Absorption kinetics of insulin after subcutaneous administration

BioJect: An in vitro platform to explore release dynamics of peptides in subcutaneous drug delivery

Predicting the release performance of subcutaneous (SC) drug formulations is challenging due to the complex interplay between physicochemical properties and the physiological microenvironment, which includes the extracellular matrix (ECM), fluid composition, and fluid availability, factors that collectively influence bioavailability and absorption rates. The ECM often acts as a bandpass filter modulated by local ion and protein content. In this study, we introduce the BioJect cell, a modern release test method based on the compendial flow-through cell, integrating a perfusion system with customizable biomatrix components. We systematically investigated the release mechanisms of four insulin formulations: regular human insulin, insulin aspart, insulin glulisine, and Neutral Protamine Hagedorn (NPH) insulin. A modified simulated subcutaneous interstitial fluid (mSSIF) comprising multiple components of the SC physiological environment was employed. It incorporates important ions and proteins (138.5 mM sodium, 10 mM potassium, 1.8 mM calcium, 0.8 mM magnesium, 111.3 mM chloride, 28 mM bicarbonate, 0.5 mM sulfate, 5 mM acetate, 4.2 mM phosphate, 30 g/L total protein added as bovine serum albumin). Our release test method discriminated the tested formulations under varying biorelevant conditions, demonstrating its biopredictive capabilities. Notably, we discovered a previously undocumented albumin binding affecting the release rate of insulin glulisine, likely occurring in the low-shear environment of SC tissue only. Additionally, the inclusion of biorelevant components like hyaluronic acid and collagen into the biomatrix of the BioJect cell provided profound insights into potential absorption and release mechanisms, supported by two in vitro-in vivo relationships (level C and level A). The BioJect cell represents a significant advancement in simulating the SC environment for drug release testing. Our findings highlight the importance of considering protein binding and ECM components in predicting drug absorption, offering a promising tool for the development and optimization of SC formulations.

Pharmacokinetic differences between subcutaneous injection and intradermal microneedle delivery of protein therapeutics

Protein therapeutics are essential in the treatment of various diseases, but most of them require parenteral administration. Since intravenous and subcutaneous injections are associated with discomfort and pain, other routes have been investigated including intradermal microneedle delivery. Microneedles are shorter than hypodermic needles and therefore minimize contact with pain receptors in deeper skin layers. But the differences in anatomical and physiological characteristics of dermis and subcutis can potentially result in varying protein penetration through the skin, absorption, and metabolism. This review summarizes pharmacokinetic studies that compare the administration of protein therapeutics by subcutaneous injections and different types of microneedles intradermally including hollow, dissolvable, coated, and hydrogel-forming microneedles. Across animal and human studies, hollow microneedle delivery resulted in quicker and higher peak plasma levels of proteins and comparable bioavailability to subcutaneous injections potentially due to the extensive network of lymphatic and blood vessels in the dermis. In case of dissolvable and coated microneedles, drug release kinetics depend on component materials. The dissolution of polymer excipients can slow the release and permeation of protein therapeutics at the administration site and thereby delay absorption. The understanding of drug penetration through different skin layers, its absorption into blood capillaries or lymphatics, and dermal metabolism remains limited. Additionally, the effects of these processes on the differences in pharmacokinetic profiles of proteins following intradermal microneedle administration are not well understood. Greater insights are required for the development of the next generation of intradermal microneedle biotherapeutics.

Deciphering Pathways and Thermodynamics of Protein Assembly Using Native Mass Spectrometry

Protein oligomerization regulates many critical physiological processes, and its dysregulation can contribute to dysfunction and diseases. Elucidating the assembly pathways and quantifying their underlying thermodynamic and kinetic parameters are crucial for a comprehensive understanding of biological processes and for advancing therapeutics targeting abnormal protein oligomerization. Established binding assays, with limited mass precision, often rely on simplified models for data interpretation. In contrast, high-resolution native mass spectrometry (nMS) can directly determine the stoichiometry of biomolecular complexes in vitro. However, quantification is hindered by the fact that the relative abundances of gas-phase ions generally do not reflect solution concentrations due to nonuniform response factors. Recently, slow mixing mode (SLOMO)-nMS, which can quantify the relative response factors of interacting species, has been demonstrated to reliably measure the affinity (Kd) of binary biomolecular complexes. Here, we introduce an extended form of SLOMO-nMS that enables simultaneous quantification of the thermodynamics in multistep association reactions. Application of this method to homo-oligomerization of concanavalin A and insulin confirmed the reliability of the assay and uncovered details about the assembly processes that had previously resisted elucidation. Results acquired using SLOMO-nMS implemented with charge detection shed new light on the binding of recombinant human angiotensin-converting enzyme 2 and the SARS-CoV-2 spike protein. Importantly, new assembly pathways were uncovered, and the affinities of these interactions, which regulate host cell infection, were quantified. Together, these findings highlight the tremendous potential of SLOMO-nMS to accelerate the characterization of protein assembly pathways and thermodynamics and, in so doing, enhance fundamental biological understanding and facilitate therapeutic development. https://orcid.org/0000-0002-3389-7112.

Evaluating insulindysregulation in horses: A two-step insulin-tolerance test using porcine zinc insulin

In insulin dysregulation, hyperinsulinemia (HI) can be accompanied by peripheral insulin resistance (IR) in horses, which can be diagnosed with an insulin-tolerance test (ITT). The administration of 0.1 IU/kg body weight of recombinant regular human insulin (RHI) should elicit a 50 % reduction of the initial blood glucose concentration at 30 min after insulin administration in insulin sensitive horses. Compared to RHI, porcine zinc insulin (PZI) is veterinary-approved and therefore easier accessible for many practitioners. The aim of this study was to compare the insulin and glucose dynamics during a standard ITT with RHI to an ITT performed with PZI. Twelve Icelandic horses were subjected to an ITT with RHI (ITT-RHI) and with PZI (ITT-PZI) at same dosages in a randomised crossover design. The insulin and glucose dynamics that resulted from these tests were compared, and the consistency of classification into insulin-sensitive and IR categories was evaluated. No complications were observed with the use of either RHI or PZI in ITT. A good correlation of the test results was observed (r = 0.88; P < 0.001). The blood glucose concentrations and the percentage reduction in glucose concentration did not differ significantly between the two tests (P = 0.053), but four out of twelve horses were classified as IR in the ITT-RHI whereas with the ITT-PZI seven out of twelve horses were classified as IR with the 50 % glucose reduction from baseline. Based on the Youden index, when using the ITT-PZI, an adjusted cut-off value for blood glucose reduction of 40 % at 30 min resulted in better test performance. With consideration for the seemingly weaker effect of PZI and the adjusted cut-off value, PZI can be an appropriate substitute to RHI in an ITT.

