Monomeric insulins and their experimental and clinical implications

Injectable systems for long-lasting insulin therapy

Insulin therapy is the mainstay to treat diabetes characterizedd by hyperglycemia. However, its short half-life of only 4-6 min limits its effectiveness in treating chronic diabetes. Advances in recombinant DNA technology and protein engineering have led to several insulin analogue products that have up to 42 h of glycemic control. However, these insulin analogues still require once- or twice-daily injections for optimal glycemic control and have poor patient compliance and adherence issues. To achieve insulin release for more than one day, different injectable delivery systems including microspheres, in situ forming depots, nanoparticles and composite systems have been developed. Several of these delivery systems have advanced to clinical trials for once-weekly insulin injection. This review comprehensively summarizes the developments of injectable insulin analogs and delivery systems covering the whole field of injectable long-lasting insulin technologies from prototype design, preclinical studies, clinical trials to marketed products for the treatment of diabetes.

Staphylococcal protein A-modified hydrogel facilitates in situ immunomodulation by capturing anti-HMGB1 for islet grafts

Islet transplantation is regarded as the most promising therapy for type 1 diabetes. However, both hypoxia and immune attack impair the grafted islets after transplantation, eventually failing the islet graft. Although many studies showed that biomaterials with nanoscale pores, like hydrogels, could protect islets from immune cells, the pores on biomaterials inhibited vascular endothelial cells (VECs) to creep in, which resulted in poor revascularization. Thus, a hydrogel device that can facilitate in situ immune modulations without the cost of poor revascularization should be put forward. Accordingly, we designed a spA-modified hydrogel capturing anti-HMGB1 mAB (mAB-spA Gel): the Staphylococcus aureus protein A (spA) was conjugated on the network of hydrogel to capture anti-HMGB1mAB which can inactivate immune cells, while the pore sizes of the hydrogel were more than 100μm which allows vascular endothelial cells (VECs) to creep in. In this study, we screened the optimal spA concentration in mAB-spA Gel according to the physical properties and antibody binding capability, then demonstrated that it could facilitate in situ immunomodulation without decreasing the vessel reconstruction in vitro. Further, we transplanted islet graft in vivo and showed that the survival of islets was elongated. In conclusion, mAB-spA Gel provided an alternative islet encapsulation strategy for type 1 diabetes. STATEMENT OF SIGNIFICANCE: Although various studies have shown that the backbone of the hydrogels can isolate islets grafts from immune cells and the survival of the islets can be prolonged by this way, it is also reported that when the pore size of the backbone is too small the revascularization will be adversely affected. According to this point, it is hard to adjust hydrogel's pore size to protect the islets from the immune attack while allowing endothelial vascular cells to creep in. To solve this dilemma, we designed an immunomodulatory hydrogel inhibiting the activation of T cells by immunosuppressive IgGs instead of the backbone network, so the hydrogel can prolong the survival of islets without the sacrifice of revascularization.

Accelerated absorption of regular insulin administered via a vascularizing permeable microchamber implanted subcutaneously in diabetic Rattus norvegicus

In Type 1 diabetes patients, even ultra-rapid acting insulins injected subcutaneously reach peak concentrations in 45 minutes or longer. The lag time between dosing and peak concentration, as well as intra- and inter-subject variability, render prandial glucose control and dose consistency difficult. We postulated that insulin absorption from subcutaneously implantable vascularizing microchambers would be significantly faster than conventional subcutaneous injection. Male athymic nude R. norvegicus rendered diabetic with streptozotocin were implanted with vascularizing microchambers (single chamber; 1.5 cm2 surface area per side; nominal volume, 22.5 μl). Plasma insulin was assayed after a single dose (1.5 U/kg) of diluted insulin human (Humulin®R U-100), injected subcutaneously or via microchamber. Microchambers were also implanted in additional animals and retrieved at intervals for histologic assessment of vascularity. Following conventional subcutaneous injection, the mean peak insulin concentration was 22.7 (SD 14.2) minutes. By contrast, when identical doses of insulin were injected via subcutaneous microchamber 28 days after implantation, the mean peak insulin time was shortened to 7.50 (SD 4.52) minutes. Peak insulin concentrations were similar by either route; however, inter-subject variability was reduced when insulin was administered via microchamber. Histologic examination of tissue surrounding microchambers showed mature vascularization on days 21 and 40 post-implantation. Implantable vascularizing microchambers of similar design may prove clinically useful for insulin dosing, either intermittently by needle, or continuously by pump including in "closed loop" systems, such as the artificial pancreas.

FK506-Binding Protein 2 Participates in Proinsulin Folding

Apart from chaperoning, disulfide bond formation, and downstream processing, the molecular sequence of proinsulin folding is not completely understood. Proinsulin requires proline isomerization for correct folding. Since FK506-binding protein 2 (FKBP2) is an ER-resident proline isomerase, we hypothesized that FKBP2 contributes to proinsulin folding. We found that FKBP2 co-immunoprecipitated with proinsulin and its chaperone GRP94 and that inhibition of FKBP2 expression increased proinsulin turnover with reduced intracellular proinsulin and insulin levels. This phenotype was accompanied by an increased proinsulin secretion and the formation of proinsulin high-molecular-weight complexes, a sign of proinsulin misfolding. FKBP2 knockout in pancreatic β-cells increased apoptosis without detectable up-regulation of ER stress response genes. Interestingly, FKBP2 mRNA was overexpressed in β-cells from pancreatic islets of T2D patients. Based on molecular modeling and an in vitro enzymatic assay, we suggest that proline at position 28 of the proinsulin B-chain (P28) is the substrate of FKBP2's isomerization activity. We propose that this isomerization step catalyzed by FKBP2 is an essential sequence required for correct proinsulin folding.

Formation of Protamine and Zn-Insulin Assembly: Exploring Biophysical Consequences

The insulin-protamine interaction is at the core of the mode of action in many insulin formulations (Zn + insulin + protamine) and to treat diabetes, in which protamine is added to the stable form of hexameric insulin (Zn-insulin). However, due to the unavailability of quantitative data and a high-resolution structure, the binding mechanism of the insulin-protamine complex remains unknown. In this study, it was observed that Zn-insulin experiences destabilization as observed by the loss of secondary structure in circular dichroism (CD), and reduction in thermal stability in melting study, upon protamine binding. In isothermal titration calorimetry (ITC), it was found that the interactions were mostly enthalpically driven. This is in line with the positive ΔC _m value (+880 cal mol^-1), indicating the role of hydrophilic interactions in the complex formation, with the exposure of hydrophobic residues to the solvent, which was firmly supported by the 8-anilino-1-naphthalene sulfonate (ANS) binding study. The stoichiometry (N) value in ITC suggests the multiple insulin molecules binding to the protamine chain, which is consistent with the picture of the condensation of insulin in the presence of protamine. Atomic force microscopy (AFM) suggested the formation of a heterogeneous Zn-insulin-protamine complex. In fluorescence, Zn-insulin experiences strong Tyr quenching, suggesting that the location of the protamine-binding site is near Tyr, which is also supported by the molecular docking study. Since Tyr is critical in the stabilization of insulin self-assembly, its interaction with protamine may impair insulin's self-association ability and thermodynamic stability while at the same time promoting its flexible conformation desired for better biological activity.

