Self-assembling peptides improve the stability of glucagon-like peptide-1 by forming a stable and sustained complex

Computational Peptide Design Cotargeting Glucagon and Glucagon-like Peptide-1 Receptors

Peptides are sustainable alternatives to conventional therapeutics for G protein-coupled receptor (GPCR) linked disorders, promising biocompatible and tailorable next-generation therapeutics for metabolic disorders including type-2 diabetes, as agonists of the glucagon receptor (GCGR) and the glucagon-like peptide-1 receptor (GLP-1R). However, single agonist peptides activating GLP-1R to stimulate insulin secretion also suppress obesity-linked glucagon release. Hence, bioactive peptides cotargeting GCGR and GLP-1R may remediate the blood glucose and fatty acid metabolism imbalance, tackling both diabetes and obesity to supersede current monoagonist therapy. Here, we design and model optimized peptide sequences starting from peptide sequences derived from earlier phage-displayed library screening, identifying those with predicted molecular binding profiles for dual agonism of GCGR and GLP-1R. We derive design rules from extensive molecular dynamics simulations based on peptide-receptor binding. Our newly designed coagonist peptide exhibits improved predicted coupled binding affinity for GCGR and GLP-1R relative to endogenous ligands and could in the future be tested experimentally, which may provide superior glycemic and weight loss control.

Developing GLP-1 Conjugated Self-Assembling Nanofibers Using Copper-Catalyzed Alkyne-Azide Cycloaddition and Evaluation of Their Biological Activity

Glucagon-like peptide-1 GLP-1 is a gut-derived peptide secreted from pancreatic β-cells that reduces blood glucose levels and body weight; however, native GLP-1 (GLP-1(7-36)-NH₂ and GLP-1(7-37)) have short in vivo circulation half-lives (∼2 min) due to proteolytic degradation and rapid renal clearance due to its low molecular weight (MW; 3297.7 Da). This study aimed to improve the proteolytic stability and delivery properties of glucagon-like peptide-1 (GLP-1) through modifications that form nanostructures. For this purpose, N- (NtG) and C-terminal (CtG), and Lys26 side chain (K26G) alkyne-modified GLP-1 analogues were conjugated to an azide-modified lipidic peptide (L) to give N-L, C-L, and K-26-L, respectively; or CtG was conjugated with a fibrilizing self-assembling peptide (SAP) (AEAEAKAK)₃ to yield C-S, using copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC). N-L demonstrated the best serum stability (t_1/2 > 48 h) compared to K-26-L (44 h), C-L (20 h), C-S (27 h), and the parental GLP-1(7-36;A8G)-NH₂ (A8G) (19 h) peptides. Each conjugate demonstrated subnanomolar hGLP-1RA potency, and none demonstrated toxicity toward PC-3 cells at concentrations up to 1 μM. Each analogue was observed by transmission electron microscopy to form fibrils in solution. K-26-L demonstrated among the best human serum stability (t_1/2 = 44 h) and similar hGLP-1RA potency (EC₅₀ 48 pM) to C-S. In conclusion, this study provided an alternative to lipid modification, i.e., fibrillizing peptides, that could improve pharmacokinetic parameters of GLP-1.

Self-Assembly of Lipopeptides Containing Short Peptide Fragments Derived from the Gastrointestinal Hormone PYY3-36: From Micelles to Amyloid Fibrils

We investigate the impact of lipidation on the self-assembly of two peptide fragments from the gastrointestinal peptide hormone PYY_3–36. The lipopeptides C₁₆IKPEAP and C₁₆IKPEAPGE contain the first 6 and 8 amino acid residues, respectively, from the PYY_3–36 peptide sequence, with a palmitoyl C₁₆ tail attached at the N-terminus. These lipopeptides form spherical micelles in aqueous solution, above a critical micelle concentration (cmc), which is pH-dependent. Modeling of small-angle X-ray scattering data along with molecular dynamics simulations shows the formation of micelles with a hydrophobic interior and a well-hydrated exterior. The lipopeptides have a disordered conformation over the pH and temperature ranges studied. The cmc is found to be independent of temperature, pointing to athermal micellization. In contrast to the presence of hydrated micelles in solution, β-sheet amyloid fibrils form in dried samples. Thus, the nanostructure of lipidated PYY_3–36 fragment peptides can be tuned by control of pH or concentration, for future applications.

Effects of the multilayer structures on Exenatide release and bioactivity in microsphere/thermosensitive hydrogel system