Advancements in oral insulin: A century of research and the emergence of targeted nanoparticle strategies

With the growing prevalence of diabetes, there is an urgent demand for a user‐friendly treatment option that minimizes side effects related to the use of subcutaneous injections. Scientists have dedicated over a century to developing an oral dosage form of insulin that can be administrated orally. The oral route of administration is the most desirable route for regularly dosed drugs in terms of safety and patient compliance. However, oral delivery of insulin remains a formidable challenge due to its intrinsically limited ability to cross the intestinal epithelium membrane and susceptibility to enzymatic degradation. This article reviews oral insulin research over the past decade, with a particular focus on surface modifications of nanoparticles (NPs). Various strategies involving controlling surface charges, utilizing protective proteins, and targeting specific receptors with ligands have been explored. Notably, surface modifications of the NPs for targeting specific intestinal receptors have shown promise in enhancing insulin oral absorption and bioavailability. Advanced technologies such as oral microneedles and gene therapy have also been developed, but their safety requires further assessment. Despite encouraging preclinical results across numerous strategies, the current clinical evidence is less optimistic. In summary, the present findings highlight the substantial journey that still lies ahead before achieving successful oral delivery of insulin.

Practical Applications: This review provides a summary of recent progress in oral insulin delivery, particularly highlighting surface‐modified functional nanoparticles serving as an effective drug delivery system, which offers valuable information to the researchers. Due to the limited effectiveness of oral protein drugs caused by biological barriers, innovative technologies and drug delivery systems have been developed to overcome these obstacles and achieve therapeutic goals. This review concluded that surface modifications to nanoparticles can improve insulin stability and permeability, thereby enhancing oral bioavailability. It could assist researchers in developing more effective and patient‐friendly oral drug delivery systems.

The Basis for Weekly Insulin Therapy: Evolving Evidence With Insulin Icodec and Insulin Efsitora Alfa

Basal insulin continues to be a vital part of therapy for many people with diabetes. First attempts to prolong the duration of insulin formulations were through the development of suspensions that required homogenization prior to injection. These insulins, which required once- or twice-daily injections, introduced wide variations in insulin exposure contributing to unpredictable effects on glycemia. Advances over the last 2 decades have resulted in long-acting, soluble basal insulin analogues with prolonged and less variable pharmacokinetic exposure, improving their efficacy and safety, notably by reducing nocturnal hypoglycemia. However, adherence and persistence with once-daily basal insulin treatment remains low for many reasons including hypoglycemia concerns and treatment burden. A soluble basal insulin with a longer and flatter exposure profile could reduce pharmacodynamic variability, potentially reducing hypoglycemia, have similar efficacy to once-daily basal insulins, simplify dosing regimens, and improve treatment adherence. Insulin icodec (Novo Nordisk) and insulin efsitora alfa (basal insulin Fc [BIF], Eli Lilly and Company) are 2 such insulins designed for once-weekly administration, which have the potential to provide a further advance in basal insulin replacement. Icodec and efsitora phase 2 clinical trials, as well as data from the phase 3 icodec program indicate that once-weekly insulins provide comparable glycemic control to once-daily analogues, with a similar risk of hypoglycemia. This manuscript details the technology used in the development of once-weekly basal insulins. It highlights the clinical rationale and potential benefits of these weekly insulins while also discussing the limitations and challenges these molecules could pose in clinical practice.

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.

Factors influencing bioequivalence evaluation of insulin biosimilars based on a structural equation model

Objective: This study aimed to explore the factors affecting the bioequivalence of test and reference insulin preparations so as to provide a scientific basis for the consistency evaluation of the quality and efficacy of insulin biosimilars.

Methods: A randomized, open, two-sequence, single-dose, crossover design was used in this study. Subjects were randomly divided into TR or RT groups in equal proportion. The glucose infusion rate and blood glucose were measured by a 24-h glucose clamp test to evaluate the pharmacodynamic parameters of the preparation. The plasma insulin concentration was determined by liquid chromatography–mass spectrometry (LC-MS/MS) to evaluate pharmacokinetic parameters. WinNonlin 8.1 and SPSS 23.0 were applied for PK/PD parameter calculation and statistical analysis. The structural equation model (SEM) was constructed to analyze the influencing factors of bioequivalence by using Amos 24.0.

Results: A total of 177 healthy male subjects aged 18–45 years were analyzed. Subjects were assigned to the equivalent group (N = 55) and the non-equivalent group (N = 122) by bioequivalence results, according to the EMA guideline. Univariate analysis showed statistical differences in albumin, creatinine, Tmax, bioactive substance content, and adverse events between the two groups. In the structural equation model, adverse events (β = 0.342; p &lt; 0.001) and bioactive substance content (β = −0.189; p = 0.007) had significant impacts on the bioequivalence of two preparations, and the bioactive substance content significantly affected adverse events (β = 0.200; p = 0.007).

Conclusion: A multivariate statistical model was used to explore the influencing factors for the bioequivalence of two preparations. According to the result of the structural equation model, we proposed that adverse events and bioactive substance content should be optimized for consistency evaluation of the quality and efficacy of insulin biosimilars. Furthermore, bioequivalence trials of insulin biosimilars should strictly obey inclusion and exclusion criteria to ensure the consistency of subjects and avoid confounding factors affecting the equivalence evaluation.

Enhanced hexamerization of insulin via assembly pathway rerouting revealed by single particle studies

Insulin formulations with diverse oligomerization states are the hallmark of interventions for the treatment of diabetes. Here using single-molecule recordings we firstly reveal that insulin oligomerization can operate via monomeric additions and secondly quantify the existence, abundance and kinetic characterization of diverse insulin assembly and disassembly pathways involving addition of monomeric, dimeric or tetrameric insulin species. We propose and experimentally validate a model where the insulin self-assembly pathway is rerouted, favoring monomeric or oligomeric assembly, by solution concentration, additives and formulations. Combining our practically complete kinetic characterization with rate simulations, we calculate the abundance of each oligomeric species from nM to mM offering mechanistic insights and the relative abundance of all oligomeric forms at concentrations relevant both for secreted and administrated insulin. These reveal a high abundance of all oligomers and a significant fraction of hexamer resulting in practically halved bioavailable monomer concentration. In addition to providing fundamental new insights, the results and toolbox presented here can be universally applied, contributing to the development of optimal insulin formulations and the deciphering of oligomerization mechanisms for additional proteins.

Vasodilatory effects of glucagon: A possible new approach to enhanced subcutaneous insulin absorption in artificial pancreas devices

Patients with diabetes mellitus type 1 depend on exogenous insulin to keep their blood glucose concentrations within the desired range. Subcutaneous bihormonal artificial pancreas devices that can measure glucose concentrations continuously and autonomously calculate and deliver insulin and glucagon infusions is a promising new treatment option for these patients. The slow absorption rate of insulin from subcutaneous tissue is perhaps the most important factor preventing the development of a fully automated artificial pancreas using subcutaneous insulin delivery. Subcutaneous insulin absorption is influenced by several factors, among which local subcutaneous blood flow is one of the most prominent. We have discovered that micro-doses of glucagon may cause a substantial increase in local subcutaneous blood flow. This paper discusses how the local vasodilative effects of micro-doses of glucagon might be utilised to improve the performance of subcutaneous bihormonal artificial pancreas devices. We map out the early stages of our hypothesis as a disruptive novel approach, where we propose to use glucagon as a vasodilator to accelerate the absorption of meal boluses of insulin, besides using it conventionally to treat hypoglycaemia.

