Assembly of a Tripeptide and Anti-Inflammatory Drugs into Supramolecular Hydrogels for Sustained Release

Enhancing the stability of natural anthocyanins against environmental stressors through encapsulation with synthetic peptide-based gels

The instability of anthocyanin to environmental stressors severely limits its applications as a natural bioactive pigment. To overcome these limitations, this proof-of-concept study utilizes the high biocompatibility of peptide molecules and the unique gel microstructure to develop innovative peptide-based gels. Characterization of the gels was conducted through AFM, SEM, rheological analysis, and CD spectrum. These analyses confirmed the fibrous mesh structure and impressive mechanical strength of the peptide-based gels. The cytotoxicity evaluation using MTT and hemolysis analysis showed high biocompatibility. Encapsulation efficiency analysis and fluorescence microscopy images demonstrated successful and efficient encapsulation of anthocyanins in all four peptide-based gels, with uniform distribution. Moreover, systematic investigations were conducted to assess the impact of peptide-based gels on the stability of natural anthocyanins under environmental stressors such as temperature, pH variations, and exposure to metal ions. Notably, the results revealed a significant enhancement in stability, including improved long-term storage and antioxidant activity. In conclusion, this study successfully developed four novel peptide-based gels that effectively protect natural anthocyanins from environmental stressors, highlighting their potential in various fields such as food and biology.

Self-assembling tripeptide forming water-bound channels and hydrogels

D-Ser(tBu)-L-Phe-L-Trp is described as a self-assembling tripeptide that yields nanofibrillar hydrogels at physiological conditions (phosphate buffer at pH 7.4). The peptide is characterized by several spectroscopic methods, such as circular dichroism and fluorescence, oscillatory rheometry, and transmission electron microscopy. Single-crystal X-ray diffraction reveals supramolecular packing into water-bound channels and allows the visualization of the intermolecular interactions holding together peptide stacks.

Self-Assembly of Homo- and Hetero-Chiral Cyclodipeptides into Supramolecular Polymers towards Antimicrobial Gels

There is an increasing interest towards the development of new antimicrobial coatings, especially in light of the emergence of antimicrobial resistance (AMR) towards common antibiotics. Cyclodipeptides (CDPs) or diketopiperazines (DKPs) are attractive candidates for their ability to self-assemble into supramolecular polymers and yield gel coatings that do not persist in the environment. In this work, we compare the antimicrobial cyclo(Leu-Phe) with its heterochiral analogs cyclo(D-Leu-L-Phe) and cyclo(L-Leu-D-Phe), as well as cyclo(L-Phe-D-Phe), for their ability to gel. The compounds were synthesized, purified by HPLC, and characterized by ¹H-NMR, ¹³C-NMR, and ESI-MS. Single-crystal X-ray diffraction (XRD) revealed details of the intermolecular interactions within the supramolecular polymers. The DKPs were then tested for their cytocompatibility on fibroblast cells and for their antimicrobial activity on S. aureus. Overall, DKPs displayed good cytocompatibility and very mild antimicrobial activity, which requires improvement towards applications.

Controlling Doxorubicin Release from a Peptide Hydrogel through Fine-Tuning of Drug-Peptide Fiber Interactions