Subtle pH variation around pH 4.0 affects aggregation kinetics and aggregate characteristics of recombinant human insulin

Insulin is a biotherapeutic protein, which, depending on environmental conditions such as pH, has been shown to form a large variety of aggregates with different structures and morphologies. This work focuses on the formation and characteristics of insulin particulates, dense spherical aggregates having diameters spanning from nanometre to low-micron size. An in-depth investigation of the system is obtained by applying a broad range of techniques for particle sizing and characterisation. An interesting observation was achieved regarding the formation kinetics and aggregate characteristics of the particulates; a subtle change in the pH from pH 4.1 to pH 4.3 markedly affected the kinetics of the particulate formation and led to different particulate sizes, either nanosized or micronsized particles. Also, a clear difference between the secondary structure of the protein particulates formed at the two pH values was observed, where the nanosized particulates had an increased content of aggregated β-structure compared to the micronsized particles. The remaining characteristics of the particles were identical for the two particulate populations. These observations highlight the importance of carefully studying the formulation design space and of knowing the impact of parameters such as pH on the aggregation to secure a drug product in control. Furthermore, the identification of particles only varying in few parameters, such as size, are considered highly valuable for studying the effect of particle features on the immunogenicity potential.

Characterization and impact of peptide physicochemical properties on oral and subcutaneous delivery

Peptides, an emerging modality within the biopharmaceutical industry, are often delivered subcutaneously with evolving prospects on oral delivery. Barrier biology within the subcutis or gastrointestinal tract is a significant challenge in limiting absorption or otherwise disrupting peptide disposition. Aspects of peptide pharmacokinetic performance and ADME can be mitigated with careful molecular design that tailors for properties such as effective size, hydrophobicity, net charge, proteolytic stability, and albumin binding. In this review, we endeavor to highlight effective techniques in qualifying physicochemical properties of peptides and discuss advancements of in vitro models of subcutaneous and oral delivery. Additionally, we will delineate empirical findings around the relationship of these physicochemical properties and in vivo (animal or human) impact. We conclude that robust peptide characterization methods and in vitro techniques with demonstrated correlations to in vivo data are key routines to incorporate in the drug discovery and development to improve the probability of technical and commercial success of peptide therapeutics.

Progress in Simulation Studies of Insulin Structure and Function

Insulin is a peptide hormone known for chiefly regulating glucose level in blood among several other metabolic processes. Insulin remains the most effective drug for treating diabetes mellitus. Insulin is synthesized in the pancreatic β-cells where it exists in a compact hexameric architecture although its biologically active form is monomeric. Insulin exhibits a sequence of conformational variations during the transition from the hexamer state to its biologically-active monomer state. The structural transitions and the mechanism of action of insulin have been investigated using several experimental and computational methods. This review primarily highlights the contributions of molecular dynamics (MD) simulations in elucidating the atomic-level details of conformational dynamics in insulin, where the structure of the hormone has been probed as a monomer, dimer, and hexamer. The effect of solvent, pH, temperature, and pressure have been probed at the microscopic scale. Given the focus of this review on the structure of the hormone, simulation studies involving interactions between the hormone and its receptor are only briefly highlighted, and studies on other related peptides (e.g., insulin-like growth factors) are not discussed. However, the review highlights conformational dynamics underlying the activities of reported insulin analogs and mimetics. The future prospects for computational methods in developing promising synthetic insulin analogs are also briefly highlighted.

Insulin regulates arginine-stimulated insulin secretion in humans

AIMS

Insulin potentiates glucose-stimulated insulin secretion. These effects are attenuated in beta cell-specific insulin receptor knockout mice and insulin resistant humans. This investigation examines whether short duration insulin exposure regulates beta cell responsiveness to arginine, a non-glucose secretagogue, in healthy humans.

MATERIALS AND METHODS

Arginine-stimulated insulin secretion was studied in 10 healthy humans. In each subject arginine was administered as a bolus followed by continuous infusion on two occasions one month apart, after sham/saline or hyperinsulinemic-isoglycemic clamp, respectively providing low and high insulin pre-exposure conditions. Arginine-stimulated insulin secretion was measured by C-peptide deconvolution, and by a selective immunogenic (DAKO) assay for direct measurement of endogenous but not exogenous insulin.

RESULTS

Pre-exposure to exogenous insulin augmented arginine-stimulated insulin secretion. The effect was seen acutely following arginine bolus (endogenous DAKO insulin incremental AUC_240-255min 311.6 ± 208.1 (post-insulin exposure) versus 120.6 ± 42.2 μU/ml•min (sham/saline) (t-test P = 0.021)), as well as in response to continuous arginine infusion (DAKO insulin incremental AUC_260-290min 1095.3 ± 592.1 (sham/saline) versus 564.8 ± 207.1 μU/ml•min (high insulin)(P = 0.009)). Findings were similar when beta cell response was assessed using C-peptide, insulin secretion rates by deconvolution, and the C-peptide to glucose ratio.

CONCLUSIONS

We demonstrate a physiologic role of insulin in regulation of the beta cell secretory response to arginine.

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.

One-hundred year evolution of prandial insulin preparations: From animal pancreas extracts to rapid-acting analogs

The first insulin preparation injected in humans in 1922 was short-acting, extracted from animal pancreas, contaminated by impurities. Ever since the insulin extracted from animal pancreas has been continuously purified, until an unlimited synthesis of regular human insulin (RHI) became possible in the '80s using the recombinant-DNA (rDNA) technique. The rDNA technique then led to the designer insulins (analogs) in the early '90s. Rapid-acting insulin analogs were developed to accelerate the slow subcutaneous (sc) absorption of RHI, thus lowering the 2-h post-prandial plasma glucose (PP-PG) and risk for late hypoglycemia as comparing with RHI. The first rapid-acting analog was lispro (in 1996), soon followed by aspart and glulisine. Rapid-acting analogs are more convenient than RHI: they improve early PP-PG, and 24-h PG and A1C as long as basal insulin is also optimized; they lower the risk of late PP hypoglycemia and they allow a shorter time-interval between injection and meal. Today rapid-acting analogs are the gold standard prandial insulins. Recently, even faster analogs have become available (faster aspart, ultra-rapid lispro) or are being studied (Biochaperone lispro), making additional gains in lowering PP-PG. Rapid-acting analogs are recommended in all those with type 1 and type 2 diabetes who need prandial insulin replacement.