Photoacoustic imaging reveals mechanisms of rapid-acting insulin formulations dynamics at the injection site

OBJECTIVE

Ultra-rapid insulin formulations control postprandial hyperglycemia; however, inadequate understanding of injection site absorption mechanisms is limiting further advancement. We used photoacoustic imaging to investigate the injection site dynamics of dye-labeled insulin lispro in the Humalog® and Lyumjev® formulations using the murine ear cutaneous model and correlated it with results from unlabeled insulin lispro in pig subcutaneous injection model.

METHODS

We employed dual-wavelength optical-resolution photoacoustic microscopy to study the absorption and diffusion of the near-infrared dye-labeled insulin lispro in the Humalog and Lyumjev formulations in mouse ears. We mathematically modeled the experimental data to calculate the absorption rate constants and diffusion coefficients. We studied the pharmacokinetics of the unlabeled insulin lispro in both the Humalog and Lyumjev formulations as well as a formulation lacking both the zinc and phenolic preservative in pigs. The association state of insulin lispro in each of the formulations was characterized using SV-AUC and NMR spectroscopy.

RESULTS

Through experiments using murine and swine models, we show that the hexamer dissociation rate of insulin lispro is not the absorption rate-limiting step. We demonstrated that the excipients in the Lyumjev formulation produce local tissue expansion and speed both insulin diffusion and microvascular absorption. We also show that the diffusion of insulin lispro at the injection site drives its initial absorption; however, the rate at which the insulin lispro crosses the blood vessels is its overall absorption rate-limiting step.

CONCLUSIONS

This study provides insights into injection site dynamics of insulin lispro and the impact of formulation excipients. It also demonstrates photoacoustic microscopy as a promising tool for studying protein therapeutics. The results from this study address critical questions around the subcutaneous behavior of insulin lispro and the formulation excipients, which could be useful to make faster and better controlled insulin formulations in the future.

Numerical Simulation of Insulin Depot Formation in Subcutaneous Tissue Modeled as a Homogeneous Anisotropic Porous Media

In this study, a numerical model of insulin depot formation in the subcutaneous adipose tissue of humans has been developed using the commercial computational fluid dynamics software. A better understanding of the underlying mechanisms can be helpful in the development of novel insulin administration devices and cannula geometries. Developing a model of insulin depot formation can provide faster results compared to extensive experimental studies which are typically done on porcine tissues. The injection method considered in this simulation involves an insulin pump that uses a rapid acting U100 insulin analogue. The depot formation has been studied by simulating Bolus injections ranging from 5 to 15 units of insulin, which corresponds to volumes of 50-150 μL. The insulin is injected into modeled subcutaneous tissues typically present in human abdominal regions. The subcutaneous tissue has been modeled as a fluid-saturated porous media. An anisotropic approach has been used to define the tissue permeability. The value of the porosity in parallel and perpendicular directions has been varied to modify the viscous resistance to the flow in these directions. The developed model has been validated by comparing with published experimental results, which show qualitative similarities in disk-shaped insulin depot formation. The validated model is then used to study formation of insulin depot inside the subcutaneous tissue at varying insulin flow rates involving different cannula geometries and arrays. The numerical model has been found to be an effective option to evaluate new cannula designs prior to the manufacturing and testing of prototypes, which can be rather time consuming and expensive.

Food intake rather than blood glucose levels affects the pharmacokinetic profile of insulin aspart in pigs

In humans, food intake and glucose infusion have been reported to increase subcutaneous blood flow. Since local blood flow influences the rate of insulin absorption from the subcutaneous tissue, we hypothesised that an increase in blood glucose levels-occurring as the result of glucose infusion or food intake-could modulate the pharmacokinetic properties of subcutaneously administered insulin. The pharmacokinetic profile of insulin aspart was assessed in 29 domestic pigs that were examined in a fed and fasted state or included in hyperinsulinaemic clamp studies of 4 vs. 10 mmol/L glucose prior to subcutaneous (30 nmol) or intravenous (0.1 nmol/kg) insulin administration. Results showed that food intake compared to fasting accelerated absorption and decreased clearance of insulin aspart (P < 0.05). Furthermore, higher c-peptide but also glucagon levels were observed in fed compared to fasted pigs (P < 0.05). The pharmacokinetic profile of insulin aspart did not differ between pigs clamped at 4 vs. 10 mmol/L glucose. Hence, food intake rather than blood glucose levels within normal range modulates the pharmacokinetic properties of insulin aspart upon subcutaneous and intravenous administration in pigs.

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.

Pluronic® F127-mediated control of insulin release rates from NPH microcrystals and blood glucose depression in STZ-induced diabetic rats

Introduction: Neutral protamine Hagedorn (NPH) insulin is an intermediate-acting basal insulin with a long history of clinical use, consisting native human insulin. Its rather undesirable action profile, characterized by a peak release within a few hours, followed by insufficient insulin delivery upon a single subcutaneous (s.c.) dose, is well-documented. This may have been caused by the inherent microcrystal structure involving the basic peptide protamine, as well as the presence of tissue enzyme activities that readily act on protamine at the injection site. This issue may be circumvented by utilizing thermosensitive, erodible Pluronic F127 (PF127) to modulate the kinetics of insulin release from NPH over a period of 24 hours in which the hydrogel is completely eroded.

Methods: Previously, we have shown that insulin release rates in vitro from NPH/PF127 formulations (0-25% PF127) markedly reduced the initial insulin release, especially in the presence of enzyme activity that selectively degraded protamine at 1-5 U/mL. Insulin release over the course of 20 hours was better modulated in the presence of increasing PF127 content. In this study, the insulin formulations (0, 20, and 25% PF127) were administered s.c. (4 U/kg) to streptozotocin (STZ)-induced diabetic rats and blood glucose levels were monitored over 24 hours.

Results: In vivo blood glucose depression profiles in STZ-induced diabetic rats exhibited a similar pattern of control to in vitro data at the single s.c. dose of 4 U/kg, apparently extending the duration of action of NPH over a 24-hour period in the presence of PF127.

Conclusion: Our findings suggest that the undesirable kinetics of insulin release from NPH is significantly influenced by tissue enzyme activity and that the presence of PF127 provided a timely modulation of insulin release from NPH microcrystals in the STZ-induced diabetic rat model.

