Insulin analogs with improved pharmacokinetic profiles

Improving the stability of insulin through effective chemical modifications: A Comprehensive review

Insulin, an essential peptide hormone, conjointly regulates blood glucose levels by its receptor and it is used as vital drug to treat diabetes. This therapeutic hormone may undergo different chemical modifications during industrial processes, pharmaceutical formulation, and through its endogenous storage in the pancreatic β-cells. Insulin is highly sensitive to environmental stresses and readily undergoes structural changes, being also able to unfold and aggregate in physiological conditions. Even; small changes altering the structural integrity of insulin may have significant impacts on its biological efficacy to its physiological and pharmacological activities. Insulin analogs have been engineered to achieve modified properties, such as improved stability, solubility, and pharmacokinetics, while preserving the molecular pharmacology of insulin. The casually or purposively strategies of chemical modifications of insulin occurred to improve its therapeutic and pharmaceutical properties. Knowing the effects of chemical modification, formation of aggregates, and nanoparticles on protein can be a new look at the production of protein analogues drugs and its application in living system. The project focused on effects of chemical modifications and nanoparticles on the structure, stability, aggregation and their results in effective drug delivery system, biological activity, and pharmacological properties of insulin. The future challenge in biotechnology and pharmacokinetic arises from the complexity of biopharmaceuticals, which are often molecular structures that require formulation and delivery strategies to ensure their efficacy and safety.

Understanding the Reversible Binding of a Multichain Protein-Protein Complex through Free-Energy Calculations

We demonstrate that the binding affinity of a multichain protein-protein complex, insulin dimer, can be accurately predicted using a streamlined route of standard binding free-energy calculations. We find that chains A and C, which do not interact directly during binding, stabilize the insulin monomer structures and reduce the binding affinity of the two monomers, therefore enabling their reversible association. Notably, we confirm that although classical methods can estimate the binding affinity of the insulin dimer, conventional molecular dynamics, enhanced sampling algorithms, and classical geometrical routes of binding free-energy calculations may not fully capture certain aspects of the role played by the noninteracting chains in the binding dynamics. Therefore, this study not only elucidates the role of noninteracting chains in the reversible binding of the insulin dimer but also offers a methodological guide for investigating the reversible binding of multichain protein-protein complexes utilizing streamlined free-energy calculations.

Exploring the Higher Order Structure and Conformational Transitions in Insulin Microcrystalline Biopharmaceuticals by Proton-Detected Solid-State Nuclear Magnetic Resonance at Natural Abundance

The integrity of a higher order structure (HOS) is an essential requirement to ensure the efficacy, stability, and safety of protein therapeutics. Solution-state nuclear magnetic resonance (NMR) occupies a unique niche as one of the most promising methods to access atomic-level structural information on soluble biopharmaceutical formulations. Another major class of drugs is poorly soluble, such as microcrystalline suspensions, which poses significant challenges for the characterization of the active ingredient in its native state. Here, we have demonstrated a solid-state NMR method for HOS characterization of biopharmaceutical suspensions employing a selective excitation scheme under fast magic angle spinning (MAS). The applicability of the method is shown on commercial insulin suspensions at natural isotopic abundance. Selective excitation aided with proton detection and non-uniform sampling (NUS) provides improved sensitivity and resolution. The enhanced resolution enabled us to demonstrate the first experimental evidence of a phenol-escaping pathway in insulin, leading to conformational transitions to different hexameric states. This approach has the potential to serve as a valuable means for meticulously examining microcrystalline biopharmaceutical suspensions, which was previously not attainable in their native formulation states and can be seamlessly extended to other classes of biopharmaceuticals such as mAbs and other microcrystalline proteins.

Polymorphic nanobody crystals as long-acting intravitreal therapy for wet age-related macular degeneration

Wet age-related macular degeneration (wet AMD) is the most common cause of blindness, and chronic intravitreal injection of anti-vascular endothelial growth factor (VEGF) proteins has been the dominant therapeutic approach. Less intravitreal injection and a prolonged inter-injection interval are the main drivers behind new wet AMD drug innovations. By rationally engineering the surface residues of a model anti-VEGF nanobody, we obtained a series of anti-VEGF nanobodies with identical protein structures and VEGF binding affinities, while drastically different crystallization propensities and crystal lattice structures. Among these nanobody crystals, the P212121 lattice appeared to be denser and released protein slower than the P1 lattice, while nanobody crystals embedding zinc coordination further slowed the protein release rate. The polymorphic protein crystals could be a potentially breakthrough strategy for chronic intravitreal administration of anti-VEGF proteins.

Combined Liquid-State and Solid-State Nuclear Magnetic Resonance at Natural Abundance for Comparative Higher Order Structure Assessment in the Formulated-State of Biphasic Biopharmaceutics

A higher-order structure (HOS) is critical to a biopharmaceutical drug as the three-dimensional structure governs its function. Even the partial perturbation in the HOS of the drug can alter the biological efficiency and efficacy. Due to current limitations in analytical technologies, it is imperative to develop a protocol to characterize the HOS of biopharmaceuticals in the native formulated state. This becomes even more challenging for the suspension formulations where solution and solid phases co-exist. Here, we have used a combinatorial approach using liquid (1D ¹H) and solid-state (¹³C CP MAS) NMR methodology to demonstrate the HOS in the biphasic microcrystalline suspension drug in its formulated state. The data were further assessed by principal component analysis and Mahalanobis distance (D_M) calculation for quantitative assessment. This approach is sufficient to provide information regarding the protein HOS and the local dynamics of the molecule when combined with orthogonal techniques such as X-ray scattering. Our method can be an elegant tool to investigate batch-to-batch variation in the process of manufacture and storage as well as a biosimilarity comparison study for biphasic/microcrystalline suspension.

Amyloid Fibrillation of Insulin: Amelioration Strategies and Implications for Translation

Insulin is a therapeutically relevant molecule with use in treating diabetes patients. Unfortunately, it undergoes a range of untoward and often unpredictable physical transformations due to alterations in its biochemical environment, including pH, ionic strength, temperature, agitation, and exposure to hydrophobic surfaces. The transformations are prevalent in its physiologically active monomeric form, while the zinc cation-coordinated hexamer, although physiologically inactive, is stable and less susceptible to fibrillation. The resultant molecular reconfiguration, including unfolding, misfolding, and hydrophobic interactions, often results in agglomeration, amyloid fibrillogenesis, and precipitation. As a result, a part of the dose is lost, causing a compromised therapeutic efficacy. Besides, the amyloid fibrils form insoluble deposits, trigger immunologic reactions, and harbor cytotoxic potential. The physical transformations also hold back a successful translation of non-parenteral insulin formulations, in addition to challenges related to encapsulation, chemical modification, purification, storage, and dosing. This review revisits the mechanisms and challenges that drive such physical transformations in insulin, with an emphasis on the observed amyloid fibrillation, and presents a critique of the current amelioration strategies before prioritizing some future research objectives.

