical translation difficulties and future outlook of MN@SRS was also provided.

Insulin Granule-Loaded MicroPlates for Modulating Blood Glucose Levels in Type-1 Diabetes

Type-1 diabetes (T1DM) is a chronic metabolic disorder resulting from the autoimmune destruction of β cells. The current standard of care requires multiple, daily injections of insulin and accurate monitoring of blood glucose levels (BGLs); in some cases, this results in diminished patient compliance and increased risk of hypoglycemia. Herein, we engineered hierarchically structured particles comprising a poly(lactic-co-glycolic) acid (PLGA) prismatic matrix, with a 20 × 20 μm base, encapsulating 200 nm insulin granules. Five configurations of these insulin-microPlates (INS-μPLs) were realized with different heights (5, 10, and 20 μm) and PLGA contents (10, 40, and, 60 mg). After detailed physicochemical and biopharmacological characterizations, the tissue-compliant 10H INS-μPL, realized with 10 mg of PLGA, presented the most effective release profile with ∼50% of the loaded insulin delivered at 4 weeks. In diabetic mice, a single 10H INS-μPL intraperitoneal deposition reduced BGLs to that of healthy mice within 1 h post-implantation (167.4 ± 49.0 vs 140.0 ± 9.2 mg/dL, respectively) and supported normoglycemic conditions for about 2 weeks. Furthermore, following the glucose challenge, diabetic mice implanted with 10H INS-μPL successfully regained glycemic control with a significant reduction in AUC_0-120min (799.9 ± 134.83 vs 2234.60 ± 82.72 mg/dL) and increased insulin levels at 7 days post-implantation (1.14 ± 0.11 vs 0.38 ± 0.02 ng/mL), as compared to untreated diabetic mice. Collectively, these results demonstrate that INS-μPLs are a promising platform for the treatment of T1DM to be further optimized with the integration of smart glucose sensors.

Advances of microneedles in hormone delivery

The skin is recognized as a potential target for local and systemic drug delivery and hormone. However, the transdermal route of drug administration seems to be limited by substantial barrier properties of the skin. Recently, delivering hormone via the skin by transdermal patches is a big challenge because of the presence of the stratum corneum that prevents the application of hormone via this route. In order to overcome the limitations, microneedle (MN), consisting of micro-sized needles, are a promising approach to drill the stratum corneum and release hormone into the dermis via a minimal-invasive route. This review aimed to highlight advances in research on the development of MNs-based therapeutics for their implications in hormone delivery. The challenges during clinical translation of MNs from bench to bedside are also discussed.

Improved oral delivery of insulin by PLGA nanoparticles coated with 5β-cholanic acid conjugated glycol chitosan

Oral insulin has been regarded as the best alternative to insulin injection in therapy of diabetes because of its convenience and painlessness. However, several obstacles in the gastrointestinal tract, such as gastric acid and enzyme, greatly reduce the bioavailability of oral insulin. Herein, we report design and preparation of poly (d, l-lactic-co-glycolic acid) nanoparticles (PLGA NPs) coated with 5β-cholanic acid modified glycol chitosan (GC-CA) (GC-CA@PLGA NPs) to improve the oral delivery of insulin. The GC-CA@PLGA NPs with the size of (302.73 ± 5.13 nm) and zeta potential of (25.03 ± 0.31 mV) were synthesized using the double-emulsion method. The insulin-loading capacity and encapsulation efficiency were determined to be 5.77 ± 0.58% and 51.99 ± 5.27%, respectively. Compared with GC-modified PLGA NPs (GC@PLGA NPs) and bare PLGA NPs, the GC-CA@PLGA NPs showed excellent stability and uptake by Caco-2 cells after simulated gastric acid digestion. Further experiment suggests good biocompatibility of GC-CA@PLGA NPs, including hemolysis and cytotoxicity. Inin vivoexperiment, the insulin loaded in the GC-CA@PLGA NPs exhibited a long-term and stable release profile for lowering blood glucose and presented 30.43% bioavailability in oral administration. In brief, we have developed an efficient and safe drug delivery system, GC-CA@PLGA NPs, for significantly improved oral administration of insulin, which may find potential application in the treatment of diabetes.