Critical Low Catastrophe: A Case Report of Treatment-Refractory Hypoglycemia following Overdose of Long-Acting Insulin

Overdose of long-acting insulin can cause unpredictable hypoglycemia for prolonged periods of time. The initial treatment of hypoglycemia includes oral carbohydrate intake as able and/or parenteral dextrose infusion. Refractory hypoglycemia following these interventions presents a clinical challenge in the absence of clear guidelines for management. Octreotide has sometimes been used, but its use is generally limited to sulfonylurea overdose. In this case report, we present a case of refractory hypoglycemia following an overdose of 900 units of long-acting insulin glargine that failed to respond to usual modes of therapy mentioned above. Stress-dose corticosteroids were then initiated, followed by subsequent improvement in IV dextrose and glucagon requirements and blood glucose levels. Hence, corticosteroids may serve as an adjunctive therapy in managing hypoglycemia and can be considered earlier in the course of treatment in patients with refractory hypoglycemia to prevent volume overload, especially when large volumes of dextrose infusions are required.

Factors Influencing Insulin Absorption Around Exercise in Type 1 Diabetes

International charities and health care organizations advocate regular physical activity for health benefit in people with type 1 diabetes. Clinical expert and international diabetes organizations' position statements support the management of good glycemia during acute physical exercise by adjusting exogenous insulin and/or carbohydrate intake. Yet research has detailed, and patients frequently report, variable blood glucose responses following both the same physical exercise session and insulin to carbohydrate alteration. One important source of this variability is insulin delivery to the circulation. With modern insulin analogs, it is important to understand how different insulins, their delivery methods, and inherent physiological factors, influence the reproducibility of insulin absorption from the injection site into circulation. Furthermore, contrary to the adaptive pancreatic response to exercise in the person without diabetes, the physiological and metabolic shifts with exercise may increase circulating insulin concentrations that may contribute to exercise-related hyperinsulinemia and consequent hypoglycemia. Thus, a furthered understanding of factors underpinning insulin delivery may offer more confidence for healthcare professionals and patients when looking to improve management of glycemia around exercise.

Insulin Release from NPH Insulin-Loaded Pluronic® F127 Hydrogel in the Presence of Simulated Tissue Enzyme Activity

Background: Despite the widespread use of newer basal insulins, Natural Protamine Hagedorn (NPH) insulin still represents a well-established basal formulation with its long history of use, featuring the native form of human insulin. However, NPH insulin exhibits an undesirable peak within hours after a single subcutaneous (s.c.) injection, which may lead to hypoglycemia followed by insufficient basal insulin delivery. This may be attributed to the s.c. enzyme activities degrading the protamine in NPH microcrystals. Methods: A thermogelling block copolymer Pluronic® F127 (PF127) was utilized as a protective carrier for NPH microcrystals and as a modulator for insulin release from NPH. NPH insulin-loaded PF127 gel was prepared with varying concentrations of the polymer (15–25%) under mild conditions. The formulations were characterized for their gelling temperature, morphology, gel erosion, and in vitro insulin release, with trypsin concentrations up to 5 U/mL. Results: Scanning electron microscopy (SEM) showed that the integrity of NPH microcrystals was maintained after preparation. The burst release of insulin from NPH was significantly attenuated over the course of ~16h in the presence of PF127 with or without enzyme activity. Conclusion: NPH-PF127 successfully resisted the acceleration of NPH crystal dissolution and insulin release in vitro in the presence of protamine-degrading enzyme activity, warranting further testing.

Pharmacokinetics of Faster and Standard Insulin Aspart During Fully Closed-Loop Insulin Delivery in Type 2 Diabetes

Background: Faster insulin aspart is a novel formulation of insulin aspart aiming to accelerate its subcutaneous absorption. The aim of this study was to compare pharmacokinetics of faster insulin aspart versus standard insulin aspart in adults with type 2 diabetes during closed-loop insulin delivery. Methods: We assessed the pharmacokinetics of faster and standard insulin aspart from data obtained in a randomized double-blind crossover study evaluating fully closed-loop insulin delivery in adults with type 2 diabetes (n = 13, age 59 ± 10 years, BMI 34.5 ± 9.1 kg/m², HbA1c 7.7% ± 1.2% [60 ± 13 mmol/mol]). Blood samples were collected every 15-30 min for 10 h to determine plasma insulin aspart concentration using liquid chromatography mass spectrometry. Time to peak plasma concentration (T_max) was calculated using a two-compartment model. Results:T_max was 68.7 ± 21.6 min for faster aspart and 89.7 ± 31.8 min for aspart (mean paired difference faster aspart minus aspart -15.5 min, 95% CI [-31.6 to 0.6 min], P = 0.06). Metabolic clearance rate did not differ between the two insulins (P = 0.61). Insulin amount delivered during closed-loop with faster aspart positively correlated with T_max (r_S = 0.73, P = 0.01), whereas no statistically significant correlation was found with body mass index (BMI), weight or HbA1C (all P > 0.18). Conclusion: In conclusion, T_max tended to be shorter for faster aspart versus aspart during fully automated closed-loop insulin delivery and positively correlated with the amount of insulin delivered.

Ionic liquid-mediated delivery of insulin to buccal mucosa

Buccal drug delivery offers a potential non-invasive means of delivering therapeutics to patients. Despite the promise, the feasibility of transporting proteins and peptides into systemic circulation from buccal administration remains a daunting challenge. Here, we report the fabrication of a biodegradable polymeric patch for buccal delivery of insulin using chitosan as the mucoadhesive matrix and ionic liquids (ILs)/deep eutectic solvent (DES) as the transport facilitator. Insulin is mixed with ILs/DES made from Choline and Geranic acid (CAGE) to form a viscoelastic CAGE gel and sandwiched between two layers of a biodegradable polymer. The rheological properties of the CAGE gel were dominated by the elastic modulus and suggested a solid-like viscoelastic behavior. CAGE induced a 7-fold increase in the cumulative insulin transport across the ex vivo porcine buccal tissue (~26% of loaded insulin) which was also confirmed by confocal microscopy. The CAGE/insulin patches placed in the rat buccal pouch in vivo lowered blood glucose levels in a dose-dependent manner (up to 50% drop recorded) with no obvious tissue damage at the application site. The pharmacokinetic performance of the delivered insulin indicated a sustained profile as serum insulin levels plateaued after 3 h for the duration of study. The safety and efficacy of the polymeric patch using insulin as a model drug holds significant promise as a platform technology to deliver injectables through the buccal route.

Temporal pressure enhanced topical drug delivery through micropore formation

Transdermal drug delivery uses chemical, physical, or biochemical enhancers to cross the skin barrier. However, existing platforms require high doses of chemical enhancers or sophisticated equipment, use fragile biomolecules, or are limited to a certain type of drug. Here, we report an innovative methodology based on temporal pressure to enhance the penetration of all kinds of drugs, from small molecules to proteins and nanoparticles (up to 500 nm). The creation of micropores (~3 μm2) on the epidermal layer through a temporal pressure treatment results in the elevated expression of gap junctions, and reduced expression of occludin tight junctions. A 1 min treatment of 0.28-MPa allows nanoparticles (up to 500 nm) and macromolecules (up to 20 kDa) to reach a depth of 430-μm into the dermal layer. Using, as an example, the delivery of insulin through topical application after the pressure treatment yields up to 80% drop in blood glucose in diabetic mice.