Hydrogels are versatile materials that have emerged in the last few decades as promising candidates for a range of applications in the biomedical field, from tissue engineering and regenerative medicine to controlled drug delivery. In the drug delivery field, in particular, they have been the subject of significant interest for the spatially and temporally controlled delivery of anticancer drugs and therapeutics. Self-assembling peptide-based hydrogels, in particular, have recently come to the fore as potential candidate vehicles for the delivery of a range of drugs. In order to explore how drug–peptide interactions influence doxorubicin (Dox) release, five β-sheet-forming self-assembling peptides with different physicochemical properties were used for the purpose of this study, namely: FEFKFEFK (F8), FKFEFKFK (FK), FEFEFKFE (FE), FEFKFEFKK (F8K), and KFEFKFEFKK (KF8K) (F: phenylalanine; E: glutamic acid; K: lysine). First, Dox-loaded hydrogels were characterized to ensure that the incorporation of the drug did not significantly affect the hydrogel properties. Subsequently, Dox diffusion out of the hydrogels was investigated using UV absorbance. The amount of drug retained in F8/FE composite hydrogels was found to be directly proportional to the amount of charge carried by the peptide fibers. When cation−π interactions were used, the position and number of end-lysine were found to play a key role in the retention of Dox. In this case, the amount of Dox retained in F8/KF8K composite hydrogels was linked to the amount of end-lysine introduced, and an end-lysine/Dox interaction stoichiometry of 3/1 was obtained. For pure FE and KF8K hydrogels, the maximum amount of Dox retained was also found to be related to the overall concentration of the hydrogels and, therefore, to the overall fiber surface area available for interaction with the drug. For 14 mM hydrogel, ∼170–200 μM Dox could be retained after 24 h. This set of peptides also showed a broad range of susceptibilities to enzymatic degradation opening the prospect of being able to control also the rate of degradation of these hydrogels. Finally, the Dox released from the hydrogel was shown to be active and affect 3T3 mouse fibroblasts viability in vitro. Our study clearly shows the potential of this peptide design as a platform for the formulation of injectable or sprayable hydrogels for controlled drug delivery.

Tuning the drug multimodal release through a co-assembly strategy based on magnetic gels

Self-assembled short peptide-based gels are highly promising drug delivery systems. However, implementing a stimulus often requires screening different structures to obtain gels with suitable properties, and drugs might not be well encapsulated and/or cause undesirable effects on the gel's properties. To overcome this challenge, a new design approach is presented to modulate the release of doxorubicin as a model chemotherapeutic drug through the interplay of (di)phenylalanine-coated magnetic nanoparticles, PEGylated liposomes and doxorubicin co-assembly in dehydropeptide-based gels. The composites enable an enhancement of the gelation kinetics in a concentration-dependent manner, mainly through the use of PEGylated liposomes. The effect of the co-assembly of phenylalanine-coated nanoparticles with the hydrogel displays a concentration and size dependence. Finally, the integration of liposomes as doxorubicin storage units and of nanoparticles as composites that co-assemble with the gel matrix enables the tuneability of both passive and active doxorubicin release through a thermal, and a low-frequency alternating magnetic field-based trigger. In addition to the modulation of the gel properties, the functionalization with (di)phenylalanine improves the cytocompatibility of the nanoparticles. Hereby, this work paves a way for the development of peptide-based supramolecular systems for on-demand and controlled release of drugs.

Smart Hydrogels Meet Carbon Nanomaterials for New Frontiers in Medicine

Carbon nanomaterials include diverse structures and morphologies, such as fullerenes, nano-onions, nanodots, nanodiamonds, nanohorns, nanotubes, and graphene-based materials. They have attracted great interest in medicine for their high innovative potential, owing to their unique electronic and mechanical properties. In this review, we describe the most recent advancements in their inclusion in hydrogels to yield smart systems that can respond to a variety of stimuli. In particular, we focus on graphene and carbon nanotubes, for applications that span from sensing and wearable electronics to drug delivery and tissue engineering.