Structural principles of insulin formulation and analog design: A century of innovation

BACKGROUND

The discovery of insulin in 1921 and its near-immediate clinical use initiated a century of innovation. Advances extended across a broad front, from the stabilization of animal insulin formulations to the frontiers of synthetic peptide chemistry, and in turn, from the advent of recombinant DNA manufacturing to structure-based protein analog design. In each case, a creative interplay was observed between pharmaceutical applications and then-emerging principles of protein science; indeed, translational objectives contributed to a growing molecular understanding of protein structure, aggregation and misfolding.

SCOPE OF REVIEW

Pioneering crystallographic analyses-beginning with Hodgkin's solving of the 2-Zn insulin hexamer-elucidated general features of protein self-assembly, including zinc coordination and the allosteric transmission of conformational change. Crystallization of insulin was exploited both as a step in manufacturing and as a means of obtaining protracted action. Forty years ago, the confluence of recombinant human insulin with techniques for site-directed mutagenesis initiated the present era of insulin analogs. Variant or modified insulins were developed that exhibit improved prandial or basal pharmacokinetic (PK) properties. Encouraged by clinical trials demonstrating the long-term importance of glycemic control, regimens based on such analogs sought to resemble daily patterns of endogenous β-cell secretion more closely, ideally with reduced risk of hypoglycemia.

MAJOR CONCLUSIONS

Next-generation insulin analog design seeks to explore new frontiers, including glucose-responsive insulins, organ-selective analogs and biased agonists tailored to address yet-unmet clinical needs. In the coming decade, we envision ever more powerful scientific synergies at the interface of structural biology, molecular physiology and therapeutics.

Recent advances in microneedles-mediated transdermal delivery of protein and peptide drugs

Proteins and peptides have become a significant therapeutic modality for various diseases because of their high potency and specificity. However, the inherent properties of these drugs, such as large molecular weight, poor stability, and conformational flexibility, make them difficult to be formulated and delivered. Injection is the primary route for clinical administration of protein and peptide drugs, which usually leads to poor patient's compliance. As a portable, minimally invasive device, microneedles (MNs) can overcome the skin barrier and generate reversible microchannels for effective macromolecule permeation. In this review, we highlighted the recent advances in MNs-mediated transdermal delivery of protein and peptide drugs. Emphasis was given to the latest development in representative MNs design and fabrication. We also summarize the current application status of MNs-mediated transdermal protein and peptide delivery, especially in the field of infectious disease, diabetes, cancer, and other disease therapy. Finally, the current status of clinical translation and a perspective on future development are also provided.

A Fully Integrated Closed-Loop System Based on Mesoporous Microneedles-Iontophoresis for Diabetes Treatment

A closed-loop system that can mini-invasively track blood glucose and intelligently treat diabetes is in great demand for modern medicine, yet it remains challenging to realize. Microneedles technologies have recently emerged as powerful tools for transdermal applications with inherent painlessness and biosafety. In this work, for the first time to the authors' knowledge, a fully integrated wearable closed-loop system (IWCS) based on mini-invasive microneedle platform is developed for in situ diabetic sensing and treatment. The IWCS consists of three connected modules: 1) a mesoporous microneedle-reverse iontophoretic glucose sensor; 2) a flexible printed circuit board as integrated and control; and 3) a microneedle-iontophoretic insulin delivery component. As the key component, mesoporous microneedles enable the painless penetration of stratum corneum, implementing subcutaneous substance exchange. The coupling with iontophoresis significantly enhances glucose extraction and insulin delivery and enables electrical control. This IWCS is demonstrated to accurately monitor glucose fluctuations, and responsively deliver insulin to regulate hyperglycemia in diabetic rat model. The painless microneedles and wearable design endows this IWCS as a highly promising platform to improve the therapies of diabetic patients.