Enhanced Skin Delivery of Therapeutic Peptides Using Spicule-Based Topical Delivery Systems

This study reports two therapeutic peptides, insulin (INS, as a hydrophilic model peptide) and cyclosporine A (CysA, as a hydrophobic one), that can be administrated through a transdermal or dermal route by using spicule-based topical delivery systems in vitro and in vivo. We obtained a series of spicules with different shapes and sizes from five kinds of marine sponges and found a good correlation between the skin permeability enhancement induced by these spicules and their aspect ratio L/D. In the case of INS, Sponge Haliclona sp. spicules (SHS) dramatically increased the transdermal flux of INS (457.0 ± 32.3 ng/cm²/h) compared to its passive penetration (5.0 ± 2.2 ng/cm²/h) in vitro. Further, SHS treatment slowly and gradually reduced blood glucose to 13.1 ± 6.3% of the initial level in 8 h, while subcutaneous injection resulted in a rapid blood glucose reduction to 15.9 ± 1.4% of the initial level in 4 h, followed by a rise back to 75.1 ± 24.0% of the initial level in 8 h. In the case of CysA, SHS in combination with ethosomes (SpEt) significantly (p < 0.05) increased the accumulation of CysA in viable epidermis compared to other groups. Further, SpEt reduced the epidermis thickness by 41.5 ± 9.4% in 7 days, which was significantly more effective than all other groups. Spicule-based topical delivery systems offer promising strategies for delivering therapeutic peptides via a transdermal or dermal route.

Modeling Between-Subject Variability in Subcutaneous Absorption of a Long-Acting Insulin Glargine 100 U/mL by a Nonlinear Mixed Effects Approach

Subcutaneous insulin absorption is well-known to vary significantly both between and within subjects (BSV and WSV, respectively). This variability considerably obstacles the establishing of a reproducible and effective insulin therapy. Some models exist to describe the subcutaneous kinetics of both fast and long-acting insulin analogues; however, none of them account for the BSV. The aim of this study is to develop a nonlinear mixed effects model able to describe the BSV observed in the subcutaneous absorption of a long-acting insulin glargine 100 U/mL. Four stochastic models of the BSV were added to a previously validated model of subcutaneous absorption of insulin glargine 100 U/mL. These were assessed on a database of 47 subjects with type 1 diabetes. The best model was selected based on residual analysis, precision of the estimates and parsimony criteria. The selected model provided good fit of individual data, precise population parameter estimates and allowed quantifying the BSV of the insulin glargine 100 U/mL pharmacokinetics. Future model development will include the description of the WSV of long- acting insulin absorption.

100 Years of Insulin: Lifesaver, immune target, and potential remedy for prevention

In this review, we bring our personal experiences to showcase insulin from its breakthrough discovery as a life-saving drug 100 years ago to its uncovering as the autoantigen and potential cause of type 1 diabetes and eventually as an opportunity to prevent autoimmune diabetes. The work covers the birth of insulin to treat patients, which is now 100 years ago, the development of human insulin, insulin analogues, devices, and the way into automated insulin delivery, the realization that insulin is the primary autoimmune target of type 1 diabetes in children, novel approaches of immunotherapy using insulin for immune tolerance induction, the possible limitations of insulin immunotherapy, and an outlook how modern vaccines could remove the need for another 100 years of insulin therapy.

A Comprehensive Review of Intranasal Insulin and Its Effect on the Cognitive Function of Diabetics

Diabetes mellitus continues to be a disease that affects a good percentage of our population. The majority affected need insulin on a day-to-day basis. Before the invention of the first manufactured insulin in 1978, dealing with diabetes took a significant toll on patient's lives. As technology and human innovation prevail, significant advancements have taken place in managing this chronic disease. Patients have an option to decide their mode of insulin delivery. Intranasal insulin, one such form, has a rapid mode of action while effectively controlling postprandial hyperglycemia. It has also been proven to reduce hypoglycemia and insulin resistance problems, which seem to be the main adverse effects of using conventional insulin regularly. However, due to the large dosages needed and high incurring costs, Intranasal Insulin is currently being used as adjunctive therapy along with conventional insulin.  We conducted a literature search in PubMed indexed journals using the medical terms "Intranasal insulin," "diabetes," and "cognitive impairment" to provide an overview of the mechanism of action of Intranasal Insulin, its distinctive cognitive benefits, and how it can be compared to the standard parenteral insulin therapy. One unique feature of intranasal insulin is its ability to directly affect the central nervous system, bypassing the blood-brain barrier. Not only does this help in reducing the peripheral side effects of insulin, but it has also proven to play a role in improving the cognitive function of diabetics, especially those who have Alzheimer's or mild cognitive impairment, as decreased levels of insulin in the brain has been shown to impact cognitive function negatively. However, it does come with its limitations of poor absorption through the nasal mucosa due to mucociliary clearance and proteolytic enzymes, our body's natural defence mechanisms. This review focuses on the efficacy of intranasal insulin, its potential benefits, limitations, and role in cognitive improvement in people with diabetes with pre-existing cognitive impairment.

Phenolic Preservative Removal from Commercial Insulin Formulations Reduces Tissue Inflammation while Maintaining Euglycemia

Background: Exogenous insulin therapy requires stabilization of the insulin molecule, which is achieved through the use of excipients (e.g., phenolic preservatives (PP)) that provide protein stability, sterility and prolong insulin shelf life. However, our laboratory recently reported that PP, (e.g., m-creosol and phenol) are also cytotoxic, inducing inflammation and fibrosis. Optimizing PP levels through filtration would balance the need for insulin preservation with PP-induced inflammation. Method: Zeolite Y (Z-Y), a size-exclusion-based resin, was employed to remove PP from commercial insulin formulations (Humalog) before infusion. Results: PP removal significantly decreased cell toxicity in vitro and inflammation in vivo. Infusion site histological analysis after a 3 day study demonstrated that leukocyte accumulation increased with nonfiltered preparations but decreased after filtration. Additional studies demonstrated that a Z-Y fabricated filter effectively removed excess PP such that the filtered insulin solution achieved equivalent glycemic control in diabetic mice when compared to nonfiltered insulin. Conclusion: This approach represents the proof of concept that using Z-Y for in-line PP removal assists in lowering inflammation at the site of insulin infusion and thus could lead to extending the functional lifespan of insulin infusion sets in vivo.