Towards in vitro in vivo correlation for modified release subcutaneously administered insulins

Therapeutic proteins and peptides are mainly administrated by subcutaneous injection. In vitro release testing of subcutaneous injectables performed using methods that take the structure and environment of the subcutaneous tissue into account may improve predictability of the in vivo behavior and thereby facilitate establishment of in vitro in vivo correlations. The aim of the study was to develop a biopredictive flow-through in vitro release method with a gel-type matrix for subcutaneously administered formulations and to explore the possibility of establishing a level A in vitro in vivo correlation for selected insulin products. A novel gel-based flow-through method with the incorporation of an injection step was used to assess selected commercial insulin formulations with different duration of action (Actrapid®, Mixtard® 30, Insulatard®, Lantus®). The in vitro release method provided the correct rank ordering in relation to the in vivo performance. For the modified release insulins Insulatard® and Lantus®, an in vitro in vivo correlation using non-linear time scaling was established based on the in vitro release data and in vivo subcutaneous absorption data of the ¹²⁵I-labeled insulins taken from literature. Predicted absorption profiles were constructed using the in vitro in vivo correlation and subsequently converted into simulated plasma profiles. The approach taken may be of wider utility in characterizing injectables for subcutaneous administration.

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.

Delayed insulin absorption correlates with alterations in subcutaneous depot kinetics in rats with diet-induced obesity

OBJECTIVE

Obesity is associated with delayed insulin absorption upon subcutaneous (s.c.) dosing in humans. The aim of this study was to investigate whether alterations in depot structure and kinetics of the s.c. injection depot contribute to this delay.

METHODS

Rats fed a high-fat diet (HFD) and low-fat diet (LFD) were included in a series of insulin pharmacokinetic and imaging studies. Injection depots were visualized with micro X-ray computed tomography imaging upon s.c. administration of insulin aspart mixed with the contrast agent iomeprol, and insulin aspart exposure was measured by means of luminescent oxygen channelling immunoassay.

RESULTS

Body weight and fat mass were increased in rats fed an HFD vs. LFD (p < 0.05), whereas the lean mass was not. The HFD group exhibited delayed insulin absorption from the s.c. tissue (p < 0.001). This delay was associated with smaller injection depots upon s.c. dosing (p < 0.05) and correlated with a slower depot disappearance from the s.c. tissue (p < 0.05) compared with the LFD group. Depot disappearance from the s.c. tissue was inversely correlated with body fat mass (p < 0.05).

CONCLUSIONS

Alterations in s.c. injection depot structure and kinetics may play a role in the obesity-associated delay in insulin absorption.

Concentrated insulins: History and critical reappraisal

The earliest marketed insulins were crude acidic formulations with concentrations of ≤10 units/mL. Since the early 1920s, insulins have improved continually, via bioengineering, process, and chemical modifications. Today, most insulin formulations have a concentration of 100 units/mL (U100). However, more concentrated insulin formulations (200, 300, and 500 units/mL; U200, U300, and U500, respectively) are also available. There is a tendency to assume that concentrated insulins are similar, both to each other and to their U100 counterparts, but this is not always the case: two concentrated insulins, namely insulin degludec U200 and insulin lispro U200, are bioequivalent to their U100 counterparts, whereas regular human insulin U500 and insulin glargine U300 are not. The advent of these concentrated insulins offers greater opportunities to provide tailored therapy for patients; it also introduces potential confusion, and highlights the need for prescriber and patient education. Precise and accurate dedicated insulin delivery devices are also necessary for the safe use of these concentrated insulins. Although some clinicians only use concentrated insulin with obese and severely insulin-resistant patients, other patients would also benefit from the reduced injection volume associated with concentrated insulins, or the modified time-action profile of some concentrated insulins. The aim of this review is to enhance understanding of the historic development and the safe and effective use of concentrated insulins in clinical practice.

Concentrated insulins in current clinical practice

New concentrated insulins (exceeding 100 units/mL) and dedicated devices have recently become available, offering new treatment options for people with diabetes, for basal and prandial insulin supplementation. The concentrated insulin formulations range from 2-fold concentration (insulin lispro 200 units/mL) with rapid-acting prandial action to 5-fold concentration (human regular insulin, 500 units/mL) with basal and short-acting prandial actions. Long-acting basal insulins include degludec 200 units/mL and glargine 300 units/mL. Concentrated insulins have been developed with the goal of easing insulin therapy by reducing the volume and number of injections and in some cases making use of altered pharmacokinetic and pharmacodynamic properties. This review summarizes the unique characteristics of each concentrated insulin to help healthcare providers and people with diabetes understand how to best use them.

Insulin depot absorption modeling and pharmacokinetic simulation with insulin glargine 300 U/mL

OBJECTIVE

Mathematical models of insulin absorption have been used to predict plasma insulin concentrations after administration, but few are specifically applicable to insulin glargine, which precipitates subcutaneously after injection.

MATERIALS AND METHODS

The formation and redissolution of subcutaneous depots of insulin glargine 100 U/mL (Gla-100) and insulin glargine 300 U/mL (Gla-300) are modeled. Surface-area-dependent redissolution is introduced to established diffusion and absorption pathways, and pharmacokinetic (PK) profiles are simulated and subsequently validated using experimental data from euglycemic glucose clamp studies. Simulations are used to predict the PK effect of adapting the timing of once-daily insulin injections and of switching from one insulin product to the other. -Results: Simulated PK profiles resemble those previously observed in clinical trials, with Gla-300 providing more gradual and prolonged release of Gla-300 vs. Gla-100, owing to a more compact depot. The predicted PK profile of Gla-300 shows less fluctuation in plasma insulin concentrations than that of Gla-100, and may be better suited to adapting the timing of daily injections to account for variation in daily activities. Simulating a switch from one insulin glargine product to the other results in temporary alteration of previous steady state, but this is regained within ~ 3 days.

CONCLUSION

This study suggests that PK differences between Gla-300 and Gla-100 are a product of the more compact Gla-300 depot and its smaller surface area. The model employed also allowed estimation of insulin glargine concentrations when varying the time interval between injections as well as when switching from one insulin glargine product to the other.
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Factors Affecting the Absorption of Subcutaneously Administered Insulin: Effect on Variability

Variability in the effect of subcutaneously administered insulin represents a major challenge in insulin therapy where precise dosing is required in order to achieve targeted glucose levels. Since this variability is largely influenced by the absorption of insulin, a deeper understanding of the factors affecting the absorption of insulin from the subcutaneous tissue is necessary in order to improve glycaemic control and the long-term prognosis in people with diabetes. These factors can be related to either the insulin preparation, the injection site/patient, or the injection technique. This review highlights the factors affecting insulin absorption with special attention on the physiological factors at the injection site. In addition, it also provides a detailed description of the insulin absorption process and the various modifications to this process that have been utilized by the different insulin preparations available.