A boronate gel-based synthetic platform for closed-loop insulin delivery systems

Diabetes is one of the most devastating global diseases with an ever-increasing number of patients. Achieving persistent glycemic control in a painless and convenient way is an unmet goal for diabetes management. Insulin therapy is commonly utilized for diabetes treatment and usually relies on patient self-injection. This not only impairs a patient’s quality of life and fails to precisely control the blood glucose level but also brings the risk of life-threatening hypoglycemia. “closed-loop” insulin delivery systems could avoid these issues by providing on-demand insulin delivery. However, safety concerns limit the application of currently developed electronics-derived or enzyme-based systems. Phenylboronic acid (PBA), with the ability to reversibly bind glucose and a chemically tailored binding specificity, has attracted substantial attention in recent years. This focus review provides an overview of PBA-based versatile insulin delivery platforms developed in our group, including new PBA derivatives, glucose-responsive gels, and gel-combined medical devices, with a unique “skin layer” controlled diffusion feature.

Prion-derived tetrapeptide stabilizes thermolabile insulin via conformational trapping

Unfolding followed by fibrillation of insulin even in the presence of various excipients grappled with restricted clinical application. Thus, there is an unmet need for better thermostable, nontoxic molecules to preserve bioactive insulin under varying physiochemical perturbations. In search of cross-amyloid inhibitors, prion-derived tetrapeptide library screening reveals a consensus V(X)YR motif for potential inhibition of insulin fibrillation. A tetrapeptide VYYR, isosequential to the β2-strand of prion, effectively suppresses heat- and storage-induced insulin fibrillation and maintains insulin in a thermostable bioactive form conferring adequate glycemic control in mouse models of diabetes and impedes insulin amyloidoma formation. Besides elucidating the critical insulin-IS1 interaction (R4 of IS1 to the N24 insulin B-chain) by nuclear magnetic resonance spectroscopy, we further demonstrated non-canonical dimer-mediated conformational trapping mechanism for insulin stabilization. In this study, structural characterization and preclinical validation introduce a class of tetrapeptide toward developing thermostable therapeutically relevant insulin formulations.

Erythrocyte-Membrane-Enveloped Biomineralized Metal-Organic Framework Nanoparticles Enable Intravenous Glucose-Responsive Insulin Delivery

A "closed-loop" insulin delivery system that can mimic the dynamic and glucose-responsive insulin secretion as islet β-cells is desirable for the therapy of type 1 and advanced type 2 diabetes mellitus (T1DM and T2DM). Herein, we introduced a kind of "core-shell"-structured glucose-responsive nanoplatform to achieve intravenous "smart" insulin delivery. A finely controlled one-pot biomimetic mineralization method was utilized to coencapsulate insulin, glucose oxidase (GOx), and catalase (CAT) into the ZIF-8 nanoparticles (NPs) to construct the "inner core", where an efficient enzyme cascade system (GOx/CAT group) served as an optimized glucose-responsive module that could rapidly catalyze glucose to yield gluconic acid to lower the local pH and effectively consume the harmful byproduct hydrogen peroxide (H₂O₂), inducing the collapse of pH-sensitive ZIF-8 NPs to release insulin. The erythrocyte membrane, a sort of natural biological derived lipid bilayer membrane which has intrinsic biocompatibility, was enveloped onto the surface of the "inner core" as the "outer shell" to protect them from elimination by the immune system, thus making the NPs intravenously injectable and could stably maintain a long-term existence in blood circulation. The in vitro and in vivo results indicate that our well-designed nanoplatform possesses an excellent glucose-responsive property and can maintain the blood glucose levels of the streptozocin (STZ)-induced type 1 diabetic mice at the normoglycemic state for up to 24 h after being intravenously administrated, confirming an intravenous insulin delivery strategy to overcome the deficits of conventional daily multiple subcutaneous insulin administration and offering a potential candidate for long-term T1DM treatment.

Insulin and insulin analogs as antidiabetic therapy: A perspective from clinical trials

The discovery of insulin in 1921 and the progress achieved in the ensuing century highlight the promise and challenge of biochemically modifying the molecule to achieve optimization of its delivery and therapeutic efficacy. Normal endogenous insulin secretion consists of a highly orchestrated physiologic loop wherein multiple metabolic signals trigger the pancreatic β cells to secrete the precise amount of insulin into the portal system required to maintain euglycemia. Accordingly, in the treatment of diabetes, attempting to replicate this complex physiology with exogenous insulin therapy given subcutaneously presents a clinical challenge. In this context, recombinant DNA-based technology has enabled the development of insulin analogs that have been specifically designed to confer advantageous pharmacodynamic features that can better mimic endogenous insulin secretion. In this review, we discuss the development of the most widely available insulin preparations and provide evidence-based insight into their use in clinical practice.