Modeling Between-Subject Variability in Subcutaneous Absorption of a Fast-Acting Insulin Analogue by a Nonlinear Mixed Effects Approach

Despite the great progress made in insulin preparation and titration, many patients with diabetes are still experiencing dangerous fluctuations in their blood glucose levels. This is mainly due to the large between- and within-subject variability, which considerably hampers insulin therapy, leading to defective dosing and timing of the administration process. In this work, we present a nonlinear mixed effects model describing the between-subject variability observed in the subcutaneous absorption of fast-acting insulin. A set of 14 different models was identified on a large and frequently-sampled database of lispro pharmacokinetic data, collected from 116 subjects with type 1 diabetes. The tested models were compared, and the best one was selected on the basis of the ability to fit the data, the precision of the estimated parameters, and parsimony criteria. The selected model was able to accurately describe the typical trend of plasma insulin kinetics, as well as the between-subject variability present in the absorption process, which was found to be related to the subject’s body mass index. The model provided a deeper understanding of the insulin absorption process and can be incorporated into simulation platforms to test and develop new open- and closed-loop treatment strategies, allowing a step forward toward personalized insulin therapy.

Interindividual Variability in the Pharmacodynamic and Pharmacokinetic Characteristics of Recombinant Human Insulin and Insulin Aspart

PURPOSE

The present study compared the interindividual variability in the pharmacodynamic (PD) and pharmacokinetic (PK) properties of a short-acting recombinant human insulin to those of insulin aspart through manual euglycemic glucose clamp tests.

METHODS

Sixty healthy Chinese male volunteers were randomly assigned to receive human insulin or insulin aspart, administered via SC injection (0.2 U/kg). For the evaluation of interindividual variability in PD and PK properties (glucose infusion rate [GIR], insulin concentration [INS]) through euglycemic clamp studies, %CVs were calculated, and PK/PD interindividual variability was compared between the 2 groups.

FINDINGS

The differences between the human insulin and insulin aspart groups in interindividual variabilities in total AUCs of the GIR (19% vs 21%) and INS (14% vs 17%) were not significant. The interindividual variabilities in AUCgir_0-120min, early T_max50%, and AUCins_0-120min were lower in the insulin aspart group than in the human insulin group (22% vs 44%, 21% vs 35%, and 22% vs 28%, respectively; all, P ˂ 0.05), while the interindividual variabilities in the AUCs of GIR_120-600min and INS_120-600min were higher with insulin aspart than with human insulin (29% vs 20%, 51% vs 30%; both, P ˂ 0.05).

IMPLICATIONS

The overall interindividual variability with insulin aspart was similar to that with recombinant human insulin. Yet insulin concentration and metabolic effect during the declining period were more variable with insulin aspart compared to human insulin in these healthy male subjects.

Improving the treatment of patients with diabetes using insulin analogues: current findings and future directions

Introduction: The aim of insulin replacement in insulin-deficient people (type 1 diabetes, pancreatic causes of diabetes, long-standing type 2 diabetes) is to approximate the physiologic insulin action profile as closely as possible. However, short-acting human insulins start too slow and act too long, causing postprandial hyperglycemia and delayed hypoglycemia, while the insulin action profile of long-acting human insulins is too variable in duration and strength of action, leading to insufficient basal insulin covering and peak insulin levels after injection causing early nocturnal hypoglycemia. Insulin analogues were designed to overcome these shortcomings. In insulin-resistant people (type 2 diabetes), insulin analogues contribute to more efficient and safer insulin supplementation. Areas covered: In this review, we describe the unmet needs for insulin therapy, the currently available short- and long-acting insulin analogues and some considerations on cardiovascular outcomes, use in special populations, and cost-effectiveness. Finally, we discuss what is new in the field of insulin analogues. Expert opinion: The development of insulin analogues is an important step in diabetes treatment. Despite many patients meeting their glycemic targets with the newest analogues, hypoglycemic episodes remain a major problem. More physiologic insulin regimens, with glucose-sensitive or organ-targeting insulin analogues may be the answer to these issues.

Shortcut Approaches to Substance Delivery into the Brain Based on Intranasal Administration Using Nanodelivery Strategies for Insulin

The direct delivery of central nervous system (CNS) drugs into the brain after administration is an ideal concept due to its effectiveness and non-toxicity. However, the blood-brain barrier (BBB) prevents drugs from penetrating the capillary endothelial cells, blocking their entry into the brain. Thus, alternative approaches must be developed. The nasal cavity directly leads from the olfactory epithelium to the brain through the cribriform plate of the skull bone. Nose-to-brain drug delivery could solve the BBB-related repulsion problem. Recently, it has been revealed that insulin improved Alzheimer's disease (AD)-related dementia. Several ongoing AD clinical trials investigate the use of intranasal insulin delivery. Related to the real trajectory, intranasal labeled-insulins demonstrated distribution into the brain not only along the olfactory nerve but also the trigeminal nerve. Nonetheless, intranasally administered insulin was delivered into the brain. Therefore, insulin conjugates with covalent or non-covalent cargos, such as AD or other CNS drugs, could potentially contribute to a promising strategy to cure CNS-related diseases. In this review, I will introduce the CNS drug delivery approach into the brain using nanodelivery strategies for insulin through transcellular routes based on receptor-mediated transcytosis or through paracellular routes based on escaping the tight junction at the olfactory epithelium.

Are newer insulin analogues better for people with Type 1 diabetes?

Achieving optimal blood glucose control in Type 1 diabetes is a delicate balance between ensuring tight glycaemic control and achieving this without the expense of hypoglycaemia and weight gain, two major factors impacting quality of life. This is a real challenge for people with Type 1 diabetes and underpins many of the struggles they face in self-managing on a day-to-day basis. The main goals of insulin delivery are to try to simulate the physiology of β-cell insulin secretion as closely as possible and to overcome the challenges of peripheral insulin administration by achieving rapidity of onset with mealtime insulins and stability of the glucose-lowering effects of long-acting insulins. Since the early days of human insulin use, there have been many developments in insulin formulations that aim to achieve these goals as much as possible, thus contributing to better glycaemic control whilst minimizing hypoglycaemia. In the present review we discuss the currently available insulin analogues and the challenges of achieving glucose control using current analogues in those on multiple daily injections, and appraise the evidence base for newer-generation insulin analogues, such as insulin degludec, glargine U300, faster-acting insulin aspart and BioChaperone lispro. We also highlight new insulins in development and unmet needs in people with Type 1 diabetes.