Macromolecular protein crystallisation with biotemplate of live cells

Macromolecular protein crystallisation was one of the potential tools to accelerate the biomanufacturing of biopharmaceuticals. In this work, it was the first time to investigate the roles of biotemplates, Saccharomyces cerevisiae live cells, in the crystallisation processes of lysozyme, with different concentrations from 20 to 2.5 mg/mL lysozyme and different concentrations from 0 to 5.0 × 10⁷ (cfu/mL) Saccharomyces cerevisiae cells, during a period of 96 h. During the crystallisation period, the nucleation possibility in droplets, crystal numbers, and cell growth and cell density were observed and analysed. The results indicated the strong interaction between the lysozyme molecules and the cell wall of the S. cerevisiae, proved by the crystallization of lysozyme with fluorescent labels. The biotemplates demonstrated positive influence or negative influence on the nucleation, i.e. shorter or longer induction time, dependent on the concentrations of the lysozyme and the S. cerevisiae cells, and ratios between them. In the biomanufacturing process, target proteins were various cells were commonly mixed with various cells, and this work provides novel insights of new design and application of live cells as biotemplates for purification of macromolecules.

Investigating Crystalline Protein Suspension Formulations of Pembrolizumab from MAS NMR Spectroscopy

Developing biological formulations to maintain the chemical and structural integrity of therapeutic antibodies remains a significant challenge. Monoclonal antibody (mAb) crystalline suspension formulation is a promising alternative for high concentration subcutaneous drug delivery. It demonstrates many merits compared to the solution formulation to reach a high concentration at the reduced viscosity and enhanced stability. One main challenge in drug development is the lack of high-resolution characterization of the crystallinity and stability of mAb microcrystals in the native formulations. Conventional analytical techniques often cannot evaluate structural details of mAb microcrystals in the native suspension due to the presence of visible particles, relatively small crystal size, high protein concentration, and multicomponent nature of a liquid formulation. This study demonstrates the first high-resolution characterization of mAb microcrystalline suspension using magic angle spinning (MAS) NMR spectroscopy. Crystalline suspension formulation of pembrolizumab (Keytruda, Merck & Co., Inc., Kenilworth, NJ 07033, U.S.) is utilized as a model system. Remarkably narrow ¹³C spectral linewidth of approximately 29 Hz suggests a high order of crystallinity and conformational homogeneity of pembrolizumab crystals. The impact of thermal stress and dehydration on the structure, dynamics, and stability of these mAb crystals in the formulation environment is evaluated. Moreover, isotopic labeling and heteronuclear ¹³C and ¹⁵N spectroscopies have been utilized to identify the binding of caffeine in the pembrolizumab crystal lattice, providing molecular insights into the cocrystallization of the protein and ligand. Our study provides valuable structural details for facilitating the design of crystalline suspension formulation of Keytruda and demonstrates the high potential of MAS NMR as an advanced tool for biophysical characterization of biological therapeutics.

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.

Transfer of a Rational Crystal Contact Engineering Strategy between Diverse Alcohol Dehydrogenases

Protein crystallization can serve as a purification step in biotechnological processes but is often limited by the non-crystallizability of proteins. Enabling or improving crystallization is mostly achieved by high-throughput screening of crystallization conditions and, more recently, by rational crystal contact engineering. Two selected rational crystal contact mutations, Q126K and T102E, were transferred from the alcohol dehydrogenases of Lactobacillus brevis (LbADH) to Lactobacillus kefir (LkADH). Proteins were expressed in E. coli and batch protein crystallization was performed in stirred crystallizers. Highly similar crystal packing of LkADH wild type compared to LbADH, which is necessary for the transfer of crystal contact engineering strategies, was achieved by aligning purification tag and crystallization conditions, as shown by X-ray diffraction. After comparing the crystal sizes after crystallization of LkADH mutants with the wild type, the mean protein crystal size of LkADH mutants was reduced by 40–70% in length with a concomitant increase in the total amount of crystals (higher number of nucleation events). Applying this measure to the LkADH variants studied results in an order of crystallizability T102E > Q126K > LkADH wild type, which corresponds to the results with LbADH mutants and shows, for the first time, the successful transfer of crystal contact engineering strategies.

THE MAKING OF A FOOTPRINT IN PROTEIN FOOTPRINTING: A REVIEW IN HONOR OF MICHAEL L. GROSS

Within the past decade protein footprinting in conjunction with mass spectrometry has become a powerful and versatile means to unravel the higher order structure of proteins. Footprinting-based approaches has demonstrated the capacity to inform on interaction sites and dynamic regions that participate in conformational changes. These findings when set in a biological perspective inform on protein folding/unfolding, protein-protein interactions, and protein-ligand interactions. In this review, we will look at the contribution of Dr. Michael L. Gross to protein footprinting approaches such as hydrogen deuterium exchange mass spectrometry and hydroxyl radical protein footprinting. This review details the development of novel footprinting methods as well as their applications to study higher order protein structure. © 2020 The Authors. Mass Spectrometry Reviews published by John Wiley & Sons Ltd. Mass Spec Rev.

Calculating the absolute binding free energy of the insulin dimer in an explicit solvent

Insulin is a significant hormone in the regulation of glucose level in the blood. Its monomers bind to each other to form dimers or hexamers through a complex process. To study the binding of the insulin dimer, we first calculate its absolute binding free energy by the steered molecular dynamics method and the confinement method based on a fictitious thermodynamic cycle. After considering some special correction terms, the final calculated binding free energy at 298 K is −8.97 ± 1.41 kcal mol⁻¹, which is close to the experimental value of −7.2 ± 0.8 kcal mol⁻¹. Furthermore, we discuss the important residue–residue interactions between the insulin monomers, including hydrophobic interactions, π–π interactions and hydrogen bond interactions. The analysis reveals five key residues, Vla^B12, Tyr^B16, Phe^B24, Phe^B25, and Tyr^B26, for the dimerization of the insulin. We also perform MM-PBSA calculations for the wild-type dimer and some mutants and study the roles of the key residues by the change of the binding energy of the insulin dimer.

