A novel, stable, aqueous glucagon formulation using ferulic acid as an excipient

Computational and Experimental Evaluation of the Stability of a GLP-1-like Peptide in Ethanol–Water Mixtures

Aggregation resulting from the self-association of peptide molecules remains a major challenge during preformulation. Whereas certain organic solvents are known to promote aggregation, ethanol (EtOH) is capable of disrupting interactions between peptide molecules. It is unclear whether it is beneficial or counterproductive to include EtOH in formulations of short peptides. Here, we employed molecular dynamics simulations using the DAFT protocol and MARTINI force field to predict the formation of self-associated dimers and to estimate the stability of a GLP-1-like peptide (G48) in 0–80% aqueous EtOH solutions. Both simulation and experimental data reveal that EtOH leads to a remarkable increase in the conformational stability of the peptide when stored over 15 days at 27 °C. In the absence of EtOH, dimerisation and subsequent loss in conformational stability (α-helix → random coil) were observed. EtOH improved conformational stability by reducing peptide–peptide interactions. The data suggest that a more nuanced approach may be applied in formulation decision making and, if the native state of the peptide is an α-helix organic solvent, such as EtOH, may enhance stability and improve prospects of long-term storage.

'Smart' insulin-delivery technologies and intrinsic glucose-responsive insulin analogues

Insulin replacement therapy for diabetes mellitus seeks to minimise excursions in blood glucose concentration above or below the therapeutic range (hyper- or hypoglycaemia). To mitigate acute and chronic risks of such excursions, glucose-responsive insulin-delivery technologies have long been sought for clinical application in type 1 and long-standing type 2 diabetes mellitus. Such 'smart' systems or insulin analogues seek to provide hormonal activity proportional to blood glucose levels without external monitoring. This review highlights three broad strategies to co-optimise mean glycaemic control and time in range: (1) coupling of continuous glucose monitoring (CGM) to delivery devices (algorithm-based 'closed-loop' systems); (2) glucose-responsive polymer encapsulation of insulin; and (3) mechanism-based hormone modifications. Innovations span control algorithms for CGM-based insulin-delivery systems, glucose-responsive polymer matrices, bio-inspired design based on insulin's conformational switch mechanism upon insulin receptor engagement, and glucose-responsive modifications of new insulin analogues. In each case, innovations in insulin chemistry and formulation may enhance clinical outcomes. Prospects are discussed for intrinsic glucose-responsive insulin analogues containing a reversible switch (regulating bioavailability or conformation) that can be activated by glucose at high concentrations.

Inhibiting the fibrillation of a GLP-1-like peptide

Aggregation, including the formation of fibrils, poses significant challenges for the development of therapeutic peptides. To prepare stable peptide formulations, some understanding of the mechanisms underpinning the fibrillation process is required. A thioflavin T fluorescence assay was first used to determine the fibrillation profile of a GLP-1-like peptide (G48) at conditions being considered to formulate the peptide. G48 concentrations ranged from 0 to 600 µM and three pH values (pH 3.7, 7.4 and 8.5) were evaluated. Kinetic data demonstrate that G48 displays a pH-dependent aggregation profile. At pH 3.7, which is below the isoelectric point of G48 (pI ~ 5), kinetics representative of amorphous aggregates forming via a nucleation-independent mechanism were seen. At pH 7.4 and 8.5 (pH > pI) typical nucleation-dependent aggregation kinetics were observed. The weight concentration of β-sheet rich aggregates (FL_max) correlated inversely with net charge, so lower FL_max values were observed at pH 3.7 and 8.5 than at pH 7.4. Incorporation of a non-ionic surfactant (polysorbate 80) into the peptide solution suppressed the fibrillation of G48 at all pH values and maintained the native peptide conformation, whereas a phenolic co-formulant (ferulic acid) had minimal effects on fibril growth. Peptide fibrillation, which can occur within a range of formulation concentrations and pH values, can hence be inhibited by the judicious use of excipients.

Artificial Pancreas or Novel Beta-Cell Replacement Therapies: a Race for Optimal Glycemic Control?

PURPOSE OF REVIEW

New treatment strategies are needed for patients with type 1 diabetes (T1D). Closed loop insulin delivery and beta-cell replacement therapy are promising new strategies. This review aims to give an insight in the most relevant literature on this topic and to compare the two radically different treatment modalities.