Peptide-Protein Interactions: From Drug Design to Supramolecular Biomaterials

The self-recognition and self-assembly of biomolecules are spontaneous processes that occur in Nature and allow the formation of ordered structures, at the nanoscale or even at the macroscale, under thermodynamic and kinetic equilibrium as a consequence of specific and local interactions. In particular, peptides and peptidomimetics play an elected role, as they may allow a rational approach to elucidate biological mechanisms to develop new drugs, biomaterials, catalysts, or semiconductors. The forces that rule self-recognition and self-assembly processes are weak interactions, such as hydrogen bonding, electrostatic attractions, and van der Waals forces, and they underlie the formation of the secondary structure (e.g., α-helix, β-sheet, polyproline II helix), which plays a key role in all biological processes. Here, we present recent and significant examples whereby design was successfully applied to attain the desired structural motifs toward function. These studies are important to understand the main interactions ruling the biological processes and the onset of many pathologies. The types of secondary structure adopted by peptides during self-assembly have a fundamental importance not only on the type of nano- or macro-structure formed but also on the properties of biomaterials, such as the types of interaction, encapsulation, non-covalent interaction, or covalent interaction, which are ultimately useful for applications in drug delivery.

Self-Assembling, Ultrashort Peptide Gels as Antimicrobial Biomaterials

Supramolecular antimicrobial hydrogels based on peptides are attractive soft materials for the treatment of infections, considering their ease of preparation and benign fate in biological settings and in the environment. In particular, stimuli-responsive systems that can be assembled/disassembled ad hoc could offer the opportunity to switch on/off their bioactivity as needed. Besides, the shorter is the peptide, the lower its cost of production. However, a structure-to-function relationship is yet to be defined and reported activities are generally not yet competitive relative to traditional antibiotics. Inspiration for their design can be found in host defense peptides (HDPs), which can self-assemble to exert their function. This article reviews research developments in this emerging area, and it examines features, differences and similarities between antimicrobial and amyloid peptides to open the avenue towards the next generation of supramolecular antimicrobial peptides as innovative therapeutic materials.

Impact of gelation method on thixotropic properties of phenylalanine-derived supramolecular hydrogels

Supramolecular hydrogels formed by noncovalent self-assembly of low molecular weight (LMW) agents are promising next-generation biomaterials. Thixotropic shear response and mechanical stability are two emergent properties of hydrogels that are critical for biomedical applications including drug delivery and tissue engineering in which injection of the hydrogel will be necessary. Herein, we demonstrate that the emergent thixotropic properties of supramolecular phenylalanine-derived hydrogels are dependent on the conditions in which they are formulated. Specifically, hydrogels formed from fluorenylmethoxycarbonyl (Fmoc) modified phenylalanine derivatives, 3-fluorophenylalanine (Fmoc-3F-Phe) and pentafluorophenylalanine (Fmoc-F5-Phe), were characterized as a function of gelation conditions to examine how shear response and mechanical stability properties correlate to mode of gelation. Two distinct methods of gelation were compared. First, spontaneous self-assembly and gelation was triggered by a solvent exchange method in which a concentrated solution of the gelator in dimethylsulfoxide was diluted in water. Second, gelation was promoted by dissolution of the gelator in water at basic pH followed by gradual pH adjustment from basic to mildly acidic by the hydrolysis of glucono-delta-lactone. Hydrogels formed under solvent exchange conditions were mechanically unstable and poorly shear-responsive whereas hydrogels formed by gradual acidification were temporally stable and had highly shear-responsive viscoelastic character. These studies confirm that gelation environment and mechanism have a significant influence on the emergent properties of supramolecular hydrogels and offer insight into how gelation conditions can be used to tune hydrogel properties for specific applications.

Ultrashort Peptide Self-Assembly: Front-Runners to Transport Drug and Gene Cargos

The translational therapies to promote interaction between cell and signal come with stringent eligibility criteria. The chemically defined, hierarchically organized, and simpler yet blessed with robust intermolecular association, the peptides, are privileged to make the cut-off for sensing the cell-signal for biologics delivery and tissue engineering. The signature service and insoluble network formation of the peptide self-assemblies as hydrogels have drawn a spell of research activity among the scientists all around the globe in the past decades. The therapeutic peptide market players are anticipating promising growth opportunities due to the ample technological advancements in this field. The presence of the other organic moieties, enzyme substrates and well-established protecting groups like Fmoc and Boc etc., bring the best of both worlds. Since the large sequences of peptides severely limit the purification and their isolation, this article reviews the account of last 5 years' efforts on novel approaches for formulation and development of single molecule amino acids, ultra-short peptide self-assemblies (di- and tri- peptides only) and their derivatives as drug/gene carriers and tissue-engineering systems.