In this paper, we calculate the absolute binding free energy of an insulin dimer by steered MD method. The result of −8.97 kcal mol⁻¹ is close to the experimental value −7.2 kcal mol⁻¹. We also analyze the residue–residue interactions.

Physical PEGylation to Prevent Insulin Fibrillation

Insulin is one of the most marketed therapeutic proteins worldwide. However, its formulation suffers from fibrillation, which affects the long-term storage limiting the development of novel devices for sustained delivery including portable infusion devices. We have investigated the effect of physical PEGylation on structural and colloidal stability of insulin by using 2 PEGylating agents terminating with polycyclic hydrophobic moieties, cholane and cholesterol: mPEG_5kDa-cholane and mPEG_5kDa-cholesterol, respectively. Microcalorimetric analyses showed that mPEG_5kDa-cholane and mPEG_5kDa-cholesterol efficiently bind insulin with binding constants (Ka) of 3.98 10⁴ and 1.14 10⁵ M^-1, respectively. At room temperature, the 2 PEGylating agents yielded comparable structural stabilization of α-helix conformation and decreased dimerization of insulin. However, melting studies showed that mPEG_5kDa-cholesterol has superior stabilizing effect of the protein conformation than mPEG_5kDa-cholane. Furthermore, the fibrillation study showed that at a 1:1 and 1:5 insulin/polymer molar ratios, mPEG_5kDa-cholesterol delays insulin fibrillation 40% and 26% more efficiently, respectively, as compared to mPEG_5kDa-cholane which was confirmed by transmission electron microscopy imaging. Insulin was released from the mPEG_5kDa-cholane and mPEG_5kDa-cholesterol assemblies with comparable kinetic profiles. The physical PEGylation has a beneficial effect on the stabilization and shielding of the insulin structure into the monomeric form, which is not prone to fibrillation and aggregation.

Outcomes and clinical implications of intranasal insulin administration to the central nervous system

Insulin signaling in the brain plays a critical role in metabolic control and cognitive function. Targeting insulinergic pathways in the central nervous system via peripheral insulin administration is feasible, but associated with systemic effects that necessitate tight supervision or countermeasures. The intranasal route of insulin administration, which largely bypasses the circulation and thereby greatly reduces these obstacles, has now been repeatedly tested in proof-of-concept studies in humans as well as animals. It is routinely used in experimental settings to investigate the impact on eating behavior, peripheral metabolism, memory function and brain activation of acute or long-term enhancements in central nervous system insulin signaling. Epidemiological and experimental evidence linking deteriorations in metabolic control such as diabetes with neurodegenerative diseases imply pathophysiological relevance of dysfunctional brain insulin signaling or brain insulin resistance, and suggest that targeting insulin in the brain holds some promise as a therapy or adjunct therapy. This short narrative review gives an overview over recent findings on brain insulin signaling as derived from human studies deploying intranasal insulin, and evaluates the potential of therapeutic interventions that target brain insulin resistance.

Elucidating the Mechanism of Absorption of Fast-Acting Insulin Aspart: The Role of Niacinamide

Purpose

Fast-acting insulin aspart (faster aspart) is a novel formulation of insulin aspart containing two additional excipients: niacinamide, to increase early absorption, and L-arginine, to optimize stability. The aim of this study was to evaluate the impact of niacinamide on insulin aspart absorption and to investigate the mechanism of action underlying the accelerated absorption.

Methods

The impact of niacinamide was assessed in pharmacokinetic analyses in pigs and humans, small angle X-ray scattering experiments, trans-endothelial transport assays, vascular tension measurements, and subcutaneous blood flow imaging.

Results

Niacinamide increased the rate of early insulin aspart absorption in pigs, and pharmacokinetic modelling revealed this effect to be most pronounced up to ~30–40 min after injection in humans. Niacinamide increased the relative monomer fraction of insulin aspart by ~35%, and the apparent permeability of insulin aspart across an endothelial cell barrier by ~27%. Niacinamide also induced a concentration-dependent vasorelaxation of porcine arteries, and increased skin perfusion in pigs.

Conclusion

Niacinamide mediates the acceleration of initial insulin aspart absorption, and the mechanism of action appears to be multifaceted. Niacinamide increases the initial abundance of insulin aspart monomers and transport of insulin aspart after subcutaneous administration, and also mediates a transient, local vasodilatory effect.

Electronic supplementary material

The online version of this article (10.1007/s11095-019-2578-7) contains supplementary material, which is available to authorized users.

Stabilizing proteins to prevent conformational changes required for amyloid fibril formation

Amyloid fibrillation is associated with several human maladies, such as Alzheimer's, Parkinson's, Huntington's diseases, prions, amyotrophic lateral sclerosis, and type 2 diabetes diseases. Gaining insights into the mechanism of amyloid fibril formation and exploring novel approaches to fibrillation inhibition are crucial for preventing amyloid diseases. Here, we hypothesized that ligands capable of stabilizing the native state of query proteins might prevent protein unfolding, which, in turn, may reduce the propensity of proteins to form amyloid fibrils. We demonstrated the efficient inhibition of amyloid formation of the human serum albumin (HSA) (up to 85%) and human insulin (up to 80%) by a nonsteroidal anti-inflammatory drug, ibuprofen (IBFN). IBFN significantly increases the conformational stability of both HSA and insulin, as confirmed by differential scanning calorimetry (DSC). Moreover, increasing concentration of IBFN boosts its amyloid inhibitory propensity in a linear fashion by influencing the nucleation phase as assayed by thioflavin T fluorescence, transmission electron microscopy, and dynamic light scattering. Furthermore, circular dichroism analysis supported the DSC results, showing that IBFN binds to the native state of proteins and almost completely prevents their tendency to lose secondary and tertiary structures. Cell toxicity assay confirms that species formed in the presence of IBFN are less toxic to neuronal cells (SH-SY5Y). These results demonstrate the feasibility of using a small molecule to stabilize the native state of proteins, thereby preventing the amyloidogenic conformational changes, which appear to be the common link in several human amyloid diseases.

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.

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.