Inter-protein interactions govern protein loading into porous vaterite CaCO3 crystals

Loading of therapeutic proteins into mesoporous vaterite crystals is driven by inter-protein interactions in bulk solution and inside the crystals.

Investigation of factors that cause insulin precipitation and/or amyloid formation in insulin formulations

Background

Multiple daily subcutaneous injections (MDSIs) are mainly used for formulating an insulin therapy for diabetic patients; however, they also cause insulin-derived amyloidosis (IDA) and lead to poor glycemic control. In addition, for the continuous subcutaneous insulin infusion system (CSII), precipitation frequently causes catheter occlusion and, if the precipitate in the formulations is amyloid, the injection of the insoluble amyloid into the subcutaneous tissue leads to IDA. The aim of this study was to conduct in vitro experiments and present a situation where insulin formulations cause precipitation and amyloid formation.

Methods

Humulin®R and NovoRapid® were used as model formulations for MDSIs and CSII, respectively. The generation of the precipitation was evaluated by measuring turbidity, and amyloid formation was evaluated by using Thioflavin T. Humulin®R was mixed with saline buffer solutions and glucose solutions to evaluate the effect of dilution. In addition, we created an experimental system to consider the effect of the time course of condition changes, and investigated the effects of insulin concentration, m-cresol existence, and pH change on the generation of the precipitate and amyloid in the formulation.

Results

In both the original and diluted formulations, physical stimulation resulted in the formation of a precipitate, which in most cases was an amyloid. The amyloid was likely to be formed at a near neutral pH. On the contrary, although a precipitate formed when the pH was decreased to near the isoelectric point, this precipitate was not an amyloid. Further decreases in pH resulted in the formation of amyloids, suggesting that both the positive and negative charged states of insulin tended to form amyloids. The formulation additive m-cresol suppressed amyloid formation. When additives were removed from the formulation, the amyloid-containing gel was formed in the field of substance exchange.

Conclusions

To consider changes in conditions that may occur for insulin formulations, the relationship between the formation of precipitates and amyloids was demonstrated in vitro by using insulin formulations. From the in vitro study, m-cresol was shown to have an inhibitory effect on amyloid formation.

The quaternary structure of insulin glargine and glulisine under formulation conditions

The quaternary structures of insulin glargine and glulisine under formulation conditions and upon dilution using placebo or water were investigated using synchrotron small-angle X-ray scattering. Our results revealed that insulin glulisine in Apidra® is predominantly hexameric in solution with significant fractions of dodecamers and monomers. Upon dilution with placebo, this equilibrium shifts towards monomers. Insulin glargine in Lantus® and Toujeo® is present in a stable hexamer/dimer equilibrium, which is hardly affected by dilution with water down to 1 mg/ml insulin concentration. The results provide exclusive insight into the quaternary structure and thus the association/dissociation properties of the two insulin analogues in marketed formulations.

Pharmacologic treatment options for type 1 diabetes: what's new?

INTRODUCTION

The expanding variety of insulins, including biosynthetic human insulin and rapid and long-acting insulin analogs, have dramatically transformed the management of type 1 diabetes (T1D) over the past 25 years. Moreover, increasing interest in the use of novel drugs developed for the treatment of type 2 diabetes (T2D) as adjunctive therapies for T1D remains a work in progress. Areas Covered: We reviewed articles published up to December 2018 in PubMed and ClinicalTrials.gov for recent developments in the pharmacologic treatment of T1D, including inhaled insulin, ultrafast and ultralong-acting insulins and adjunctive therapies including pramlintide, metformin, GLP-1 receptor agonists, DPP-4 inhibitors, SGLT-2, and SGLT1/2 inhibitors. Expert Opinion: With the creation of ultrafast-acting insulin analogs and very prolonged duration of action of basal insulins, it is possible to more closely mimic physiologic insulin secretion. Adjunctive therapies, likewise, may also overcome some of the abnormal physiology that is a hallmark of T1D. Therefore, individualized consideration of the efficacy of these agents must be measured alongside the potential adverse effects when choosing an adjunctive therapy.

Insulin Units and Conversion Factors: A Story of Truth, Boots, and Faster Half-Truths

Conventional insulin concentration units (IU/mL or just U/mL) are bioefficacy based, whereas the Système International (SI) units (pmol/L) are mass based. In converting between these two different approaches, there are at least 2 well-accepted conversion factors, where there should be only 1. The correct value is not the most-used or well-accepted using online calculators, some journal styles, laboratory reports, and published articles. In short, an incorrect insulin conversion factor is widely used which underreports insulin concentrations by ~15%, with potentially significant research and clinical implications. This short commentary describes the history of insulin IU definitions and conversion factors, and highlights the widespread nature of conversion factor misuse, to provoke deeper interest and thought regarding numbers we so often use without thinking.

Nanotechnology in cell replacement therapies for type 1 diabetes

Islet transplantation is a promising long-term, compliance-free, complication-preventing treatment for type 1 diabetes. However, islet transplantation is currently limited to a narrow set of patients due to the shortage of donor islets and side effects from immunosuppression. Encapsulating cells in an immunoisolating membrane can allow for their transplantation without the need for immunosuppression. Alternatively, "open" systems may improve islet health and function by allowing vascular ingrowth at clinically attractive sites. Many processes that enable graft success in both approaches occur at the nanoscale level-in this review we thus consider nanotechnology in cell replacement therapies for type 1 diabetes. A variety of biomaterial-based strategies at the nanometer range have emerged to promote immune-isolation or modulation, proangiogenic, or insulinotropic effects. Additionally, coating islets with nano-thin polymer films has burgeoned as an islet protection modality. Materials approaches that utilize nanoscale features manipulate biology at the molecular scale, offering unique solutions to the enduring challenges of islet transplantation.

Key Physicochemical Characteristics Influencing ADME Properties of Therapeutic Proteins

Therapeutic proteins are a rapidly growing class of drugs in clinical settings. The pharmacokinetics (PK) of therapeutic proteins relies on their absorption, distribution, metabolism, and excretion (ADME) properties. Moreover, the ADME properties of therapeutic proteins are impacted by their physicochemical characteristics. Comprehensive evaluation of these characteristics and their impact on ADME properties are critical to successful drug development. This chapter summarizes all relevant physicochemical characteristics and their effect on ADME properties of therapeutic proteins.