RECENT FINDINGS

Multiple clinical studies have been performed with closed loop insulin delivery devices and have shown an improvement in overall glycemic control and time spent in hypoglycemia. Beta-cell transplantation has been shown to normalize or greatly improve glycemic control in T1D, but the donor organ shortage and the necessity to use immunosuppressive agents are major drawbacks. Donor organ shortage may be solved by the utilization of stem cell-derived beta cells, which has shown great promise in animal models and are now tested in clinical studies. Immunosuppression may be avoided by encapsulation. Closed loop insulin delivery devices are promising treatment strategies and are likely to be used in clinical practice in the short term. But this approach will always suffer from delays in glucose measurement and insulin action preventing it from normalizing glycemic control. In the long term, stem cell-derived beta cell transplantation may be able to achieve this, but wide implementation in clinical practice is still far away.

Stable Liquid Glucagon: Beyond Emergency Hypoglycemia Rescue

Glycemic control is the mainstay of preventing diabetes complications at the expense of increased risk of hypoglycemia. Severe hypoglycemia negatively impacts the quality of life of patients with type 1 diabetes and can lead to morbidity and mortality. Currently available glucagon emergency kits are effective at treating hypoglycemia when correctly used, however use is complicated especially by untrained persons. Better formulations and devices for glucagon treatment of hypoglycemia are needed, specifically stable liquid glucagon. Out of the scope of this review, other potential uses of stable liquid glucagon include congenital hyperinsulinism, post-bariatric surgery hypoglycemia, and insulinoma induced hypoglycemia. In the 35 years since Food and Drug Administration (FDA) approval of the first liquid stable human recombinant insulin, we continue to wait for the glucagon counterpart. For mild hypoglycemia, a commercially available liquid stable glucagon would enable more widespread implementation of mini-dose glucagon use as well as glucagon in dual hormone closed-loop systems. This review focuses on the current and upcoming pharmaceutical uses of glucagon in the treatment of type 1 diabetes with an outlook on stable liquid glucagon preparations that will hopefully be available for use in patients in the near future.

Current status and issues of the artificial pancreas: abridged English translation of a special issue in Japanese

Surgical stress induces hyperglycemia and gives rise to glucose toxicity, which causes infectious diseases, resulting in unfavorable surgical outcomes. Intensive insulin treatment can control short- and long-term complications in patients with not only diabetes mellitus, but also surgical diabetes; however, it is associated with an increased risk of hypoglycemia. The wearable artificial pancreas was originally developed to control glucose levels in patients with type 1 diabetes, progressing to a device with enhanced stability and safety for these patients. Its usability has further progressed to include patients with type 2 diabetes. The bedside artificial pancreas is the only closed-loop-type artificial pancreas which can maintain stable glycemic control in accordance with a target blood glucose range, based on the patient's actual blood glucose levels. Moreover, this stable glycemic control with a low variation in blood glucose concentration within the target range is produced without any hypoglycemia. Significant advances of this device will now occur due to the approval of treatment for perioperative glycemic control by the Japanese Health Care Insurance System in 2016. Along with an increase in the number of mainly elderly patients with low glucose tolerance, it is expected that the role of the artificial pancreas will increase in the future. Considering the current state and expense of regenerative and transplant medicine, along with donor shortages, further development of the artificial pancreas and associated glycemic control can be expected.

Stability of Commercially Available Glucagon Formulation for Dual-Hormone Artificial Pancreas Clinical Use

BACKGROUND

Available glucagon formulations are approved for immediate use after reconstitution for severe hypoglycemia emergency treatment. However, they are used in dual-hormone artificial pancreas (insulin and glucagon) studies through subcutaneous infusion pumps over 24 h. Chemical and physical stability of such glucagon use have not been reported in a comprehensive manner.

MATERIALS AND METHODS

Recombinant Glucagon DNA (Eli Lilly) was used. Compatibility and sterility of glucagon delivery through subcutaneous pump systems were verified. Glucagon degradation through liquid chromatography with tandem mass spectrometry (LC-MS/MS), fibrillation using intrinsic tryptophan fluorescence shift, and bioactivity through a cell-protein kinase A-based fluorescent bioassay were assessed over a range of different physical conditions (temperature, movement, and air bubbles).

RESULTS

Subcutaneous infusion pump systems administered glucagon in sterile conditions and with comparable accuracy to insulin delivery; mean absolute relative difference of actual versus expected weights were 1.2% ± 1.1% for glucagon and 1.1% ± 0.5% for insulin (P = 0.9). In comparison to freshly reconstituted samples, glucagon analyzed through LC-MS/MS was intact at 93.0% ± 7.0% after 24 h (P = 0.42) and 83.04% ± 6.0% after 48 h (P = 0.02) of incubation in pumps at 32°C. Peak wavelengths for Trp fluorescence did not differ from samples exposed to air bubbles or movement whether incubated (in infusion sets for 24 h at 32°) immediately or 24- and 48-h poststorage at 4°C (P = 0.10, 0.70 and 0.80, respectively) and no significant differences in bioactivity (shifts in EC₅₀) were found for the same conditions (P = 0.13, 0.83, and 0.63).