In vivo oral insulin delivery via covalent organic frameworks

With diabetes being the 7th leading cause of death worldwide, overcoming issues limiting the oral administration of insulin is of global significance. The development of imine-linked-covalent organic framework (nCOF) nanoparticles for oral insulin delivery to overcome these delivery barriers is herein reported. A gastro-resistant nCOF was prepared from layered nanosheets with insulin loaded between the nanosheet layers. The insulin-loaded nCOF exhibited insulin protection in digestive fluids in vitro as well as glucose-responsive release, and this hyperglycemia-induced release was confirmed in vivo in diabetic rats without noticeable toxic effects. This is strong evidence that nCOF-based oral insulin delivery systems could replace traditional subcutaneous injections easing insulin therapy.

Study on the Influencing Factors of Hypoglycemic Effect of Folate Targeted Polymersomes Encapsulating Insulin

PURPOSE

To study the effects of the density of folic acid (FA) on the hypoglycemic ability of FA-targeted polymersomes as oral insulin carriers. Also to study the change of the hypoglycemic effect of FA-targeted mixed polymersomes added with various mass ratio of d-α-tocopherol polyethylene glycol 1000 succinate (TPGS).

METHODS

The FA-targeted polymersomes with different FA molar contents were prepared. The in vitro insulin release experiments in different media for FA-targeted polymersomes with various FA contents were studied. Their quantitative cellular uptake in Caco-2 cells was examined. The in vivo hypoglycemic activity of FA-targeted polymersomes was also studied with diabetic rats. The polymersomes with the optimal FA molar content was chosen to prepare mixed polymersomes with various TPGS contents.

RESULTS

Among insulin-loaded FA-targeted polymersomes with four different FA molar contents, insulin-loaded polymersomes with 10% FA molar content (insulin-loaded 10%FA-Ps) showed the hightest cellular uptake and the best hypoglycemic response. In addition, the insulin-loaded FA-Ps/TPGS5:1 mixed polymersomes exhibited higher cellular uptake and better hypoglycemic response than the other two insulin-loaded mixed polymersomes adding TPGS did.

CONCLUSIONS

FA-Ps/TPGS5:1 could be a promising formulation for the oral administration of insulin.

Nano-encapsulated Tinospora cordifolia (Willd.) using poly (D, L-lactide) nanoparticles educe effective control in streptozotocin-induced type 2 diabetic rats

The therapeutics for type 2 diabetes mellitus has emerged in the current century towards nanomedicine incorporated with plant active compounds. In this study, Tinospora cordifolia loaded poly (D, L-lactide) (PLA) nanoparticles (NPs) were evaluated in vivo for their anti-hyperglycemic potency towards streptozotocin-induced type 2 diabetic rats. T. cordifolia loaded PLA NPs were synthesised by the double solvent evaporation method using PLA polymer. The NPs were then characterised and administrated orally for 28 successive days to streptozotocin-induced diabetic rats. The PLA NPs had significant anti-diabetic effects which were equal to the existing anti-diabetic drug glibenclamide. The antidiabetic activity is due to the synergism of compounds present in stem extract of the plant which reduced the side effects and anti-diabetic.

Biphasic human insulin 30 thrice daily, is it reasonable?

Objective

To evaluate the efficacy and safety of thrice daily Biphasic Human Insulin 30 (BHI 30) versus the traditional twice-daily regimen in type 2 diabetes mellitus (T2DM) patients. It’s a cross over single clinical study. Twenty-two diabetic patients who were already using BHI 30 in twice or thrice daily regimens with or without metformin were included. At the 1st interval; patients continued on their usual insulin regimen as twice or thrice daily injections with adjustment of insulin doses guided by their glucose readings. On the 2nd interval; patients were switched to the other regimen with the same total daily insulin dose redistributed.