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.

New Basal Insulins: a Clinical Perspective of Their Use in the Treatment of Type 2 Diabetes and Novel Treatment Options Beyond Basal Insulin

PURPOSE OF REVIEW

The purpose of this review was to review advances in basal insulin formulations and new treatment options for patients with type 2 diabetes not achieving glycemic targets despite optimized basal insulin therapy.

RECENT FINDINGS

Advances in basal insulin formulations have resulted in products with increasingly favorable pharmacokinetic and pharmacodynamic properties, including flatter, peakless action profiles, less inter- and intra-patient variability, and longer duration of activity. These properties have translated to significantly reduced risk of hypoglycemia (particularly during the night) compared with previous generation basal insulins. When optimized basal insulin therapy is not sufficient to obtain or maintain glycemic goals, various options exist to improve glycemic control, including intensification of insulin therapy with the addition of prandial insulin or changing to pre-mixed insulin and, more recently, the addition of a GLP-1 receptor agonist, either as a separate injection or as a component of one of the new fixed-ratio combinations of a basal insulin and GLP-1 RA. New safer and often more convenient basal insulins and fixed ratio combinations containing basal insulin (and GLP-1 receptor agonist) are available today for patients with type 2 diabetes not achieving glycemic goals. Head-to-head studies comparing the latest generation basal insulins are underway, and future studies assessing the fixed-ratio combinations will be important to better understand their differentiating features.

Development of a Convenient In Vitro Gel Diffusion Model for Predicting the In Vivo Performance of Subcutaneous Parenteral Formulations of Large and Small Molecules

Parenteral delivery remains a compelling drug delivery route for both large- and small-molecule drugs and can bypass issues encountered with oral absorption. For injectable drug products, there is a strong patient preference for subcutaneous administration due to its convenience over intravenous infusion. However, in subcutaneous injection, in contrast to intravenous administration, the formulation is in contact with an extracellular matrix environment that behaves more like a gel than a fluid. This can impact the expected performance of a formulation. Since typical bulk fluid dissolution studies do not accurately simulate the subcutaneous environment, improved in vitro models to help better predict the behavior of the formulation are critical. Herein, we detail the development of a new model system consisting of a more physiologically relevant gel phase to simulate the rate of drug release and diffusion from a subcutaneous injection site using agarose hydrogels as a tissue mimic. This is coupled with continuous real-time data collection to accurately monitor drug diffusion. We show how this in vitro model can be used as an in vivo performance differentiator for different formulations of both large and small molecules. Thus, this model system can be used to improve optimization and understanding of new parenteral drug formulations in a rapid and convenient manner.

Impact of the mode of protraction of basal insulin therapies on their pharmacokinetic and pharmacodynamic properties and resulting clinical outcomes

Manufacturers of insulin products for diabetes therapy have long sought ways to modify the absorption rate of exogenously administered insulins in an effort to better reproduce the naturally occurring pharmacokinetics of endogenous insulin secretion. Several mechanisms of protraction have been used in pursuit of a basal insulin, for which a low injection frequency would provide tolerable and reproducible glucose control; these mechanisms have met with varying degrees of success. Before the advent of recombinant DNA technology, development focused on modifications to the formulation that increased insulin self-association, such as supplementation with zinc or the development of preformed precipitates using protamine. Indeed, NPH insulin remains widely used today despite a frequent need for a twice-daily dosing and a relatively high incidence of hypoglycaemia. The early insulin analogues used post-injection precipitation (insulin glargine U100) or dimerization and albumin binding (insulin detemir) as methods of increasing therapeutic duration. These products approached a 24-hour glucose-lowering effect with decreased variability in insulin action. Newer basal insulin analogues have used up-concentration in addition to precipitation (insulin glargine U300), and multihexamer formation in addition to albumin binding (insulin degludec), to further increase duration of action and/or decrease the day-to-day variability of the glucose-lowering profile. Clinically, the major advantage of these recent analogues has been a reduction in hypoglycaemia with similar glycated haemoglobin control when compared with earlier products. Future therapies may bring clinical benefits through hepato-preferential insulin receptor binding or very long durations of action, perhaps enabling once-weekly administration and the potential for further clinical benefits.

Insulin aspart pharmacokinetics: an assessment of its variability and underlying mechanisms

BACKGROUND

Insulin aspart (IAsp) is used by many diabetics as a meal-time insulin to control post-prandial glucose levels. As is the case with many other insulin types, the pharmacokinetics (PK), and consequently the pharmacodynamics (PD), is associated with clinical variability, both between and within individuals. The present article identifies the main physiological mechanisms that govern the PK of IAsp following subcutaneous administration and quantifies them in terms of their contribution to the overall variability.

MATERIAL AND METHODS

CT scanning data from Thomsen et al. (2012) are used to investigate and quantify the properties of the subcutaneous depot. Data from Brange et al. (1990) are used to determine the effects of insulin chemistry in subcutis on the absorption rate. Intravenous (i.v.) bolus and infusion PK data for human insulin are used to understand and quantify the systemic distribution and elimination (Pørksen et al., 1997; Sjöstrand et al., 2002). PK and PD profiles for type 1 diabetics from Chen et al. (2005) are analyzed to demonstrate the effects of IAsp antibodies in terms of bound and unbound insulin. PK profiles from Thorisdottir et al. (2009) and Ma et al. (2012b) are analyzed in the nonlinear mixed effects software Monolix® to determine the presence and effects of the mechanisms described in this article.

RESULTS

The distribution of IAsp in the subcutaneous depot show an initial dilution of approximately a factor of two in a single experiment. Injected insulin hexamers exist in a chemical equilibrium with monomers and dimers, which depends strongly on the degree of dilution in subcutis, the presence of auxiliary substances, and a variety of other factors. Sensitivity to the initial dilution in subcutis can thus be a cause of some of the variability. Temporal variations in the PK are explained by variations in the subcutaneous blood flow. IAsp antibodies are found to be a large contributor to the variability of total insulin PK in a study by Chen et al. (2005), since only the free fraction is eliminated via the receptors. The contribution of these and other sources of variability to the total variability is quantified via a population PK analysis and two recent clinical studies (Thorisdottir et al., 2009; Ma et al., 2012b), which support the presence and significance of the identified mechanisms.

CONCLUSIONS

IAsp antibody binding, oligomeric transitions in subcutis, and blood flow dependent variations in absorption rate seem to dominate the PK variability of IAsp. It may be possible via e.g. formulation design to reduce some of these variability factors.