CONCLUSION

Available glucagon formulations are chemically and physically stable, as well as compatible with delivery through subcutaneous infusion pumps over 24 h and can be used in long-term clinical trials.

Development of glucose-responsive 'smart' insulin systems

PURPOSE OF REVIEW

The complexity of modern insulin-based therapy for type I and type II diabetes mellitus and the risks associated with excursions in blood-glucose concentration (hyperglycemia and hypoglycemia) have motivated the development of 'smart insulin' technologies (glucose-responsive insulin, GRI). Such analogs or delivery systems are entities that provide insulin activity proportional to the glycemic state of the patient without external monitoring by the patient or healthcare provider. The present review describes the relevant historical background to modern GRI technologies and highlights three distinct approaches: coupling of continuous glucose monitoring (CGM) to deliver devices (algorithm-based 'closed-loop' systems), glucose-responsive polymer encapsulation of insulin, and molecular modification of insulin itself.

RECENT FINDINGS

Recent advances in GRI research utilizing each of the three approaches are illustrated; these include newly developed algorithms for CGM-based insulin delivery systems, glucose-sensitive modifications of existing clinical analogs, newly developed hypoxia-sensitive polymer matrices, and polymer-encapsulated, stem-cell-derived pancreatic β cells.

SUMMARY

Although GRI technologies have yet to be perfected, the recent advances across several scientific disciplines that are described in this review have provided a path towards their clinical implementation.

Moving Toward a Unified Platform for Insulin Delivery and Sensing of Inputs Relevant to an Artificial Pancreas

Advances in insulin pump and continuous glucose monitoring technology have primarily focused on optimizing glycemic control for people with type 1 diabetes. There remains a need to identify ways to minimize the physical burden of this technology. A unified platform with closely positioned or colocalized interstitial fluid glucose sensing and hormone delivery components is a potential solution. Present challenges to combining these components are interference of glucose sensing from proximate insulin delivery and the large discrepancy between the life span of current insulin infusion sets and glucose sensors. Addressing these concerns is of importance given that the future physical burden of this technology is likely to be even greater with the ongoing development of the artificial pancreas, potentially incorporating multiple hormone delivery, glucose sensing redundancy, and sensing of other clinically relevant nonglucose biochemical inputs.

Glucagon in artificial pancreas systems: Potential benefits and safety profile of future chronic use

The role of glucagon in the pathophysiology of diabetes has long been recognized, although its approved clinical use has so far been limited to the emergency treatment of severe hypoglycaemia. A novel use of glucagon as intermittent mini-boluses is proposed in the dual-hormone version (insulin and glucagon) of the external artificial pancreas. Short-term studies suggest that the incorporation of glucagon into artificial pancreas systems has the potential to further decrease hypoglycaemic risk and improve overall glucose control; however, the potential long-term safety and benefits also need to be investigated given the recognized systemic effects of glucagon. In the present report, we review the available animal and human data on the physiological functions of glucagon, as well as its pharmacological use, according to dosing and duration (acute and chronic). Along with its main role in hepatic glucose metabolism, glucagon affects the cardiovascular, renal, pulmonary and gastrointestinal systems. It has a potential role in weight reduction through its central satiety function and its role in increasing energy expenditure. Most of the pharmacological studies investigating the effects of glucagon have used doses exceeding 1 mg, in contrast to the mini-boluses used in the artificial pancreas. The available data are reassuring but comprehensive human studies using small but chronic glucagon doses that are close to the physiological ranges are lacking. We propose a list of variables that could be monitored during long-term trials of the artificial pancreas. Such trials should address the questions about the risk-benefit ratio of chronic glucagon use.

Native Design of Soluble, Aggregation-Resistant Bioactive Peptides: Chemical Evolution of Human Glucagon

Peptide-based therapeutics commonly suffer from biophysical properties that compromise pharmacology and medicinal use. Structural optimization of the primary sequence is the usual route to address such challenges while trying to maintain as much native character and avoiding introduction of any foreign element that might evoke an immunological response. Glucagon serves a seminal physiological role in buffering against hypoglycemia, but its low aqueous solubility, chemical instability, and propensity to self-aggregate severely complicate its medicinal use. Selective amide bond replacement with metastable ester bonds is a preferred approach to the preparation of peptides with biophysical properties that otherwise inhibit synthesis. We have recruited such chemistry in the design and development of unique glucagon prodrugs that have physical properties suitable for medicinal use and yet rapidly convert to native hormone upon exposure to slightly alkaline pH. These prodrugs demonstrate in vitro and in vivo pharmacology when formulated in physiological buffers that are nearly identical to native hormone when solubilized in conventional dilute hydrochloric acid. This approach provides the best of both worlds, where the pro-drug delivers chemical properties supportive of aqueous formulation and the native biological properties.