Scope and Limitations of Fmoc Chemistry SPPS-Based Approaches to the Total Synthesis of Insulin Lispro via Ester Insulin

We have systematically explored three approaches based on 9-fluorenylmethoxycarbonyl (Fmoc) chemistry solid phase peptide synthesis (SPPS) for the total chemical synthesis of the key depsipeptide intermediate for the efficient total chemical synthesis of insulin. The approaches used were: stepwise Fmoc chemistry SPPS; the "hybrid method", in which maximally protected peptide segments made by Fmoc chemistry SPPS are condensed in solution; and, native chemical ligation using peptide-thioester segments generated by Fmoc chemistry SPPS. A key building block in all three approaches was a Glu[O-β-(Thr)] ester-linked dipeptide equipped with a set of orthogonal protecting groups compatible with Fmoc chemistry SPPS. The most effective method for the preparation of the 51 residue ester-linked polypeptide chain of ester insulin was the use of unprotected peptide-thioester segments, prepared from peptide-hydrazides synthesized by Fmoc chemistry SPPS, and condensed by native chemical ligation. High-resolution X-ray crystallography confirmed the disulfide pairings and three-dimensional structure of synthetic insulin lispro prepared from ester insulin lispro by this route. Further optimization of these pilot studies could yield an efficient total chemical synthesis of insulin lispro (Humalog) based on peptide synthesis by Fmoc chemistry SPPS.

Structural Perspectives of Insulin Receptor Isoform-Selective Insulin Analogs

A significant drawback of the exogenous administration of insulin to diabetics is the non-physiological profile of insulin action resulting in the insufficient suppression of hepatic glucose production, which is the main contributing factor to diabetic hyperglycemia under fasting conditions and the basis of the challenge to restore a more physiological glucose profile in diabetes. The insulin receptor (IR) exists in two alternatively spliced variants, IR-A and IR-B, with different tissue distribution. While peripheral tissues contain different proportions of both isoforms, hepatic cells almost exclusively contain IR-B. In this respect, IR-B-selective insulin analogs would be of great interest for their potential to restore more natural metabolic homeostasis in diabetes. Recent advances in the structural biology of insulin and IR have provided new clues for understanding the interaction of both proteins. This article discusses and offers some structural perspectives for the design of specific insulin analogs with a preferential binding to IR-B.

Insulin Formulation Characterization-the Thioflavin T Assays

The insulin molecule was discovered in 1921. Shortly thereafter, its propensity towards amyloid fibril formation, fibrillation, was observed and described in the literature as a "precipitate." In the past decades, the increased incidence of type 2 diabetes has reached global epidemic proportions. This has emphasized the demands for both insulin production and the development of modern insulin products for unmet medical needs. Bringing such new insulin drug products to the market for the benefit of patients requires that many CMC-related processes are understood, described, and controlled. One potential undesired process is insulin fibril formation. The compound thioflavin T (ThT) is known as a fluorescent probe for amyloid fibrils. As such, ThT is utilized in a versatile research assay in microtiter plate format, the ThT assay. This review will describe an experimental set-up using not only a ThT microtiter plate assay but also two orthogonal methods. The use of the ThT assay in research and characterization of insulin analogues, as well as formulations of insulin, is described by cases drawn from the scientific literature and patents. The ThT assay is compared to other physical stability tests and in conclusion the advantages and limitations of the assay are compared.

Brain Insulin Resistance at the Crossroads of Metabolic and Cognitive Disorders in Humans

Ever since the brain was identified as an insulin-sensitive organ, evidence has rapidly accumulated that insulin action in the brain produces multiple behavioral and metabolic effects, influencing eating behavior, peripheral metabolism, and cognition. Disturbances in brain insulin action can be observed in obesity and type 2 diabetes (T2D), as well as in aging and dementia. Decreases in insulin sensitivity of central nervous pathways, i.e., brain insulin resistance, may therefore constitute a joint pathological feature of metabolic and cognitive dysfunctions. Modern neuroimaging methods have provided new means of probing brain insulin action, revealing the influence of insulin on both global and regional brain function. In this review, we highlight recent findings on brain insulin action in humans and its impact on metabolism and cognition. Furthermore, we elaborate on the most prominent factors associated with brain insulin resistance, i.e., obesity, T2D, genes, maternal metabolism, normal aging, inflammation, and dementia, and on their roles regarding causes and consequences of brain insulin resistance. We also describe the beneficial effects of enhanced brain insulin signaling on human eating behavior and cognition and discuss potential applications in the treatment of metabolic and cognitive disorders.

Biphasic insulin Aspart 30 vs. NPH plus regular human insulin in type 2 diabetes patients; a cost-effectiveness study

BACKGROUND

The aim of this study was to compare the efficacy, safety, costs, and cost-effectiveness of biphasic insulin aspart 30 (BIAsp 30) with NPH plus regular human insulin (NPH/Reg) in patients with type 2 diabetes mellitus (T2DM).

METHODS

It was a Single-center, parallel-group, randomized, clinical trial (Trial Registration: NCT01889095). One hundred and seventy four T2DM patients with poorly controlled diabetes (HbA1c ≥ 8 % (63.9 mmol/mol)) were randomly assigned to trial arms (BIAsp 30 and NPH/Reg) and were followed up for 48 weeks. BIAsp 30 was started at an initial dose of 0.2-0.6 IU/Kg in two divided doses and was titrated according to the glycemic status of the patient. Similarly, NPH/Reg insulin was initiated at a dose of 0.2-0.6 IU/Kg with a 2:1 ratio and was subsequently titrated. Level of glycemic control, hypoglycemic events, direct and indirect costs, quality adjusted life year (QALY) and incremental cost-effectiveness ratio have been assessed.

RESULTS

HbA1c, Fasting plasma glucose (FPG), and two-hour post-prandial glucose (PPG) were improved in both groups during the study (P < 0.05 for all analyses). Lower frequencies of minor, major, and nocturnal hypoglycemic episodes were observed with BIAsp 30 (P < 0.05). Additionally, BIAsp 30 was associated with less weight gain and also higher QALYs (P < 0.05). Total medical and non-medical costs were significantly lower with BIAsp 30 as compared with NPH/Reg (930.55 ± 81.43 USD vs. 1101.24 ± 165.49 USD, P = 0.004). Moreover, BIAsp 30 showed lower ICER as a dominant alternative.

CONCLUSIONS

Despite being more expensive, BIAsp 30 offers the same glycemic control as to NPH/Reg dose-dependently and also appears to cause fewer hypoglycemic events and to be more cost-effective in Iranian patients with type 2 diabetes.