Results

There was a significant decrease in HbA1c level (p < 0.05) at the end of the first 3 months of trial regardless on which regimen the patient started, but there was no significant difference in the mean HbA1c reduction in patients when they were on twice daily insulin injections (1.1 ± 1.3) versus the time they were on thrice daily insulin injections (0.8 ± 1.71), p > 0.05. On the other hand, patients had lower average blood glucose readings (mg/dl) when they were on thrice daily insulin injections (161.4 ± 62.7) compared to twice daily regimen (166.0 ± 69.5), p < 0.05.

Microgel encapsulated nanoparticles for glucose-responsive insulin delivery

An insulin delivery system that self-regulates blood glucose levels has the potential to limit hypoglycemic events and improve glycemic control. Glucose-responsive insulin delivery systems have been developed by coupling glucose oxidase with a stimuli-responsive biomaterial. However, the challenge of achieving desirable release kinetics (i.e., insulin release within minutes after glucose elevation and duration of release on the order of weeks) still remains. Here, we develop a glucose-responsive delivery system using encapsulated glucose-responsive, acetalated-dextran nanoparticles in porous alginate microgels. The nanoparticles respond rapidly to changes in glucose concentrations while the microgels provide them with protection and stability, allowing for extended glucose-responsive insulin release. This system reduces blood sugar in a diabetic mouse model at a rate similar to naked insulin and responds to a glucose challenge 3 days after administration similarly to a healthy animal. With 2 doses of microgels containing 60 IU/kg insulin each, we are able to achieve extended glycemic control in diabetic mice for 22 days.

Nanoparticles-encapsulated polymeric microneedles for transdermal drug delivery

Polymeric microneedles (MNs) have been leveraged as a novel transdermal drug delivery platform for effective drug permeation, which were widely used in the treatment of various diseases. However, issues including limited loading capacity of hydrophobic drugs, uncontrollable drug release rates, and monotonic therapeutic strategy hamper the further application of polymeric MNs. As a recent emerging research topic, drawing inspiration from the ways that nanomedicine integrated with MNs have opened new avenues for disease therapy. In this review, we examined the recent studies employing nanoparticles (NPs)-encapsulated polymeric MNs (NPs@MNs) for transdermal delivery of various therapeutic cargos, particularly focused on the application of NPs@MNs for diabetes therapy, infectious disease therapy, cancer therapy, and other dermatological disease therapy. We also provided an overview of the clinical potential and future translation of NPs@MNs.

Polymer-Covalent Organic Frameworks Composites for Glucose and pH Dual-Responsive Insulin Delivery in Mice

Glucose and pH dual-responsive insulin delivery carriers that have been validated in animal models, remain elusive and much desired. Herein, a new class of covalent organic frameworks (COFs)-based insulin delivery nanocarriers is developed by encapsulating insulin (Ins) and glucose oxidase (GOx) into COFs (COF-1 and COF-5) via both Brønsted and Lewis type (N:→B) complexations. Subsequently, polyethylene glycolated fluorescein isothiocyanate (FITC-PEG) is incorporated into the COFs via the exchange reactions between the disulfide in insulin chains and the thiol in FITC-PEG to afford a robust nano-assembly (FITC-PEG-COF@Ins-GOx). In vitro, the nanocarriers rely on the boroxine-linked COFs' response to pH and glucose dual-stimulation and rendered sustainable insulin delivery. In vivo, the polymer-COFs composite displays excellent long-acting anti-diabetic effects on type 1 diabetic mice within 72 h without side effects after one injection. More intriguingly, the nanocomposites also show great promise for the efficient delivery of native proteins with high generality. To the authors' knowledge, this represents the first study pertaining to a facile methodology to prepare COF-based insulin-delivery nanocarriers for in vitro and in vivo therapeutic applications.