Pyridyl-alanine as a Hydrophilic, Aromatic Element in Peptide Structural Optimization

Glucagon (Gcg) 1 serves a seminal physiological role in buffering against hypoglycemia, but its poor biophysical properties severely complicate its medicinal use. We report a series of novel glucagon analogues of enhanced aqueous solubility and stability at neutral pH, anchored by Gcg[Aib16]. Incorporation of 3- and 4-pyridyl-alanine (3-Pal and 4-Pal) enhanced aqueous solubility of glucagon while maintaining biological properties. Relative to native hormone, analogue 9 (Gcg[3-Pal6,10,13, Aib16]) demonstrated superior biophysical character, better suitability for medicinal purposes, and comparable pharmacology against insulin-induced hypoglycemia in rats and pigs. Our data indicate that Pal is a versatile surrogate to natural aromatic amino acids and can be employed as an alternative or supplement with isoelectric adjustment to refine the biophysical character of peptide drug candidates.

Effect of Repeated Glucagon Doses on Hepatic Glycogen in Type 1 Diabetes: Implications for a Bihormonal Closed-Loop System

OBJECTIVE

To evaluate subjects with type 1 diabetes for hepatic glycogen depletion after repeated doses of glucagon, simulating delivery in a bihormonal closed-loop system.

RESEARCH DESIGN AND METHODS

Eleven adult subjects with type 1 diabetes participated. Subjects underwent estimation of hepatic glycogen using (13)C MRS. MRS was performed at the following four time points: fasting and after a meal at baseline, and fasting and after a meal after eight doses of subcutaneously administered glucagon at a dose of 2 µg/kg, for a total mean dose of 1,126 µg over 16 h. The primary and secondary end points were, respectively, estimated hepatic glycogen by MRS and incremental area under the glucose curve for a 90-min interval after glucagon administration.

RESULTS

In the eight subjects with complete data sets, estimated glycogen stores were similar at baseline and after repeated glucagon doses. In the fasting state, glycogen averaged 21 ± 3 g/L before glucagon administration and 25 ± 4 g/L after glucagon administration (mean ± SEM) (P = NS). In the fed state, glycogen averaged 40 ± 2 g/L before glucagon administration and 34 ± 4 g/L after glucagon administration (P = NS). With the use of an insulin action model, the rise in glucose after the last dose of glucagon was comparable to the rise after the first dose, as measured by the 90-min incremental area under the glucose curve.

CONCLUSIONS

In adult subjects with well-controlled type 1 diabetes (mean A1C 7.2%), glycogen stores and the hyperglycemic response to glucagon administration are maintained even after receiving multiple doses of glucagon. This finding supports the safety of repeated glucagon delivery in the setting of a bihormonal closed-loop system.

Glucagon - the new 'insulin' in the pathophysiology of diabetes

PURPOSE OF REVIEW

Autoimmune destruction of the β cells is considered the key abnormality in type 1 diabetes mellitus and insulin replacement the primary therapeutic strategy. However, a lack of insulin is accompanied by disturbances in glucagon release, which is excessive postprandially, but insufficient during hypoglycaemia. In addition, replacing insulin alone appears insufficient for adequate glucose control. This review focuses on the growing body of evidence that glucagon abnormalities contribute significantly to the pathophysiology of diabetes and on recent efforts to target the glucagon axis as adjunctive therapy to insulin replacement.

RECENT FINDINGS

This review discusses recent (since 2013) advances in abnormalities of glucagon regulation and their link to the pathophysiology of diabetes; new mechanisms of glucagon action and regulation; manipulation of glucagon in diabetes treatment; and analytical and systems biology tools to study glucagon regulation.

SUMMARY

Recent efforts 'resurrected' glucagon as a key hormone in the pathophysiology of diabetes. New studies target its abnormal regulation and action that is key for improving diabetes treatment. The progress is promising, but major questions remain, including unravelling the mechanism of loss of glucagon counterregulation in type 1 diabetes mellitus and how best to manipulate glucagon to achieve more efficient and safer glycaemic control.