Manipulation of lysozyme phase behavior by additives as function of conformational stability

Undesired protein aggregation in general and non-native protein aggregation in particular need to be inhibited during bio-pharmaceutical processing to ensure patient safety and to maintain product activity. In this work the potency of different additives, namely glycerol, PEG 1000, and glycine, to prevent lysozyme aggregation and selectively manipulate lysozyme phase behavior was investigated. The results revealed a strong pH dependency of the additive impact on lysozyme phase behavior, lysozyme solubility, crystal size and morphology. This work aims to link this pH dependent impact to a protein-specific parameter, the conformational stability of lysozyme. At pH 3 the addition of 10% (w/v) glycerol, 10% (w/v) PEG 1000, and 1 M glycine stabilized or destabilized lysozymes' native conformation resulting in a modified size of the crystallization area without influencing lysozyme solubility, crystal size and morphology. Addition of 1 M glycine even promoted non-native aggregation at pH 3 whereas addition of PEG 1000 completely inhibited non-native aggregation. At pH 5 the addition of 10% (w/v) glycerol, 10% (w/v) PEG 1000, and 1 M glycine did not influence lysozymes' native conformation, but strongly influenced the position of the crystallization area, lysozyme solubility, crystal size and morphology. The observed pH dependent impact of the additives could be linked to a differing lysozyme conformational stability in the binary systems without additives at pH 3 and pH 5. However, in any case lysozyme phase behavior could selectively be manipulated by addition of glycerol, PEG 1000 and glycine. Furthermore, at pH 5 crystal size and morphology could selectively be manipulated.

Effects of phenol and meta-cresol depletion on insulin analog stability at physiological temperature

The stability of three commercial "fast-acting" insulin analogs, insulin lispro, insulin aspart, and insulin glulisine, was studied at various concentrations of phenolic preservatives (phenol and/or meta-cresol) during 9 days of incubation at 37 °C. The analysis by both size-exclusion and reversed-phase chromatography showed degradation of lispro and aspart that was inversely dependent on the concentration of phenolic preservatives. Insulin glulisine was much more stable than the other analogs and showed minimal degradation even in the absence of phenolic preservatives. With sedimentation velocity ultracentrifugation, we determined the preservatives' effect on the insulins' self-assembly. When depleted of preservatives, insulin glulisine dissociates from higher molecular weight species into a number of intermediate molecular weight species, in between monomer and hexamer, whereas insulin aspart and insulin lispro dissociate into monomers and dimers. Decreased stability of insulin lispro and insulin aspart seems to be because of the extent of dissociation when depleted of preservative. Insulin glulisine's dissociation to intermediate molecular weight species appears to help minimize its degradation during incubation at 37 °C.

Present status of insulin therapy for type 2 diabetes treated by general practitioners and diabetes specialists in Japan: Third report of a cross-sectional survey of 15,652 patients

Aims/Introduction:  Insulin therapy is often required to achieve good glycemic control in patients with type 2 diabetes mellitus. However, some providers, particularly general practitioners (GPs), are reluctant to prescribe insulin to their patients. The aim of the present study was to clarify any differences in, as well as any problems associated with, insulin therapy in patients with type 2 diabetes being treated by either a GP or a diabetes specialist in Japan.

Materials and Methods:  Of 15,652 patients across 721 clinics and hospitals, 15,350 were diagnosed with type 2 diabetes (14,312 by GPs and 1038 by specialists). Data regarding glycated hemoglobin (HbA_1c) levels, age, height, bodyweight and treatment modality were collected for each patient.

Results:  Of the patients with type 2 diabetes, 9.1 and 22.9% had been prescribed insulin monotherapy, and 38.8 and 37.0% were also receiving insulin with an oral antidiabetic (OAD) by GPs or specialists, respectively. Diabetes specialists prescribed analog insulin more frequently than did GPs. GPs chose premixed insulin more frequently than did specialists, and this factor correlated with higher HbA_1c levels. A younger age and daily insulin dose in groups being treated by both providers were correlated with high HbA_1c levels on insulin monotherapy. Neither type of insulin nor OAD was correlated with HbA_1c on insulin plus OAD therapy.

Conclusions:  To achieve better glycemic control with insulin therapy, sufficient insulin dose and intensive treatment regimen, in addition to lifestyle interventions, might be necessary. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2012.00198.x, 2012)

Near-infrared-actuated devices for remotely controlled drug delivery

A reservoir that could be remotely triggered to release a drug would enable the patient or physician to achieve on-demand, reproducible, repeated, and tunable dosing. Such a device would allow precise adjustment of dosage to desired effect, with a consequent minimization of toxicity, and could obviate repeated drug administrations or device implantations, enhancing patient compliance. It should exhibit low off-state leakage to minimize basal effects, and tunable on-state release profiles that could be adjusted from pulsatile to sustained in real time. Despite the clear clinical need for a device that meets these criteria, none has been reported to date to our knowledge. To address this deficiency, we developed an implantable reservoir capped by a nanocomposite membrane whose permeability was modulated by irradiation with a near-infrared laser. Irradiated devices could exhibit sustained on-state drug release for at least 3 h, and could reproducibly deliver short pulses over at least 10 cycles, with an on/off ratio of 30. Devices containing aspart, a fast-acting insulin analog, could achieve glycemic control after s.c. implantation in diabetic rats, with reproducible dosing controlled by the intensity and timing of irradiation over a 2-wk period. These devices can be loaded with a wide range of drug types, and therefore represent a platform technology that might be used to address a wide variety of clinical indications.

Pharmacokinetics, pharmacodynamics and physiologically-based pharmacokinetic modelling of monoclonal antibodies