Is dynamic autocrine insulin signaling possible? A mathematical model predicts picomolar concentrations of extracellular monomeric insulin within human pancreatic islets

Insulin signaling is essential for -cell survival and proliferation in vivo. Insulin also has potent mitogenic and anti-apoptotic actions on cultured -cells, with maximum effect in the high picomolar range and diminishing effect at high nanomolar doses. In order to understand whether these effects of insulin are constitutive or can be subjected to physiological modulation, it is essential to estimate the extracellular concentration of monomeric insulin within an intact islet. Unfortunately, the in vivo concentration of insulin monomers within the islet cannot be measured directly with current technology. Here, we present the first mathematical model designed to estimate the levels of monomeric insulin within the islet extracellular space. Insulin is released as insoluble crystals that exhibit a delayed dissociation into hexamers, dimers, and eventually monomers, which only then can act as signaling ligands. The rates at which different forms of insulin dissolve in vivo have been estimated from studies of peripheral insulin injection sites. We used this and other information to formulate a mathematical model to estimate the local insulin concentration within a single islet as a function of glucose. Model parameters were estimated from existing literature. Components of the model were validated using experimental data, if available. Model analysis predicted that the majority of monomeric insulin in the islet is that which has been returned from the periphery, and the concentration of intra-islet monomeric insulin varies from 50–300 pM when glucose is in the physiological range. Thus, our results suggest that the local concentration of monomeric insulin within the islet is in the picomolar ‘sweet spot’ range of insulin doses that activate the insulin receptor and have the most potent effects on -cells in vitro. Together with experimental data, these estimations support the concept that autocrine/paracrine insulin signalling within the islet is dynamic, rather than constitutive and saturated.

Subcutaneous administration of nano- and microsuspensions of poorly soluble compounds to rats

The aim of the present study was to evaluate and interpret the pharmacokinetic profiles of two compounds after subcutaneous (s.c.) administration. The compounds have similar physicochemical properties, but are a base (BA99) and an acid (AC88), respectively. The compounds were administered as nano- (5 and 500 µmol/kg) and microsuspensions (5 µmol/kg) s.c. to Sprague-Dawley rats. At the low dose, the exposure was higher for both compounds administered as nanocrystals compared to microparticles. The high dose of the compounds resulted in even higher exposure, but not in a dose-linear manner. The differences in exposure between nano- and microparticles were mainly ascribed to higher dissolution rate and improved solubility for smaller particles. In addition to differences in exposure, there were also differences in the elimination pattern. After s.c. injection of 5 µmol/kg of BA99 as nano- and microsuspensions, the elimination profile was similar as observed earlier after oral administration. However, after injection of the higher dose of BA99 and all formulations of AC88, an extended elimination profile was observed, forming a maintained plateau under the investigated time-period. Essentially, constant plasma levels were caused by a balanced equilibrium between total body clearance of the drug and supply rate of drug from the formulations.

Visualization of subcutaneous insulin injections by x-ray computed tomography

We report how the three-dimensional structure of subcutaneous injections of soluble insulin can be visualized by x-ray computed tomography using an iodine based contrast agent. The injections investigated are performed ex vivo in porcine adipose tissue. Full tomography scans carried out at a laboratory x-ray source with a total acquisition time of about 1 min yield CT-images with an effective pixel size of 109 × 109 μm². The depots are segmented using a modified Chan-Vese algorithm and we are able to observe differences in the shape of the injection depot and the position of the depot in the skin among equally performed injections. To overcome the beam hardening artefacts, which affect the quantitative prediction of the volume injected, we additionally present results concerning the visualization of two injections using synchrotron radiation. The spatial concentration distribution of iodine is calculated to show the dilution of the insulin drug inside the depot. Characterisation of the shape of the depot and the spatial concentration profile of the injected fluid is important knowledge when improving the clinical formulation of an insulin drug, the performance of injection devices and when predicting the effect of the drug through biomedical simulations.

Comparison of the pharmacokinetics of three concentrations of insulin aspart during continuous subcutaneous insulin infusion (CSII) in a pig model

OBJECTIVES

The aim of the study was to investigate the pharmacokinetic properties of insulin aspart (IAsp) in three different concentrations given as a continuous subcutaneous insulin infusion (CSII).

METHODS

A randomized cross-over study was performed in pigs, where IAsp U200, U100 or U20 was given for 8 h with the same total dose. Six pigs were included and blood was sampled during the CSII and 3 h after.

KEY FINDINGS

The half-life (t(1/2) ) was 24.3 (range 17.3-41.3), 28.8 (range 19.6-54.3) and 23.6 (range 17.4-36.8) min for U200, U100 and U20, respectively. The area under the curve per dose (AUC/D) was determined to be 51.2 ± 19.5, 52.3 ± 12.5 and 51.6 ± 6.7 pm × min/kg for U200, U100 and U20, respectively. The steady state plasma concentration (C(ss) ) was 57.5 ± 27.1, 54.3 ± 10.3 and 55.1 ± 8.0 pm (mean ± SD) for U200, U100 and U20, respectively. Time to steady state (T(ss) ) was 110 ± 36, 98 ± 48 and 90 ± 27 min for U200, U100 and U20, respectively.

CONCLUSIONS

In conclusion, no significant difference was found in t(1/2) , AUC/D, C(ss) or T(ss) between the three IAsp concentrations when given at a basal rate in CSII.

Multivariate prediction of subcutaneous glucose concentration in type 1 diabetes patients based on support vector regression

Data-driven techniques have recently drawn significant interest in the predictive modeling of subcutaneous (s.c.) glucose concentration in type 1 diabetes. In this study, the s.c. glucose prediction is treated as a multivariate regression problem, which is addressed using support vector regression (SVR). The proposed method is based on variables concerning: (i) the s.c. glucose profile, (ii) the plasma insulin concentration, (iii) the appearance of meal-derived glucose in the systemic circulation, and (iv) the energy expenditure during physical activities. Six cases corresponding to different combinations of the aforementioned variables are used to investigate the influence of the input on the daily glucose prediction. The proposed method is evaluated using a dataset of 27 patients in free-living conditions. 10-fold cross validation is applied to each dataset individually to both optimize and test the SVR model. In the case where all the input variables are considered, the average prediction errors are 5.21, 6.03, 7.14 and 7.62 mg/dl for 15, 30, 60 and 120 min prediction horizons, respectively. The results clearly indicate that the availability of multivariable data and their effective combination can significantly increase the accuracy of both short-term and long-term predictions.