Biological Evaluation of Naproxen-Dehydrodipeptide Conjugates with Self-Hydrogelation Capacity as Dual LOX/COX Inhibitors

The use of peptide-drug conjugates is emerging as a powerful strategy for targeted drug delivery. Previously, we have found that peptides conjugated to a non-steroidal anti-inflammatory drug (NSAID), more specifically naproxen-dehydrodipeptide conjugates, readily form nanostructured fibrilar supramolecular hydrogels. These hydrogels were revealed as efficacious nano-carriers for drug delivery applications. Moreover, the incorporation of superparamagnetic iron oxide nanoparticles (SPIONs) rendered the hydrogels responsive to external magnetic fields, undergoing gel-to-solution phase transition upon remote magnetic excitation. Thus, magnetic dehydrodipeptide-based hydrogels may find interesting applications as responsive Magnetic Resonance Imaging (MRI) contrast agents and for magnetic hyperthermia-triggered drug-release applications. Supramolecular hydrogels where the hydrogelator molecule is endowed with intrinsic pharmacological properties can potentially fulfill a dual function in drug delivery systems as (passive) nanocariers for incorporated drugs and as active drugs themselves. In this present study, we investigated the pharmacological activities of a panel of naproxen-dehydrodipeptide conjugates, previously studied for their hydrogelation ability and as nanocarriers for drug-delivery applications. A focused library of dehydrodipeptides, containing N-terminal canonical amino acids (Phe, Tyr, Trp, Ala, Asp, Lys, Met) N-capped with naproxen and linked to a C-terminal dehydroaminoacid (ΔPhe, ΔAbu), were evaluated for their anti-inflammatory and anti-cancer activities, as well as for their cytotoxicity to non-cancer cells, using a variety of enzymatic and cellular assays. All compounds except one were able to significantly inhibit lipoxygenase (LOX) enzyme at a similar level to naproxen. One of the compounds 4 was able to inhibit the cyclooxygenase-2 (COX-2) to a greater extent than naproxen, without inhibiting cyclooxygenase-1 (COX-1), and therefore is a potential lead in the search for selective COX-2 inhibitors. This hydrogelator is a potential candidate for dual COX/LOX inhibition as an optimised strategy for treating inflammatory conditions.

Assembly of amino acid containing naphthalene diimide-based molecules: the role of intervening amide groups in self-assembly, gelation, optical and semiconducting properties

Two naphthalene diimide containing molecules, one with a covalently linked peptide (P1) and the other with a covalently attached amino acid residue and a diamine moiety (P2), have been chosen in such a way that the number of intervening amide groups and the centrally located imide moieties are the same, and their molecular formulae are also identical. However, the positions of the amide groups are different in these two molecules and this can dictate a different behaviour in molecular assembly and gelation processes for each of the individual NDI-appended peptide (P1) and pseudo-peptide (P2). The molecule P1 with an attached peptide moiety and the intervening -CO-NH groups forms an organogel in a mixture of chloroform-methylcyclohexane at a very rapid rate and the mechanical strength of the gel is quite high, whereas the molecule P2, containing the amino acid and diamide moieties, and with the intervening -NH-CO groups forms an organogel in a relatively much slower rate in chloroform-methylcyclohexane mixture. The mechanical strength of the P2 gel is significantly lower compared to that of the P1 gel at the same concentration and solvent system. The minimum gelation concentration of P1 is much smaller than that of P2 in the same solvent system. The thermal stability of the P1 gel is higher than that of the P2 gel at the same concentration and solvent system. However, both of these gels form J-type aggregates in a mixture of chloroform-methylcyclohexane with a red shift in the UV-vis spectrum. The gelator P1 exhibits enhanced fluorescence compared to that of P2 at a fixed concentration and in the same solvent system (mixture of chloroform-methylcyclohexane, 5 : 95 (v/v)). The lifetime and quantum yield of the P1 gel are also significantly higher than those of the P2 gel under similar gelation conditions. Moreover, both P1 and P2 are found to exhibit significant semiconducting behaviours in their dried/xerogel states. It is important to note that the stronger gel P1 exhibits relatively better semiconducting behaviour than the weak gel P2. Interestingly, the self-assembly, gelation, photoluminescence and electrical conductivity are different for the gels obtained from these two molecules. This indicates the role of the amide bond and its linkage (whether -CONH/-NHCO) in the self-assembly, gelation and optoelectronic behaviour of these molecules in their assembled states.

