Reduction of enzymatic degradation of insulin via encapsulation in a lipidic bicontinuous cubic phase

Cubosome lipid nanocarriers for delivery of ultra-short antimicrobial peptides

HYPOTHESIS

Although antimicrobial peptides (AMPs) are a promising class of new antibiotics, their inherent susceptibility to degradation requires nanocarrier-mediated delivery. While cubosome nanocarriers have been extensively studied for delivery of AMPs, we do not currently understand why cubosome encapsulation improves antimicrobial efficacy for some compounds but not others. This study therefore aims to investigate the link between the mechanism of action and permeation efficiency of the peptides, their encapsulation efficacy, and the antimicrobial activity of these systems.

EXPERIMENTS

Encapsulation and delivery of Indolicidin, and its ultra-short derivative, Priscilicidin, were investigated using SAXS, cryo-TEM and circular dichroism. Molecular dynamics simulations were used to understand the loading of these peptides within cubosomes. The antimicrobial efficacy was assessed against gram-negative (E. coli) and gram-positive (MRSA) bacteria.

FINDINGS

A high ionic strength solution was required to facilitate high loading of the cationic AMPs, with bilayer encapsulation driven by tryptophan and Fmoc moieties. Cubosome encapsulation did not improve the antimicrobial efficacy of the AMPs consistent with their high permeation, as explained by a recent 'diffusion to capture model'. This suggests that cubosome encapsulation may not be an effective strategy for all antimicrobial compounds, paving the way for improved selection of nanocarriers for AMPs, and other antimicrobial compounds.

Permanently Charged Cationic Lipids-Evolution from Excipients to Therapeutic Lipids

Cationic lipids are crucial in medical and biotechnological applications including cellular transfection and gene delivery. Ionizable cationic lipids are critical components of the mRNA-based COVID vaccines while permanently charged cationic lipids have shown promise in cancer treatment. Despite significant research progress over the past few decades in designing improved, biocompatible cationic lipids, their transfection efficiency remains lower than that of viral vectors. Cationic lipids with additional functionalities like fusogenicity, stimuli-responsiveness, targeting capabilities, and therapeutic activity have been engineered to improve their performance. This review highlights the importance of molecular hybridization toward the design of biocompatible cationic lipids having fusogenic, stimuli-responsive, targeting, or therapeutic properties. This review mainly focuses on cationic lipids, having a permanent positive charge in the headgroup region, as these are typically employed to both increase cellular interactions and for improved loading, particularly for anionic nucleic acid-based therapeutics and vaccines. Structure-activity relationships between the lipid chemical structure (headgroup, spacer, hydrocarbon chain) and, to a lesser extent, the self-assembled nanostructure and the intrinsic biological activity of the multi-functional cationic lipids are described. Finally, the challenges involved in developing smart lipids without affecting their inherent capacity to self-assemble into structured nano-carriers are discussed.

Ephedra intermedia Schrenk & C. A. Mey Methanol Extract: Nanoencapsulation by Mini-Emulsion Polymerization and its Release Trend under Simulated Conditions of the Human Body

In this research, the extract of Ephedra intermedia Schrenk & C.A.Mey. was encapsulated using the mini-emulsion polymerization method based on methyl methacrylate polymers with a nanometer size. The encapsulated extract was characterized using different analytical techniques. Furthermore, the loading efficiency and release of the plant extract were examined. FT-IR spectroscopy confirmed the formation of an expectational product. The TEM and SEM imaging showed a spherical morphology for the prepared encapsulated extract. The average size of poly-methyl-methacrylate nanoparticles containing Ephedra extract was found to be approximately 47 nm. The extract loading efficiency and encapsulation efficiency test demonstrated a dose-depending behavior on E. intermedia extract for both analyses, which is highly advantageous for traversing biological barriers. The release assay shows a controlled release for the extract at phosphate buffer solution (PBS). A 38 % release was calculated after 36 hours. The results obtained from the present study reveal that encapsulating the plant extract is a suitable alternative to control and increase their medicinal properties.

A promising new oral delivery mode for insulin using lipid-filled enteric-coated capsules

The treatment of diabetes requires daily administration of the peptide insulin via subcutaneous (SC) injection due to poor stability following oral administration. Enteric capsules, designed to protect against low pH conditions in the stomach by providing a polymeric coating which only breaks down in the small intestine, have failed to significantly increase oral bioavailability for insulin. In parallel, amphiphilic lipid mesophases are versatile carrier materials which can protect encapsulated proteins and peptides from undesirable enzymatic degradation. Here we show the combined delivery capacity of a hydrated bicontinuous cubic lipid mesophase embedded within an enteric capsule. Animal studies demonstrated that the lipid filled enteric capsules could deliver insulin with bioavailabilities (relative to SC injection) as high as 99 % and 150 % for fast and slow acting insulin, respectively. These results provide a promising starting point towards further trials to develop an alternative, non-invasive mode for the delivery of insulin.