Development of monoclonal antibodies (mAbs) and their functional derivatives represents a growing segment of the development pipeline in the pharmaceutical industry. More than 25 mAbs and derivatives have been approved for a variety of therapeutic applications. In addition, around 500 mAbs and derivatives are currently in different stages of development. mAbs are considered to be large molecule therapeutics (in general, they are 2-3 orders of magnitude larger than small chemical molecule therapeutics), but they are not just big chemicals. These compounds demonstrate much more complex pharmacokinetic and pharmacodynamic behaviour than small molecules. Because of their large size and relatively poor membrane permeability and instability in the conditions of the gastrointestinal tract, parenteral administration is the most usual route of administration. The rate and extent of mAb distribution is very slow and depends on extravasation in tissue, distribution within the particular tissue, and degradation. Elimination primarily happens via catabolism to peptides and amino acids. Although not definitive, work has been published to define the human tissues mainly involved in the elimination of mAbs, and it seems that many cells throughout the body are involved. mAbs can be targeted against many soluble or membrane-bound targets, thus these compounds may act by a variety of mechanisms to achieve their pharmacological effect. mAbs targeting soluble antigen generally exhibit linear elimination, whereas those targeting membrane-bound antigen often exhibit non-linear elimination, mainly due to target-mediated drug disposition (TMDD). The high-affinity interaction of mAbs and their derivatives with the pharmacological target can often result in non-linear pharmacokinetics. Because of species differences (particularly due to differences in target affinity and abundance) in the pharmacokinetics and pharmacodynamics of mAbs, pharmacokinetic/pharmacodynamic modelling of mAbs has been used routinely to expedite the development of mAbs and their derivatives and has been utilized to help in the selection of appropriate dose regimens. Although modelling approaches have helped to explain variability in both pharmacokinetic and pharmacodynamic properties of these drugs, there is a clear need for more complex models to improve understanding of pharmacokinetic processes and pharmacodynamic interactions of mAbs with the immune system. There are different approaches applied to physiologically based pharmacokinetic (PBPK) modelling of mAbs and important differences between the models developed. Some key additional features that need to be accounted for in PBPK models of mAbs are neonatal Fc receptor (FcRn; an important salvage mechanism for antibodies) binding, TMDD and lymph flow. Several models have been described incorporating some or all of these features and the use of PBPK models are expected to expand over the next few years.

Structural polymorphism and possible pathways of amyloid fibril formation on the example of insulin protein

In this review we analyze the main works on amyloid formation of insulin. There are many environmental factors affecting the formation of insulin amyloid fibrils (and other amyloidogenic proteins) such as: protein concentration, pH, ionic strength of solution, medium composition (anions, cations), presence of denaturants (urea, guanidine chloride) or stabilizers (saccharose), temperature regime, agitation. Since polymorphism is potentially crucial for human diseases and may underlie the natural variability of some amyloid diseases, in this review we focus attention on polymorphism that is an important biophysical difference between native protein folding suggesting correspondence between the amino acid sequence and unique folding state, and formation of amyloid fibrils, when the same amino acid sequence can form amyloid fibrils of different morphology. At present, according to the literature data, we can choose three ways of polymerization of insulin molecules depending on the nucleus size. The first suggests that fibrillogenesis can occur through assembly of insulin monomers. The second suggests that precursors of fibrils are dimers, and the third assumes that precursors of fibrils are oligomers. Additional experimental works and new methods of investigation and assessment of results are needed to clarify the general picture of insulin amyloid formation.

Ligand-controlled assembly of hexamers, dihexamers, and linear multihexamer structures by the engineered acylated insulin degludec

Insulin degludec, an engineered acylated insulin, was recently reported to form a soluble depot after subcutaneous injection with a subsequent slow release of insulin and an ultralong glucose-lowering effect in excess of 40 h in humans. We describe the structure, ligand binding properties, and self-assemblies of insulin degludec using orthogonal structural methods. The protein fold adopted by insulin degludec is very similar to that of human insulin. Hexamers in the R(6) state similar to those of human insulin are observed for insulin degludec in the presence of zinc and resorcinol. However, under conditions comparable to the pharmaceutical formulation comprising zinc and phenol, insulin degludec forms finite dihexamers that are composed of hexamers in the T(3)R(3) state that interact to form an R(3)T(3)-T(3)R(3) structure. When the phenolic ligand is depleted and the solvent condition thereby mimics that of the injection site, the quaternary structure changes from dihexamers to a supramolecular structure composed of linear arrays of hundreds of hexamers in the T(6) state and an average molar mass, M(0), of 59.7 × 10(3) kg/mol. This novel concept of self-assemblies of insulin controlled by zinc and phenol provides the basis for the slow action profile of insulin degludec. To the best of our knowledge, this report for the first time describes a tight linkage between quaternary insulin structures of hexamers, dihexamers, and multihexamers and their allosteric state and its origin in the inherent propensity of the insulin hexamer for allosteric half-site reactivity.

Insulin aspart has a shorter duration of action than human insulin over a wide dose-range

AIMS

Regular human insulin (RHI) at high doses shows prolongation of its duration of action potentially leading to late postprandial hypoglycaemia. This study compared late metabolic activity (4-12 and 6-12 h post-dosing) and duration of action (time to reach late half-maximal activity) over a range of doses between insulin aspart (IAsp) and RHI.

METHODS

Pharmacokinetic and pharmacodynamic properties of subcutaneous IAsp and RHI (6, 12 and 24 (I)U) were compared in 16 healthy subjects in this double-blind, randomized, six-way crossover glucose clamp study.

RESULTS

With increasing doses of both insulins, metabolic activity, insulin exposure, maximum metabolic effect and maximum serum insulin concentration increased linearly. Late metabolic activity was lower for IAsp than RHI at all doses, reaching statistical significance (p < 0.05) for 12 and 24 (I)U. Likewise, IAsp had a shorter duration of action at all doses (p < 0.01) and reached time to 80% of total metabolic activity earlier at doses of 12 and 24 (I)U (p < 0.05). IAsp, compared with RHI, showed a higher maximum metabolic effect at 12 and 24 (I)U (p < 0.0001) and a stronger early metabolic activity for all three doses (p < 0.05).

CONCLUSIONS

IAsp showed a shorter duration of action and, particularly with doses of 12 and 24 (I)U, less late metabolic activity than RHI. These properties might contribute to the lower incidence of hypoglycaemia observed with IAsp versus RHI in clinical trials as lower late metabolic activity should decrease the risk of late postprandial hypoglycaemia.

Insulin initiation in type 2 diabetes: what are the treatment regimen options and how can we best help patients feel empowered?

PURPOSE

This article summarizes treatment regimens and issues involved in initiating insulin therapy in type 2 diabetes (T2D). Progressive deterioration of beta-cell mass and function characterizes the course of T2D. Following diet and exercise, oral antidiabetic drugs (OADs), and incretin therapies, many patients require insulin, but initiation is often delayed until complications develop.

DATA SOURCES

Published guidelines for the management of T2D, primary and review articles, and Food and Drug Administration (FDA) prescribing information.

CONCLUSIONS

The diabetes nurse practitioner should encourage patients to initiate insulin when appropriate; patients need to know that this represents a natural step in treatment, not a personal failing. Initiation often occurs when OADs no longer confer adequate glycemic control. Treatment regimens available include once-daily basal insulin, sometimes with addition of prandial insulin, or premix/biphasic insulin. Insulin analogs confer less risk of hypoglycemia and weight gain, and greater dosing flexibility compared with conventional insulins. Insulin efficacy may be enhanced by continuing metformin and/or incretin therapies, while discontinuing other drugs as appropriate.