Supramolecular Tripeptide Hydrogel Assembly with 5-Fluorouracil

In this work, we present Thioflavin T fluorescence, transmission electron microscopy (TEM), circular dichroism (CD), Fourier-transformed infrared (FT-IR), and oscillatory rheometry studies applied to an antineoplastic drug, 5-fluorouracil (5-FU), embedded in a heterochiral tripeptide hydrogel to obtain a drug delivery supramolecular system. The release of 5-fluorouracil was monitored over time by reverse-phase high-performance liquid chromatography (HPLC) and its interaction with the tripeptide assemblies was probed by all-atom molecular dynamics simulations.

Release of small bioactive molecules from physical gels

Pharmaceutical drugs with low water solubility have always received great attention within the scientific community. The reduced bioavailability and the need of frequent administrations have motivated the investigation of new drug delivery systems. Within this context, drug carriers that release their payload in a sustained way and hence reduce the administration rate are highly demanded. One interesting strategy to meet these requirements is the entrapment of the drugs into gels. So far, the most investigated materials for such drug-loaded gels are derived from polymers and based on covalent linkages. However, over the last decade the use of physical (or supramolecular) gels derived from low molecular weight compounds has experienced strong growth in this field, mainly due to important properties such as injectability, stimuli responsiveness and ease of synthesis. This review summarizes the use of supramolecular gels for the encapsulation and controlled release of small therapeutic molecules.

A Review on Recent Advances in Stabilizing Peptides/Proteins upon Fabrication in Hydrogels from Biodegradable Polymers

Hydrogels evolved as an outstanding carrier material for local and controlled drug delivery that tend to overcome the shortcomings of old conventional dosage forms for small drugs (NSAIDS) and large peptides and proteins. The aqueous swellable and crosslinked polymeric network structure of hydrogels is composed of various natural, synthetic and semisynthetic biodegradable polymers. Hydrogels have remarkable properties of functionality, reversibility, sterilizability, and biocompatibility. All these dynamic properties of hydrogels have increased the interest in their use as a carrier for peptides and proteins to be released slowly in a sustained manner. Peptide and proteins are remarkable therapeutic agents in today's world that allow the treatment of severe, chronic and life-threatening diseases, such as diabetes, rheumatoid arthritis, hepatitis. Despite few limitations, hydrogels provide fine tuning of proteins and peptides delivery with enormous impact in clinical medicine. Novels drug delivery systems composed of smart peptides and molecules have the ability to drive self-assembly and form hydrogels at physiological pH. These hydrogels are significantly important for biological and medical fields. The primary objective of this article is to review current issues concerned with the therapeutic peptides and proteins and impact of remarkable properties of hydrogels on these therapeutic agents. Different routes for pharmaceutical peptides and proteins and superiority over other drugs candidates are presented. Recent advances based on various approaches like self-assembly of peptides and small molecules to form novel hydrogels are also discussed. The article will also review the literature concerning the classification of hydrogels on a different basis, polymers used, "release mechanisms" their physical and chemical characteristics and diverse applications.