Enhanced intranasal insulin delivery by formulations and tumor protein-derived protein transduction domain as an absorption enhancer

One of the key factors for successful development of an intranasal insulin formulation is an absorption enhancer that would deliver insulin efficiently across nasal membranes without causing damage to mucosa or inducing protein aggregation under physiological conditions. In the present study, a protein transduction domain (PTD1) and its L-form with the double substitution A6L and I8A (PTD4), derived from human translationally controlled tumor protein, were used as absorption enhancers. PTD4 exhibited higher compatibility with insulin in terms of biophysical properties analyzed using μDSC, DLS, and CD. In addition, thermodynamic properties indicated stable complex formation but higher propensity of protein aggregation. Arginine hydrochloride (ArgHCl) was used to suppress protein aggregation and carbohydrates (i.e., mannitol, sucrose, and glycerin) were used as osmolytes in the formulation. The relative bioavailability of insulin co-administered intranasally using PTD4, 16 mg/mL glycerin and 100 mM ArgHCl was 58% and that using PTD4, 1 w/v% sucrose, and 25 mM ArgHCl was 53% of the bioavailability obtained via the subcutaneous route. These values represented a remarkable increase in bioavailability of intranasal insulin, causing a significant decrease in blood glucose levels within one hour. The pharmacokinetic properties of intranasal absorption were dependent on the concentration of carbohydrates used. These results suggest that the newly designed formulations with PTD represent a useful platform for intranasal delivery of insulin and other biomolecules.

In vitro assessment of the influence of intravenous extension set materials on insulin aspart drug delivery

Insulin is a frequently prescribed drug in hospitals and is usually administered by syringe pumps with an extension line which can be made of various materials. Two insulin solutions were studied: an insulin analogue, Novorapid^® which contains insulin aspart and two phenolic preservatives (e.g. phenol and metacresol) and Umuline rapide^® with human insulin and metacresol as preservative. Some studies have indicated interactions between insulin, polyvinyl chloride (PVC) and polyethylene (PE). The aim of this work was to study such interactions between Novorapid^® or Umuline rapide^® and infusion extension line materials (PVC, PE and coextruded (PE/PVC)). Insulin solution at 1 IU/mL was infused at 2 mL/h over 24 hours with 16 different extension lines (8 in PVC, 3 in PE and 5 in PE/PVC). Ultra-Fast Liquid Chromatography with diode array detection (UFLC-DAD) was performed to quantify insulin (human and aspart) and preservatives (metacresol and phenol). Limited human insulin sorption was observed thirty minutes after the onset of infusion: 24.3 ± 12.9%, 3.1 ± 1.6% and 18.6 ± 10.0% for PVC, PE and PE/PVC respectively. With insulin aspart, sorption of about 5% was observed at the onset of infusion for all materials. However, there were interactions between phenol and especially metacresol with PVC, but no interactions with PE and PE/PVC. This study shows that insulin interacts with PVC, PE and PE/PVC at the onset of infusion. It also demonstrates that insulin preservatives interact with PVC, which may result in problems of insulin conservation and conformation. Some more studies are required to understand the clinical impact of the latter during infusion.

Structure-based stabilization of insulin as a therapeutic protein assembly via enhanced aromatic-aromatic interactions

Key contributions to protein structure and stability are provided by weakly polar interactions, which arise from asymmetric electronic distributions within amino acids and peptide bonds. Of particular interest are aromatic side chains whose directional π-systems commonly stabilize protein interiors and interfaces. Here, we consider aromatic-aromatic interactions within a model protein assembly: the dimer interface of insulin. Semi-classical simulations of aromatic-aromatic interactions at this interface suggested that substitution of residue TyrB26 by Trp would preserve native structure while enhancing dimerization (and hence hexamer stability). The crystal structure of a [TrpB26]insulin analog (determined as a T3Rf3 zinc hexamer at a resolution of 2.25 Å) was observed to be essentially identical to that of WT insulin. Remarkably and yet in general accordance with theoretical expectations, spectroscopic studies demonstrated a 150-fold increase in the in vitro lifetime of the variant hexamer, a critical pharmacokinetic parameter influencing design of long-acting formulations. Functional studies in diabetic rats indeed revealed prolonged action following subcutaneous injection. The potency of the TrpB26-modified analog was equal to or greater than an unmodified control. Thus, exploiting a general quantum-chemical feature of protein structure and stability, our results exemplify a mechanism-based approach to the optimization of a therapeutic protein assembly.

Modeling Subcutaneous Absorption of Fast-Acting Insulin in Type 1 Diabetes

OBJECTIVE

Subcutaneous (sc) administration of fast-acting insulin analogues is the key in conventional therapy of type 1 diabetes (T1D). A model of sc insulin absorption would be helpful for optimizing insulin therapy and test new open- and closed-loop treatment strategies in in silico platforms. Some models have been published in the literature, but none was assessed on a frequently-sampled large dataset of T1D subjects. The aim here is to propose a model of sc absorption of fast-acting insulin, which is able to describe the data and precisely estimate model parameters with a clear physiological interpretation.

METHODS

Three candidate models were identified on 116 T1D subjects, who underwent a single sc injection of fast-acting insulin and were compared on the basis of their ability to describe the data and their numerical identifiability.

RESULTS

A linear two-compartment model including a subject-specific delay in sc insulin absorption is proposed. On average, a delay of 7.6 min in insulin appearance in the first compartment is detected, then the insulin is slowly absorbed into plasma (in 23% of the subjects) with a rate of 0.0034 min-1, while the remaining diffuses into the second compartment, with a rate constant of 0.028 min-1, and then finally absorbed into plasma with a rate constant of 0.014 min-1.

CONCLUSION

Among the three tested models, the one proposed here is the only one able to both accurately describe plasma insulin data after a single sc injection and precisely estimate physiologically plausible parameters. The model needs to be further tested in case of variable sc insulin delivery and/or multiple insulin doses.

SIGNIFICANCE

Results are expected to help the development of new open- and closed-loop insulin treatment strategies.

Rapid-Acting and Human Insulins: Hexamer Dissociation Kinetics upon Dilution of the Pharmaceutical Formulation

Purpose

Comparison of the dissociation kinetics of rapid-acting insulins lispro, aspart, glulisine and human insulin under physiologically relevant conditions.