IMPLICATIONS FOR PRACTICE

The well-versed diabetes nurse practitioner assists the patient in selecting the most appropriate option for his/her specific needs. It is essential to help patients overcome barriers, including fears of injection pain, public embarrassment, and hypoglycemia risk.

Ultra-rapid absorption of recombinant human insulin induced by zinc chelation and surface charge masking

BACKGROUND

In order to enhance the absorption of insulin following subcutaneous injection, excipients were selected to hasten the dissociation rate of insulin hexamers and reduce their tendency to reassociate postinjection. A novel formulation of recombinant human insulin containing citrate and disodium ethylenediaminetetraacetic acid (EDTA) has been tested in clinic and has a very rapid onset of action in patients with diabetes. In order to understand the basis for the rapid insulin absorption, in vitro experiments using analytical ultracentrifugation, protein charge assessment, and light scattering have been performed with this novel human insulin formulation and compared with a commercially available insulin formulation [regular human insulin (RHI)].

METHOD

Analytical ultracentrifugation and dynamic light scattering were used to infer the relative distributions of insulin monomers, dimers, and hexamers in the formulations. Electrical resistance of the insulin solutions characterized the overall net surface charge on the insulin complexes in solution.

RESULTS

The results of these experiments demonstrate that the zinc chelating (disodium EDTA) and charge-masking (citrate) excipients used in the formulation changed the properties of RHI in solution, making it dissociate more rapidly into smaller, charge-masked monomer/dimer units, which are twice as rapidly absorbed following subcutaneous injection than RHI (Tmax 60 ± 43 versus 120 ± 70 min).

CONCLUSIONS

The combination of rapid dissociation of insulin hexamers upon dilution due to the zinc chelating effects of disodium EDTA followed by the inhibition of insulin monomer/dimer reassociation due to the charge-masking effects of citrate provides the basis for the ultra-rapid absorption of this novel insulin formulation.

Insulin fibrillation and protein design: topological resistance of single-chain analogs to thermal degradation with application to a pump reservoir

Insulin is susceptible to thermal fibrillation, a misfolding process that leads to nonnative cross-β assembly analogous to pathological amyloid deposition. Pharmaceutical formulations are ordinarily protected from such degradation by sequestration of the susceptible monomer within native protein assemblies. With respect to the safety and efficacy of insulin pumps, however, this strategy imposes an intrinsic trade-off between pharmacokinetic goals (rapid absorption and clearance) and the requisite physical properties of a formulation (prolonged shelf life and stability within the reservoir). Available rapid-acting formulations are suboptimal in both respects; susceptibility to fibrillation is exacerbated even as absorption is delayed relative to the ideal specifications of a closed-loop system. To circumvent this molecular trade-off, we exploited structural models of insulin fibrils and amyloidogenic intermediates to define an alternative protective mechanism. Single-chain insulin (SCI) analogs were shown to be refractory to thermal fibrillation with maintenance of biological activity for more than 3 months under conditions that promote the rapid fibrillation and inactivation of insulin. The essential idea exploits an intrinsic incompatibility between SCI topology and the geometry of cross-β assembly. A peptide tether was thus interposed between the A- and B-chains whose length was (a) sufficiently long to provide the "play" needed for induced fit of the hormone on receptor binding and yet (b) sufficiently short to impose a topological barrier to fibrillation. Our findings suggest that ultrastable monomeric SCI analogs may be formulated without protective self-assembly and so permit simultaneous optimization of pharmacokinetics and reservoir life.

Intrinsic fibrillation of fast-acting insulin analogs

BACKGROUND

Aggregation of insulin into insoluble fibrils (fibrillation) may lead to complications for diabetes patients such as reduced insulin potency, occlusion of insulin delivery devices, or potentially increased immunological potential. Even after extensive investigation of fibril formation in regular human insulin, there are little published data about the intrinsic fibrillation of fast-acting analogs. This article investigates and compares the intrinsic fibrillation of three fast-acting insulin analogs--lispro, aspart, and glulisine--as a function of their primary protein structure and exclusive of the stabilizing excipients that are added to their respective commercial formulations.

METHODS

The insulin analogs underwent a buffer exchange into phosphate-buffered saline to remove formulation excipients and then were heated and agitated to characterize intrinsic fibrillation potentials devoid of excipient stabilizing effects. Different analytical methods were used to determine the amount of intrinsic fibrillation for the analogs. After initial lag times, intrinsic fibrillation was detected by an amyloid-specific stain. Precipitation of insulin was confirmed by ultraviolet analysis of soluble insulin and gravimetric measurement of insoluble insulin. Electron microscopy showed dense fibrous material, with individual fibrils that are shorter than typical insulin fibrils. Higher resolution kinetic analyses were carried out in 96-well plates to provide more accurate measures of lag times and fibril growth rates.

RESULTS

All three analogs exhibited longer lag times and slower intrinsic fibrillation rates than human insulin, with glulisine and lispro rates slower than aspart. This is the first study comparing the intrinsic fibrillation of fast-acting insulin analogs without the stabilizing excipients found in their commercial formulations.

CONCLUSIONS

Data show different intrinsic fibrillation potentials based on primary molecular structures when the formulation excipients that are critical for stability are absent. Understanding intrinsic fibrillation potential is critical for evaluating insulin analog stability and device compatibility.

Insulins: past, present, and future

This article highlights selected milestones in insulin discovery and its continued development as a pivotal therapy for diabetes. The last 90 years have witnessed tremendous progress in insulin therapy, from the initial crude, yet life-saving, animal insulin extracts to novel human insulin analogues. Although the complete physiologic replacement of insulin is inherently difficult to achieve with open-loop subcutaneously administered insulin, the continued development of improved injectable insulin formulations with superior pharmacokinetics and pharmacodynamics will enhance glucose control, and represents important clinical advances in the treatment of both type 1 and type 2 diabetes.

Insulin administration: selecting the appropriate needle and individualizing the injection technique

INTRODUCTION

Patients with diabetes who receive insulin therapy often fail to meet their targets for metabolic control with insulin injections. Their inadequate glycemic control may be related to incorrect injection procedure.