A lipidic mesophase with tunable release properties for the local delivery of macromolecules: the apoferritin nanocage, a case study

Lipid mesophases are able to incorporate and release a plethora of molecules, spanning from hydrophobic drugs to small hydrophilic proteins and therefore they have been widely used as drug delivery systems. However, their 3-5 nm water channels do not allow the release of large hydrophilic molecules such as monoclonal antibodies and therapeutic proteins. To overcome this major geometrical constraint, we designed a gel by mixing monoacylglycerol lipids, generally recognized as safe for human and/or animal use by FDA, and phospholipids, to obtain a material with swollen water channels suitable to host and further release macromolecules. Apoferritin, a 12 nm nanocage protein with intrinsic tumor-targeting properties able to incorporate several molecules, was selected here as the hydrophilic model protein to be embedded in the biocompatible gel. When immersed completely in the release media, mesophases with a swollen water channel of 22 nm, composed of monoolein and doped with 5 mole% of DOPS and 10 mole% of Chol allowed us to achieve a protein release of 60%, which is 120 times higher with respect to that obtained by employing non swollen-LMPs composed only of monoolein. Thus, the formulation can be administered locally to the rectal or vaginal mucosa, reducing the drawbacks often associated with the parenteral administration of bio-therapeutics. This approach would pave the way for the local application of other biomacromolecules (including human ferritin, monoclonal antibodies and antibody drug-conjugates) in those diseases easily reachable by a local application such as rectal or vaginal cancer.

Glucose sensitive konjac glucomannan/concanavalin A nanoparticles as oral insulin delivery system

Compared with injection, oral drug delivery is a better mode of administration because of its security, low pain and simplicity. Insulin is the first choice for clinical treatment of type 1 diabetes, but, because insulin inability to resist gastrointestinal (GI) digestion results in poor oral bioavailability of insulin. Herein, we developed a targeted oral delivery system for diabetes. ConA-INS-KGM nanoparticles were prepared, loaded with insulin, fabricated from konjac glucomannan (KGM) and concanavalin A (ConA) through a crosslinking method, as an insulin oral delivery system in response to different blood glucose levels. The size of nanoparticles was characterized by TEM, which showed that these nanoparticles were formed spherical particles with a diameter of about 500 nm. In vitro release of insulin from these nanoparticles was studied, which indicated that insulin release is reversible at different glucose concentrations. In vivo tests demonstrated that they are safe and have high biocompatibility. Using the nanoparticles to treat diabetic mice, we found that they can control blood sugar levels for 6 h, retaining their glucose-sensitive properties during this time. Therefore, these nanoparticles have significant potential as glucose-responsive systems for diabetes and show great applications in biomedical fields.

Uptake Dynamics of Cubosome Nanocarriers at Bacterial Surfaces and the Routes for Cargo Internalization

Antibiotic-resistant bacteria pose a significant threat to humanity. Gram-negative strains have demonstrated resistance to last resort antibiotics, partially due to their outer membrane, which hinders transport of antimicrobials into the bacterium. Nanocarrier (NC)-mediated drug delivery is one proposed strategy for combating this emerging issue. Here, the uptake of self-assembled lipid nanocarriers of cubic symmetry (cubosomes) into bacteria revealed fundamental differences in the uptake mechanism between Gram-positive and Gram-negative bacteria. For Gram-positive bacteria, the NCs adhere to the outer peptidoglycan layers and slowly internalize to the bacterium. For Gram-negative bacteria, the NCs interact in two stages, fusion with the outer lipid membrane and then diffusion through the inner wall. The self-assembled nature of the cubosomes imparts a unique ability to transfer payloads via membrane fusion. Remarkably, the fusion uptake mechanism allowed rapid NC internalization by the Gram-negative bacteria, overcoming the outer membrane responsible for their heightened resilience. Here this is demonstrated by the marked reduction in the minimal inhibition concentration required for antibiotics against a pathogenic strain of Gram-negative bacteria, Escherichia coli. These results provide mechanistic insight for the development of lipid NCs as a new tool to combat bacteria.

Cubic and Hexagonal Mesophases for Protein Encapsulation: Structural Effects of Insulin Confinement

Monoolein-based cubic and hexagonal mesophases were investigated as matrices for insulin loading, at low pH, as a function of temperature and in the presence of increasing amounts of oleic acid, as a structural stabilizer for the hexagonal phase. Synchrotron small angle X-ray diffraction, rheological measurements, and attenuated total reflection-Fourier transform infrared spectroscopy were used to study the effects of insulin loading on the lipid mesophases and of the effect of protein confinement in the 2D- and 3D-lipid matrix water channels on its stability and unfolding behavior. We found that insulin encapsulation has only little effects both on the mesophase structures and on the viscoelastic properties of lipid systems, whereas protein confinement affects the response of the secondary structure of insulin to thermal changes in a different manner according to the specific mesophase: in the cubic structure, the unfolding toward an unordered structure is favored, while the prevalence of parallel β-sheets, and nuclei for fibril formation, is observed in hexagonal structures.