Methods

Dissociation kinetics after dilution were monitored directly in terms of the average molecular mass using combined static and dynamic light scattering. Changes in tertiary structure were detected by near-UV circular dichroism.

Results

Glulisine forms compact hexamers in formulation even in the absence of Zn²⁺. Upon severe dilution, these rapidly dissociate into monomers in less than 10 s. In contrast, in formulations of lispro and aspart, the presence of Zn²⁺ and phenolic compounds is essential for formation of compact R6 hexamers. These slowly dissociate in times ranging from seconds to one hour depending on the concentration of phenolic additives. The disadvantage of the long dissociation times of lispro and aspart can be diminished by a rapid depletion of the concentration of phenolic additives independent of the insulin dilution. This is especially important in conditions similar to those after subcutaneous injection, where only minor dilution of the insulins occurs.

Conclusion

Knowledge of the diverging dissociation mechanisms of lispro and aspart compared to glulisine will be helpful for optimizing formulation conditions of rapid-acting insulins.

Electronic supplementary material

The online version of this article (doi:10.1007/s11095-017-2233-0) contains supplementary material, which is available to authorized users.

Insulin analogues in type 1 diabetes mellitus: getting better all the time

The treatment of type 1 diabetes mellitus consists of external replacement of the functions of β cells in an attempt to achieve blood levels of glucose as close to the normal range as possible. This approach means that glucose sensing needs to be replaced and levels of insulin need to mimic physiological insulin-action profiles, including basal coverage and changes around meals. Training and educating patients are crucial for the achievement of good glycaemic control, but having insulin preparations with action profiles that provide stable basal insulin coverage and appropriate mealtime insulin peaks helps people with type 1 diabetes mellitus to live active lives without sacrificing tight glycaemic control. Insulin analogues enable patients to achieve this goal, as some have fast action profiles, and some have very slow action profiles, which gives people with type 1 diabetes mellitus the tools to achieve dynamic insulin-action profiles that enable tight glycaemic control with a risk of hypoglycaemia that is lower than that with human short-acting and long-acting insulins. This Review discusses the established and novel insulin analogues that are used to treat patients with type 1 diabetes mellitus and provides insights into the future development of insulin analogues.

Improving drug-like properties of insulin and GLP-1 via molecule design and formulation and improving diabetes management with device & drug delivery

There is an increased incidence of diabetes worldwide. The discovery of insulin revolutionized the management of diabetes, the revelation of glucagon-like peptide-1 (GLP-1) and introduction of GLP-1 receptor agonists to clinical practice was another breakthrough. Continued translational research resulted in better understanding of diabetes, which, in combination with cutting-edge biology, chemistry, and pharmaceutical tools, have allowed for the development of safer, more effective and convenient insulins and GLP-1. Advances in self-administration of insulin and GLP-1 receptor agonist therapies with use of drug-device combination products have further improved the outcomes of diabetes management and quality of life for diabetic patients. The synergies of insulin and GLP-1 receptor agonist actions have led to development of devices that can deliver both molecules simultaneously. New chimeric GLP-1-incretins and insulin-GLP-1-incretin molecules are also being developed. The objective of this review is to summarize molecular designs to improve the drug-like properties of insulin and GLP-1 and to highlight the continued advancement of drug-device combination products to improve diabetes management.

Trehalose Glycopolymer Enhances Both Solution Stability and Pharmacokinetics of a Therapeutic Protein

Biocompatible polymers such as poly(ethylene glycol) (PEG) have been successfully conjugated to therapeutic proteins to enhance their pharmacokinetics. However, many of these polymers, including PEG, only improve the in vivo lifetimes and do not protect proteins against inactivation during storage and transportation. Herein, we report a polymer with trehalose side chains (PolyProtek) that is capable of improving both the external stability and the in vivo plasma half-life of a therapeutic protein. Insulin was employed as a model biologic, and high performance liquid chromatography and dynamic light scattering confirmed that addition of trehalose glycopolymer as an excipient or covalent conjugation prevented thermal or agitation-induced aggregation of insulin. The insulin-trehalose glycopolymer conjugate also showed significantly prolonged plasma circulation time in mice, similar to the analogous insulin-PEG conjugate. The insulin-trehalose glycopolymer conjugate was active as tested by insulin tolerance tests in mice and retained bioactivity even after exposure to high temperatures. The trehalose glycopolymer was shown to be nontoxic to mice up to at least 1.6 mg/kg dosage. These results together suggest that the trehalose glycopolymer should be further explored as an alternative to PEG for long circulating protein therapeutics.

Development of Insulin Detemir/Insulin Aspart Cross-Reacting Antibodies Following Treatment with Insulin Detemir: 104-week Study in Children and Adolescents with Type 1 Diabetes Aged 2-16 Years

BACKGROUND

To study the long-term development (104 weeks) of insulin antibodies during treatment with insulin detemir (IDet) and insulin aspart (IAsp) in children with type 1 diabetes aged 2-16 years.

METHODS

A 52-week, two-arm, randomized trial comparing IDet and neutral protamine Hagedorn insulin, both in combination with IAsp, was followed by a one-arm, 52-week extension trial of the IDet + IAsp arm. The present analysis was conducted in children who completed the randomized trial and entered into the extension trial.

RESULTS

Of the 177 children randomized to IDet treatment, 146 entered the extension trial. IDet-IAsp cross-reacting antibodies peaked within the first 39 weeks of treatment before gradually declining. A similar pattern was seen for IDet-specific and IAsp-specific antibodies. At end of trial (EOT), no correlation was observed between the level of IDet-specific or IAsp-specific antibodies or IDet-IAsp cross-reacting antibodies and either glycated hemoglobin (HbA1c) or basal insulin dose. Mean HbA1c was stable during the treatment period, with a slight increase over time from 8.41% (68.4 mmol/mol) at baseline to 8.74% (72 mmol/mol) at EOT. Mean IDet dose increased from 0.43 U/kg at baseline to 0.66 U/kg at EOT. Mean IAsp dose increased from 0.46 U/kg to 0.51 U/kg at EOT.

CONCLUSION

Although treatment with IDet and IAsp is associated with development of specific and cross-reacting antibodies, no correlation between insulin antibodies and basal insulin dose or HbA1c was found.

FUNDING

Novo Nordisk A/S. ClinicalTrials.gov identifiers: NCT00435019 and NCT00623194.