Smart Microneedles with Porous Polymer Layer for Glucose-Responsive Insulin Delivery

A closed-loop system imitating the function of pancreatic cells, connected to microneedles (MNs) that automatically "release" insulin in response to the blood glucose (BG) levels would be highly satisfactory for improving the quality of life and health for diabetes patients. This paper describes an easy, fast and simple technique of coating a porous polymer layer on stainless steel (SS) MNs that release insulin in a glucose-responsive fashion. It was fabricated by sealing insulin, sodium bicarbonate (a pH-sensitive element [NaHCOз]) and glucose oxidase (glucose-specific enzymes [GOx]) into the pores of a porous polymer coating. Glucose can passively diffuse into the pores and become oxidized to gluconic acid by GOx, thereby causing a decrease in local pH. The subsequent reaction of protons with NaHCOз forms carbon dioxide (CO2) which creates pressure inside the pores, thereby rupturing the thin polymer film and releasing the encapsulated insulin. Field emission scanning electron microscopy (FE-SEM) images displayed that upon the exposure of MNs to glucose-free phosphate buffer saline (PBS) with pH 7.4, the pores of the porous MNs were closed, while in MNs exposed to a hyperglycemic glucose level, the pores were opened and the thin film burst. These MNs demonstrated both in vitro (in porcine skin and PBS) and in vivo (in diabetic rats) glucose-mediated insulin release under hyperglycemic conditions with rapid responsiveness. This study validated that the release of insulin from porous MNs was effectively correlated with glucose concentration.

Injectable Silk Fibroin-Based Hydrogel for Sustained Insulin Delivery in Diabetic Rats

Diabetes is a chronic disease affecting over 400 million people worldwide. Inadequate production of insulin due to loss of beta cells or insulin resistance within the body imbalances the glucose homeostasis, resulting in an abrupt increase of blood glucose level. The conventional and last resort of treatment involves repeated subcutaneous insulin injections to maintain the physiological glucose homeostasis. However, continuous and multiple subcutaneous injections are associated with poor patient compliance and local amyloidosis of insulin, which can be overcome with controlled and sustained insulin delivery. In this context, we have designed and formulated an injectable silk fibroin hydrogel (iSFH) to realize sustained insulin delivery over a prolonged period under diabetic conditions. The specific composition of glycol additives (ethylene glycol and triethylene glycol) allowed the silk fibroin protein to form an injectable hydrogel within 50 min. The detailed characterization of iSFH by a field-emission scanning electron microscope displayed the desired mesoporous structures, which are appropriate for drug (insulin) encapsulation in its active form. Interestingly, the subcutaneous injection of iSFH-encapsulated insulin (insulin-iSFH) in diabetic T1DM Wistar rats showed controlled release of insulin and restored physiological glucose homeostasis up to 4 days. The biocompatible and biodegradable nature of iSFH makes it a potential drug delivery system for active storage, and controlled and sustained delivery of insulin in diabetic conditions to maintain the physiological glucose level.

Glucose-responsive insulin patch for the regulation of blood glucose in mice and minipigs

Glucose-responsive insulin delivery systems that mimic pancreatic endocrine function could enhance health and improve quality of life for people with type 1 and type 2 diabetes with reduced β-cell function. However, insulin delivery systems with rapid in vivo glucose-responsive behaviour typically have limited insulin-loading capacities and cannot be manufactured easily. Here, we show that a single removable transdermal patch, bearing microneedles loaded with insulin and a non-degradable glucose-responsive polymeric matrix, and fabricated via in situ photopolymerization, regulated blood glucose in insulin-deficient diabetic mice and minipigs (for minipigs >25 kg, glucose regulation lasted >20 h with patches of ~5 cm2). Under hyperglycaemic conditions, phenylboronic acid units within the polymeric matrix reversibly form glucose-boronate complexes that-owing to their increased negative charge-induce the swelling of the polymeric matrix and weaken the electrostatic interactions between the negatively charged insulin and polymers, promoting the rapid release of insulin. This proof-of-concept demonstration may aid the development of other translational stimuli-responsive microneedle patches for drug delivery.