Traditional polypeptide-loaded PLGA microspheres (PM) using emulsion electrospray techniques often exhibit unsteady release and limited bioactivity. To solve these two problems, an Exenatide (EXT)-loaded multilayer system composed ofPM and thermosensitive hydrogel was prepared by the emulsion electrospray technique in this study. Hydrogel mixture were loaded in PLGA microspheres as Depot-hydrogel to prepare Gel/PM. The PM/Gel and Gel/PM/Gel systems were obtained by dispersion of PM and Gel/PM into hydrogel mixture, respectively. EXT in Gel/PM/Gel showed a constantly in vitro release for 30 days, which was significantly enhanced in comparison of those in the PM/Gel and the Gel/PM. PM/Gel and Gel/PM/Gel showed diminished burst release and no platform period compared with PM and Gel/PM. And these could be because the introduced Matrix-hydrogel outside, as a buffer layer, inhibited burst releases and exhibited a sustained manner. The inner Depot-hydrogelstructure slowed the PLGA degradation rate and drug release rate. As well, more than 15-day blood glucose levels in KKAy mice were greatly maintained at 7.50-9.50 mmol/L after a single subcutaneous injection of Gel/PM/Gel (4.95 μg/kg). Spatial stability and further bioactivity of released EXT were well protected by EXT-hydrogel complexes, and undesirable uptake of EXT and microspheres via phagocytes were also decreased by PEG shell. Thus, the long-acting microspheres/hydrogel multilayer system prepared by emulsion electrospray technique showed promising potentials for loading hydrophilic polypeptides and proteins.

Peptide hormones and lipopeptides: from self-assembly to therapeutic applications

This review describes the properties and activities of lipopeptides and peptide hormones and how the lipidation of peptide hormones could potentially produce therapeutic agents combating some of the most prevalent diseases and conditions. The self‐assembly of these types of molecules is outlined, and how this can impact on bioactivity. Peptide hormones specific to the uptake of food and produced in the gastrointestinal tract are discussed in detail. The advantages of lipidated peptide hormones over natural peptide hormones are summarised, in terms of stability and renal clearance, with potential application as therapeutic agents. © 2017 The Authors Journal of Peptide Science published by European Peptide Society and John Wiley & Sons Ltd.

Oligomerization of a Glucagon-like Peptide 1 Analog: Bridging Experiment and Simulations

The glucagon-like peptide 1 (GLP-1) analog, liraglutide, is a GLP-1 agonist and is used in the treatment of type-2 diabetes mellitus and obesity. From a pharmaceutical perspective, it is important to know the oligomerization state of liraglutide with respect to stability. Compared to GLP-1, liraglutide has an added fatty acid (FA) moiety that causes oligomerization of liraglutide as suggested by small-angle x-ray scattering (SAXS) and multiangle static light scattering (MALS) results. SAXS data suggested a global shape of a hollow elliptical cylinder of size hexa-, hepta-, or octamer, whereas MALS data indicate a hexamer. To elaborate further on the stability of these oligomers and the role of the FA chains, a series of molecular-dynamics simulations were carried out on 11 different hexa-, hepta-, and octameric systems. Our results indicate that interactions of the fatty acid chains contribute noticeably to the stabilization. The simulation results indicate that the heptamer with paired FA chains is the most stable oligomer when compared to the 10 other investigated structures. Theoretical SAXS curves extracted from the simulations qualitatively agree with the experimentally determined SAXS curves supporting the view that liraglutide forms heptamers in solution. In agreement with the SAXS data, the heptamer forms a water-filled oligomer of elliptical cylindrical shape.

Transformation of oligomers of lipidated peptide induced by change in pH

Oligomerization of lipidated peptides is of general scientific interest and is important in biomedical and pharmaceutical applications. We investigated the solution properties of a lipidated peptide, Liraglutide, which is one of the glucagon-like peptide-1 (GLP-1) agonists used for the treatment of type II diabetes. Liraglutide can serve as a model system for studying biophysical and biochemical properties of micelle-like self-assemblies of the lipidated peptides. Here, we report a transformation induced in Liraglutide oligomers by changing pH in the vicinity of pH 7. This fully reversible transformation is characterized by changes in the size and aggregation number of the oligomer and an associated change in the secondary structure of the constituent peptides. This transformation has quite slow kinetics: the equilibrium is reached in a course of several days. Interestingly, while the transformation is induced by changing pH, its kinetics is essentially independent of the final pH. We interpreted these findings using a model in which desorption of the monomer from the oligomer is the rate-limiting step in the transformation, and we determined the rate constant of the monomer desorption.

Molecular dynamics study of surfactant-like peptide based nanostructures

Surfactant-like peptide (SLP) based nanostructures are investigated using all-atomistic molecular dynamics (MD) simulations. We report structure properties of nanostructures belonging to the ANK peptide group. In particular, the mathematical models for the two A3K membranes, A6K nanotube, and A9K nanorod were developed. Our MD simulation results are consistent with the experimental data, indicating that A3K membranes are stable in two different configurations: (1) SLPs are tilted relative to the normal membrane plane; (2) SLPs are interdigitated. The former configuration is energetically more stable. The cylindrical nanostructures feature a certain order of the A6K peptides. In turn, the A9K nanorod does not exhibit any long-range ordering. Both nanotube and nanorod structure contain large amounts of water inside. Consequently, these nanostructures behave similar to hydrogels. This property may be important in the context of biotechnology. Binding energy analysis-in terms of Coulomb and van der Waals contributions-unveils an increase as the peptide size increases. The electrostatic interaction constitutes 70-75% of the noncovalent attraction energy between SLPs. The nanotubular structures are notably stable, confirming that A6K peptides preferentially form nanotubes and A9K peptides preferentially form nanorods.