Insulin Aspart in the Management of Diabetes Mellitus: 15 Years of Clinical Experience

Limiting excessive postprandial glucose excursions is an important component of good overall glycemic control in diabetes mellitus. Pharmacokinetic studies have shown that insulin aspart, which is structurally identical to regular human insulin except for the replacement of a single proline amino acid with an aspartic acid residue, has a more physiologic time-action profile (i.e., reaches a higher peak and reaches that peak sooner) than regular human insulin. As expected with this improved pharmacokinetic profile, insulin aspart demonstrates a greater glucose-lowering effect compared with regular human insulin. Numerous randomized controlled trials and a meta-analysis have also demonstrated improved postprandial control with insulin aspart compared with regular human insulin in patients with type 1 or type 2 diabetes, as well as efficacy and safety in children, pregnant patients, hospitalized patients, and patients using continuous subcutaneous insulin infusion. Studies have demonstrated that step-wise addition of insulin aspart is a viable intensification option for patients with type 2 diabetes failing on basal insulin. Insulin aspart has shown a good safety profile, with no evidence of increased receptor binding, mitogenicity, stimulation of anti-insulin antibodies, or hypoglycemia compared with regular human insulin. In one meta-analysis, there was evidence of a lower rate of nocturnal hypoglycemia compared with regular human insulin and, in a trial that specifically included patients with a history of recurrent hypoglycemia, a significantly lower rate of severe hypoglycemic episodes. The next generation of insulin aspart (faster-acting insulin aspart) is being developed with a view to further improving on these pharmacokinetic/pharmacodynamic properties.

Review: Pharmacology of insulin

Diabetes is associated with microvascular and macrovascular complications leading to significant morbidity and mortality. Glycaemic control is important to prevent and delay the progression of these complications. An ideal insulin regimen in patients with diabetes would mirror the 24-hour insulin profile of a non-diabetic person and thereby prevent hyperglycaemia without inducing hypoglycaemia. This has, until recently, proved difficult to reproduce by regular subcutaneous insulin injections due to the inherent pharmacokinetic properties of the available insulins. Normoglycaemia was rarely achieved without hypoglycaemia compromising the quality of patients' lives. The advent of the new long- and short-acting insulin analogues are expected to both improve glycaemic control leading to a reduction in diabetes-related complications and reduce the incidence of hypoglycaemia thereby offering patients a better lifestyle.

Review: Insulin glulisine — the potential for improved glycaemic control

Tight glycaemic control is essential to reduce the risk of developing the micro- and macrovascular complications of diabetes. Plasma levels of glycosylated haemoglobin (HbA 1C) are a marker for long-term glycaemia; controlling these levels within tight limits forms the cornerstone of long-term diabetes management. As a result of evidence from key clinical trials in type 1 and type 2 diabetes, HbA1C targets ranging from < 6.5 to < 7.5% have been set by various authorities. To achieve these targets, insulin regimens need to reflect normal physiological insulin release. Several rapid- and long-acting insulin analogues have been developed to mimic aspects of insulin secretion. Insulin glulisine is a genetically engineered insulin which has a rapid onset and short lived action, allowing it to closely mimic prandial release of insulin. In addition to the structural change in the insulin molecule, the absence of excess zinc and the addition of polysorbate 20 as a surfactant facilitates its disassociation in the subcutaneous tissue and inhibits its aggregation when used in subcutaneous insulin delivery systems due to improved physical stability.

Interaction of insulin with methyl tert-butyl ether promotes molten globule-like state and production of reactive oxygen species

Interaction of methyl tert-butyl ether (MTBE) with proteins is a new look at its potential adverse biological effects. When MTBE is released to the environment it enters the blood stream through inhalation, and could affect the properties of various proteins. Here we investigated the interaction of MTBE with insulin and its effect on insulin structural changes. Our results showed that insulin formed a molten globule (MG)-like structure in the presence of 8 μM MTBE under physiological pH. The insulin structural changes were studied using spectroscopy methods, viscosity calculation, dynamic light scattering and differential scanning calorimetry. To delineate the mechanisms involved in MTBE-protein interactions, the formation of reactive oxygen specious (ROS) and formation of protein aggregates were measured. The chemiluminscence experiments revealed an increase in ROS production in the presence of MTBE especially in the MG-like state. These results were further confirmed by the aggregation tests, which indicated more aggregation of insulin at 40 μM MTBE compared with 8 μM. Thus, the formation of initial aggregates and exposure of the hydrophobic patches upon formation of the MG-like state in the presence of MTBE drives protein oxidation and ROS generation.

Low molecular weight chitosan-insulin polyelectrolyte complex: characterization and stability studies

The aim of the work reported herein was to investigate the effect of various low molecular weight chitosans (LMWCs) on the stability of insulin using USP HPLC methods. Insulin was found to be stable in a polyelectrolyte complex (PEC) consisting of insulin and LMWC in the presence of a Tris-buffer at pH 6.5. In the presence of LMWC, the stability of insulin increased with decreasing molecular weight of LMWC; 13 kDa LMWC was the most efficient molecular weight for enhancing the physical and chemical stability of insulin. Solubilization of insulin-LMWC polyelectrolyte complex (I-LMWC PEC) in a reverse micelle (RM) system, administered to diabetic rats, results in an oral delivery system for insulin with acceptable bioactivity.

Central nervous insulin administration does not potentiate the acute glucoregulatory impact of concurrent mild hyperinsulinemia

Experiments in rodents suggest that hypothalamic insulin signaling essentially contributes to the acute control of peripheral glucose homeostasis. Against this background, we investigated in healthy humans whether intranasal (IN) insulin, which is known to effectively reach the brain compartment, impacts systemic glucose metabolism. Twenty overnight-fasted healthy, normal-weight men were IN administered 210 and 420 international units [IU] (10 and 20 IU every 15 min) of the insulin analog aspart (ins-asp) and placebo, respectively, during experimental sessions lasting 6 h. The use of ins-asp rather than human insulin enabled us to disentangle exogenous and endogenous insulin kinetics. IN insulin dose-dependently decreased plasma glucose concentrations while reducing C-peptide and attenuating endogenous insulin levels. However, we also observed a slight dose-dependent permeation of ins-asp into the circulation. In control experiments mimicking the systemic but not the central nervous uptake of the IN 210 IU dose via intravenous infusion of ins-asp at a dose of 0.12 IU/kg/24 h (n = 10), we obtained essentially identical effects on fasting plasma glucose concentrations. This pattern indicates that sustained IN insulin administration to the human brain to enhance central nervous insulin signaling does not acutely alter systemic glucose homeostasis beyond effects accounted for by concurrent mild hyperinsulinemia.