Composition-Engineered Metal-Organic Framework-Based Microneedles for Glucose-Mediated Transdermal Insulin Delivery

Elaborately designed glucose-responsive insulin-delivery systems are highly desirable for the treatment of diabetes because it can secrete insulin depending on blood glucose levels. Herein, mimic multi-enzyme metal-organic framework (MOF)-based (insulin and glucose oxidase-loaded cobalt-doped ZIF-8, abbreviated as Ins/GOx@Co-ZIF-8) stimuli-responsive microneedles (MNs) were designed for painless glucose-mediated transdermal administration. In this work, GOx and Co²⁺ ions were engineered into MOFs to construct a mimic multi-enzyme vehicle. GOx in the MOF, as the glucose-responsive factor, could catalyze glucose into gluconic acid with the formation of H₂O₂ as the byproduct. The gluconic acid formed decreases the local pH in MOFs, resulting in the degradation of MOFs and thus preloaded insulin would be released. Meanwhile, catalyzed by Co²⁺ ions in the MOF, the byproduct H₂O₂ was decomposed. Possible free Co²⁺ ions would be chelated by EDTA-SiO₂ nanoparticles in MNs and removed by peeling MNs off. The as-obtained mimic multi-enzyme MOF-based MNs showed good dependence on glucose concentration without divulging H₂O₂ and Co²⁺ ions and enough stiffness to penetrate into skin. This study offers a new strategy, using facilely synthesized MOFs as depots to integrate with MNs, for designing stimuli-responsive transdermal drug-delivery systems.

Functional zwitterionic biomaterials for administration of insulin

This review summarizes the structures and biomedical applications of zwitterionic biomaterials in the administration of insulin.

Smartphone-powered iontophoresis-microneedle array patch for controlled transdermal delivery

The incidence rate of diabetes has been increasing every year in nearly all nations and regions. The traditional control of diabetes using transdermal insulin delivery by metal needles is generally associated with pain and potential infections. While microneedle arrays (MAs) have emerged as painless delivery techniques, the integration of MA systems with electronic devices to precisely control drug delivery has rarely been realized. In this study, we developed an iontophoresis-microneedle array patch (IMAP) powered by a portable smartphone for the active and controllable transdermal delivery of insulin. The IMAP in situ integrates iontophoresis and charged nanovesicles into one patch, achieving a one-step drug administration strategy of "penetration, diffusion and iontophoresis". The MA of the IMAP is first pressed on the skin to create microholes and then is retracted, followed by the iontophoresis delivery of insulin-loaded nanovesicles through these microholes in an electrically controlled manner. This method has synergistically and remarkably enhanced controlled insulin delivery. The amount of insulin can be effectively regulated by the IMAP by applying different current intensities. This in vivo study has demonstrated that the IMAP effectively delivers insulin and produces robust hypoglycemic effects in a type-1 diabetic rat model, with more advanced controllability and efficiency than delivery by a pristine microneedle or iontophoresis. The IMAP system shows high potential for diabetes therapy and the capacity to provide active as well as long-term glycemic regulation without medical staff care.

Nanotechnology in Insulin Delivery for Management of Diabetes

Diabetes is a group of diseases characterized by hyperglycemia and originating from the deficiency or resistance to insulin, or both. Ultimately, the most effective treatment for patients with diabetes involves subcutaneous injections of insulin. However, this route of administration is often painful and inconvenient, as most patients will have to selfadminister it at least twice a day for the rest of their lives. Also, infection, insulin precipitation, and either lipoatrophy or lipohypertrophy are frequently observed at the site of injection. To date, several alternative routes of insulin administration have been explored, including nasal, pulmonary and oral. Although the delivery of insulin is an ideal route for diabetic patients, several limitations have to be overcome such as the rapid degradation of insulin in gastric fluid and low oral bioavailability. Numerous strategies have been carried out to improve these limited parameters such as the use of enzyme inhibitors, absorption enhancers, mucoadhesive polymers and chemical modification for receptor-mediated absorption. Also, insulin-loaded nanocarriers bypass several physiological barriers. This current review focuses on the various barriers existing in the delivery of insulin through the oral route and the strategies undertaken so far to overcome those obstacles using nanocarriers as a potential vehicle of insulin.