Accelerating and improving the consistency of rapid-acting analog insulin absorption and action for both subcutaneous injection and continuous subcutaneous infusion using recombinant human hyaluronidase

Rapid-acting insulin analogs were introduced to the market in the 1990s, and these products have improved treatment of diabetes by shortening the optimum delay time between injections and meals. Compared with regular human insulin, rapid-acting insulin formulations also reduce postprandial glycemic excursions while decreasing risk of hypoglycemia. However, the current prandial products are not fast enough for optimum convenience or control. Recombinant human hyaluronidase (rHuPH20) has been used to increase the dispersion and absorption of other injected drugs, and in the case of prandial insulin analogs, it confers both ultrafast absorption and action profiles. Animal toxicology studies have demonstrated excellent tolerability of rHuPH20, and human studies, involving over 60,000 injections of prandial insulin + rHuPH20 to date, have similarly shown excellent safety and tolerability. Studies using rapid-acting analog insulin with rHuPH20 have included clinic-based pharmacokinetic and glucodynamic euglycemic glucose clamp studies, test meal studies, and take-home treatment studies. Administration methods have included subcutaneous injection of coformulations of rapid-acting insulin + rHuPH20 as well as continuous subcutaneous infusion of coformulations or use of pretreatment of newly inserted infusion sets with rHuPH20 followed by standard continuous subcutaneous insulin infusion therapy. These studies have demonstrated acceleration of insulin absorption and action along with improvement in postprandial glycemic excursions and reduction in hypoglycemia risks. Further, rHuPH20 reduces intrasubject variability of insulin absorption and action and provides greater consistency in absorption and action profiles over wear time of an infusion set. Further studies of rHuPH20 in the take-home treatment setting are underway.

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.

Improved postprandial glycemic control in patients with type 2 diabetes from subcutaneous injection of insulin lispro with hyaluronidase

BACKGROUND

Coinjection of hyaluronidase has been shown to accelerate insulin absorption in healthy volunteers and patients with type 1 diabetes mellitus. This study was undertaken to compare the postprandial glycemic response of patients with type 2 diabetes mellitus (T2DM) administered insulin lispro with and without recombinant human hyaluronidase (rHuPH20) and regular human insulin (RHI) with rHuPH20.

METHODS

This double-blind three-way crossover study compared the insulin pharmacokinetics and glucodynamic response to a standardized liquid meal (80 g of carbohydrate) in 21 patients with T2DM who received subcutaneous injections of individually optimized doses of lispro±rHuPH20 and RHI+rHuPH20. The optimum dose (targeting postprandial glucose [PPG] of 70-140 mg/dL) of each preparation was selected by the investigator following a fixed-dose escalation procedure in three dose-finding meals.

RESULTS

Co-injection of lispro+rHuPH20 accelerated pharmacokinetics relative to lispro alone (time to peak insulin concentration, 43 vs. 74 min; P=0.0045) with increased exposure in the first hour (184% of control; P<0.0001) and reduced exposure after 2 h (67% of control; P=0.0001). These accelerated pharmacokinetics improved both total hyperglycemic excursions (area under the curve for 0-4 h >140 mg/dL, 56% of control; P=0.048) and hypoglycemic excursions (area under the curve for 0-8 h <70 mg/dL, 34% of control; P=0.033), allowing over three times as many patients to reach the American Diabetes Association's target of peak PPG <180 mg/dL without requiring glucose treatment for hypoglycemia. The mean optimum dose of lispro was reduced 8% from 0.275 U/kg without rHuPH20 to 0.254 U/kg with rHuPH20 (P=0.04). RHI+rHuPH20 had responses and optimum doses comparable to insulin lispro alone. All insulin preparations were well tolerated.

CONCLUSIONS

Lispro+rHuPH20 provided superior control of glycemic excursion compared with lispro alone, with lower insulin requirements and reduced hypoglycemic excursions.

Reduction in intrasubject variability in the pharmacokinetic response to insulin after subcutaneous co-administration with recombinant human hyaluronidase in healthy volunteers

BACKGROUND

This study was designed to test the hypothesis that co-administration of recombinant human hyaluronidase (rHuPH20) with regular insulin or insulin lispro will reduce intrasubject variability in pharmacokinetic end points compared with lispro alone.

METHODS

Healthy adult volunteers (18-55 years old) were enrolled in this phase 1, randomized, double-blind, crossover study. Subjects were administered two injections, each on a separate occasion, of three treatments during six euglycemic clamps. Treatments were 0.15 U/kg insulin lispro, 0.15 U/kg insulin lispro with 5 μg/mL rHuPH20, and 0.15 IU/kg regular insulin with 5 μg/mL rHuPH20. Insulin formulations were administered at a concentration of 40 U/mL. Serum immunoreactive insulin levels, blood glucose concentration, and glucose infusion rate determinations were made at baseline and for approximately 8 h after study drug administration. Intrasubject variability was assessed using a general linear mixed model with a fixed effect for treatment using a compound symmetric covariance matrix.

RESULTS

Co-injection of rHuPH20 with lispro significantly reduced intrasubject root mean square differences in time to peak serum insulin, time to early 50% peak serum insulin (t(50%)), and time to late t(50%) levels compared with lispro alone. Also, the intrasubject coefficient of variation for percentage of total area under the plasma concentration-versus-time curve for early time intervals compared with lispro alone was reduced. Intrasubject variability for regular insulin with rHuPH20 for most pharmacokinetic parameters was similar to the variability of lispro alone, although variability in early exposure was significantly reduced.

CONCLUSIONS

Co-administration of rHuPH20 with lispro significantly reduced the variability of insulin pharmacokinetics relative to insulin lispro alone.

A review of modern insulin analogue pharmacokinetic and pharmacodynamic profiles in type 2 diabetes: improvements and limitations

Insulin analogues have been engineered to enhance desired molecular properties without altering immunogenicity. The majority of insulin pharmacology studies are conducted in healthy volunteers and patients with type 1 diabetes. At present, there are more patients with type 2 than type 1 diabetes receiving insulin treatment. As the responsibility for initiating insulin therapy in these patients continues to shift to primary care, it will be important for general practitioners to understand the different pharmacological properties of insulin preparations in patients with type 2 diabetes, so that treatment can be adapted to meet patients' physiological and lifestyle requirements. The purpose of this review is to summarize pharmacological studies of insulin analogues in patients with type 2 diabetes. Faster onset of action of rapid acting insulin analogues has improved postprandial glycaemic control. Biphasic insulin analogues are associated with a lower incidence of nocturnal hypoglycaemia compared with human biphasic preparations and allow for intensification from once to twice or thrice daily dosing. More predictable glycaemic-lowering profiles of the insulin analogues have also led to reductions in nocturnal hypoglycaemia, particularly comparing long-acting insulin analogues with protaminated human insulin. Enhancing insulin self-association and reversible binding with albumin has led to further reductions in variability. However, improvements can still be made. Effective once daily clinical dosing of long-acting insulin analogues is not possible in all patients. In addition, the protaminated component of biphasic insulin analogues do not provide the duration of action or profile for physiological basal insulin replacement and neither insulin glargine nor insulin detemir are suitable for mixing with other insulin analogues as this would substantially alter their pharmacokinetic properties. Enhancing the pharmacological predictability and extending the duration of action could simplify insulin titration and further reduce the incidence of hypoglycaemia.