AREAS COVERED

This review examines the latest data related to insulin injection and needle characteristics, which play an integral role in patient satisfaction. Searches of Medline and Cumulative Index to Nursing and Allied Health Literature databases were conducted. Results show that optimal insulin injection can facilitate glycemic control in pediatric and adult patients. In general, needles shorter than 8 mm are appropriate for normal weight, obese pediatric and adult patients. However, body mass index, gender, race, age and injection site can influence the depth of subcutaneous tissue and thus, the desired needle size and injection technique. Although the abdomen, thighs and buttocks are all recommended injection sites, abdominal injections disperse insulin slightly more rapidly than thigh injections.

EXPERT OPINION

Wider acceptance of needles shorter than 6 mm will occur with more evidence of their safety and efficacy, particularly in children. Development of shorter and thinner needles to make injections even easier and less burdensome may be expected in the future.

Basal insulin: physiology, pharmacology, and clinical implications

Primary goals in the treatment of type 2 diabetes mellitus (T2DM) include lowering blood glucose levels sufficiently to prevent micro- and macrovascular complications while limiting side effects, such as hypoglycemia and excessive weight gain. Patients with T2DM are typically treated initially with oral antidiabetes agents; however, as the disease progresses, most will require insulin to maintain glycemic control. Often insulin therapy is initiated with basal insulin, and the objective of this article is to present the conceptual aspects of basal insulin therapy and use these concepts to illustrate important clinical aspects. This will be accomplished within a broader contextual discussion of the normal physiologic patterns of insulin secretion, which consist of sustained levels of basal insulin production throughout the day, superimposed with bursts of insulin secretion following a meal (termed bolus or prandial insulin secretion) that slowly decay over 1 to 3 hours. Long-acting basal insulin analogs form a key component of basal-bolus therapy and provide basal support for patients with T2DM. Insulin therapy is often initiated with basal insulin, and newer long-acting analogs, such as insulin glargine and insulin detemir, provide steady, reliable basal insulin coverage in addition to significant advantages over traditional long-acting insulins. This article will integrate conceptual aspects of basal insulin therapy in the context of physiology, molecular pharmacology, and clinical implications of modern basal insulin analogs to provide a foundational understanding of basal insulin biology and physiology.

Insights in regulated bioanalysis of human insulin and insulin analogs by immunoanalytical methods

Despite the long and illustrious history of insulin and insulin analogs as important biotherapeutics, the regulated bioanalysis (in this article, regulated bioanalysis refers to the formalized process for generating bioanalytical data to support pharmacokinetic and toxicokinetic assessments intended for development of insulin and insulin analogs as biotherapeutics, as opposed to the analytical process used for measuring insulin as a biomarker) of these peptides remains a challenging endeavor for a number of reasons. Paramount is the fact that the therapeutic concentrations are often low in serum/plasma and not too dissimilar from the endogenous level, particularly in patients with insulin resistance, such as Type 2 diabetes mellitus. Accordingly, this perspective was written to provide helpful background information for the design and conduct of immunoassays to support regulated bioanalysis of insulin and insulin analogs. Specifically, it highlights the technical challenges for determination of insulin and insulin analogs by immunoanalytical methods that are intended to support evaluations of pharmacokinetics and toxicokinetics. In a broader sense, this perspective describes the general bioanalytical issues that are common to regulated bioanalysis of peptides and articulates some of the bioanalytical differences between conventional monoclonal antibodies and peptide therapeutics.

Comparison of pharmacokinetic properties, physicochemical stability, and pump compatibility of 3 rapid-acting insulin analogues-aspart, lispro, and glulisine

OBJECTIVE

To compare how the rapid-acting insulin analogues (RAIAs) aspart, lispro, and glulisine perform in continuous subcutaneous insulin infusion (CSII) therapy regarding (1) pharmacokinetic properties, (2) chemical and physical stability, and (3) pump compatibility.

METHODS

PubMed was searched for articles pertaining to the use of RAIAs in CSII, without a restriction on the time period.

RESULTS

These RAIAs have pharmacokinetic profiles that more closely mimic endogenous insulin in comparison with regular human insulin and tend to produce less hypoglycemia. Among these RAIAs, the rates of absorption and clinical efficacy in terms of glycemic control were similar. Although glulisine showed a faster onset of action in some studies with aspart and lispro, this advantage lasted only for a maximum of 1 hour, after which results were similar for glulisine and aspart or lispro. Each RAIA is created by making minor amino acid substitutions to the regular human insulin molecule and adding a stabilizer to help prevent fibrillation. A series of chemical and covalent changes affecting the primary structure of an insulin preparation, however, may cause decomposition during storage, handling, and use, diminishing the potency of the insulin molecule while contained in an insulin pump. Precipitation, fibrillation, and occlusion may ensue, undermining compatibility for CSII pump use. Aspart has demonstrated the greatest chemical and physical stability in the insulin pump, with the lowest rates of overall occlusion in comparison with lispro and glulisine (aspart 9.2%, lispro 15.7%, and glulisine 40.9%; P<.01).

CONCLUSION

Aspart is the most compatible of the 3 RAIAs for pump use.

Injectable in situ forming biodegradable chitosan-hyaluronic acid based hydrogels for adipose tissue regeneration

An injectable, biodegradable and glucose-responsive hydrogel derived from natural polysaccharide derivatives was synthesized to deliver adipogenic factor of insulin in vitro for adipose tissue engineering. The biodegradable hydrogel based N-succinyl-chitosan (SCS) and aldehyde hyaluronic acid (AHA) with covalently conjugated glucose oxidase and catalase. The gelation is attributed to the Schiff-base reaction between amino and aldehyde groups of SCS and AHA, respectively. The morphologies and compressive modulus of the freeze-dried hydrogels demonstrated that the incorporated insulin and enzymes results in the formation of a tighter network structure in composite hydrogels. The immobilized enzymes triggered conversion of glucose reduces the pH value of the microenvironment, and results in hydrolysis and increasing swelling of the network basing on Schiff-base cross-linking. The pH inside the hydrogel, kept in PBS solution at pH 7.4 and 37°C, linearly dropped from 7.40 to 7.17 during 4 h of initial period, then slowly increased to 7.36 after 24 h. Correspondingly, the swelling ratio increased from 20.8 to 28.6 at 37°C in PBS with 500 mg/dL glucose. In PBS buffer with 500 mg/dL glucose, about 10.8% of insulin was released from the hydrogel after 8 h of incubation while upon observation. The results demonstrated that the adipogenic factor of insulin would be released from this biodegradable hydrogel device into the local microenvironment in a controlled fashion by the swelling of hydrogel network. These preliminary studies indicate that the biodegradable and glucose-responsive hydrogel may have potential uses in adipose tissue engineering applications.