A forskolin-conjugated insulin analog targeting endogenous glucose-transporter for glucose-responsive insulin delivery

Insulin administration for the management of diabetes is accompanied by hypoglycemia, which is expected to be mitigated by glucose-responsive smart insulin that has self-regulation ability in response to blood glucose level (BGL) fluctuation. Here, we have prepared a new insulin analog by modifying insulin with forskolin (designated as insulin-F), a glucose-transporter (Glut) inhibitor. In vitro, insulin-F is capable of binding to Glut on erythrocyte ghosts, which can be inhibited by glucose and cytochalasin B. Upon subcutaneous injection in type 1 diabetic mice, insulin-F maintains BGLs below 200 mg mL-1 for up to 10 h, and achieves 20 h with two sequential injections. Moreover, insulin-F also binds to endogenous Gluts. Upon a glucose challenge, the elevated level of glucose competitively replaces and liberates insulin-F that binds to Glut, rapidly restoring BGLs to the normal range.

Effects of Periodic Intensive Insulin Therapy: An Updated Review

Background

Traditional insulin treatment for diabetes mellitus with insulin administered subcutaneously yields nonpulsatile plasma insulin concentrations that represent a fraction of normal portal vein levels. Oral hypoglycemic medications result in the same lack of pulsatile insulin response to blood glucose levels. Intensive treatments of significant complications of diabetes are not recommended due to complicated multidrug regimens, significant weight gain, and the high risk of hypoglycemic complications. Consequently, advanced complications of diabetes do not have an effective treatment option because conventional therapy is not sufficient. Intensive insulin therapy (IIT) simulates normal pancreatic function by closely matching the periodicity and amplitude of insulin secretion in healthy subjects; however, the mechanisms involved with the observed improvement are not clearly understood.

Objective

The current review aims to analyze the pathophysiology of insulin secretion, discuss current therapies for the management of diabetes, provides an updates on the recent advancements of IIT, and proposes its mechanism of action.

Methods

A literature search on PubMed, MEDLINE, Embase, and CrossRef databases was performed on multiple key words regarding the history and current variations of pulsatile and IIT for diabetes treatment. Articles reporting the physiology of insulin secretion, advantages of pulsatile insulin delivery in patients with diabetes patients, efficacy and adverse effects of current conventional insulin therapies for the management of diabetes, benefits and shortcomings of pancreas and islet transplantation, or clinical trials on patients with diabetes treated with pulsed insulin therapy or advanced IIT were included for a qualitative analysis and categorized into the following topics: mechanism of insulin secretion in normal subjects and patients with diabetes and current therapies for the management of diabetes, including oral hypoglycemic agents, insulin therapy, pancreas and islet transplantation, pulsed insulin therapy, and advances in IIT.

Results

Our review of the literature shows that IIT improves the resolution of diabetic ulcers, neuropathy, and nephropathy, and reduces emergency room visits. The likely mechanism responsible for this improvement is increased insulin sensitivity from adipocytes, as well as increased insulin receptor expression.

Conclusions

Recent advancements show that IIT is an effective option for both type 1 diabetes mellitus and type 2 diabetes mellitus patient populations. This treatment resembles normal pancreatic function so closely that it has significantly reduced the effects of relatively common complications of diabetes in comparison to standard treatments. Thus, this new treatment is a promising advancement in the management of diabetes. (Curr Ther Res Clin Exp. 2019; 80:XXX–XXX).

Glucose-responsive insulin by molecular and physical design

The concept of a glucose-responsive insulin (GRI) has been a recent objective of diabetes technology. The idea behind the GRI is to create a therapeutic that modulates its potency, concentration or dosing relative to a patient's dynamic glucose concentration, thereby approximating aspects of a normally functioning pancreas. From the perspective of the medicinal chemist, the GRI is also important as a generalized model of a potentially new generation of therapeutics that adjust potency in response to a critical therapeutic marker. The aim of this Perspective is to highlight emerging concepts, including mathematical modelling and the molecular engineering of insulin itself and its potency, towards a viable GRI. We briefly outline some of the most important recent progress toward this goal and also provide a forward-looking viewpoint, which asks if there are new approaches that could spur innovation in this area as well as to encourage synthetic chemists and chemical engineers to address the challenges and promises offered by this therapeutic approach.