Explicit-pH Coarse-Grained Molecular Dynamics Simulations Enable Insights into Restructuring of Intestinal Colloidal Aggregates with Permeation Enhancers

Medium-chain fatty acids and monoglycerides: Nanoarchitectonics-based insights into molecular self-assembly, membrane interactions, and applications

Medium-chain fatty acids (FAs) and monoglycerides (MGs) with saturated 6- to 12‑carbon long tails are single-chain lipid amphiphiles that demonstrate significant application merits. Key examples include their antimicrobial activity against antibiotic-resistant bacteria and emerging viral threats as well as innovations in oral pharmaceutics and biorenewable chemical production. These diverse functionalities are enabled by FA and MG self-assembly and their interactions with biological membranes. However, an integrated viewpoint connecting interfacial science principles to the broader application scope remains lacking. The objective of this review is to cover the latest progress in medium-chain FA and MG research and to build connections between molecular self-assembly, membrane interactions, and applications. By taking a bottom-up nanoarchitectonics perspective, we first examine molecular self-assembly principles, including ionization properties and formation of colloidal nanostructures such as micelles and vesicles. We then discuss membrane interaction concepts and experimental findings that illustrate how medium-chain FAs and MGs distinctly interact with phospholipid membranes. Based on this foundation, we highlight cutting-edge applications in medicine, agriculture, drug delivery, and sustainability, linking these advances to interfacial science concepts. In addition, we emphasize the growing convergence of experimental, theoretical, and computational approaches and offer a forward-looking perspective on future research needs and application opportunities.

Molecular Investigation of SNAC as an Oral Peptide Permeation Enhancer in Lipid Membranes via Solid-State NMR

Oral peptide therapeutics are increasingly favored in the pharmaceutical industry for their ease of use and better patient adherence. However, they face challenges with poor oral bioavailability due to their high molecular weight and surface polarity. Permeation enhancers (PEs) like salcaprozate sodium (SNAC) have shown promise in clinical trials, achieving about 1% bioavailability. One proposed mechanism for enhancing permeation is membrane perturbation or fluidization, though direct experimental proof and quantitative analysis of these effects are still needed. This study employs solid-state NMR (ssNMR) to investigate how SNAC interacts with hydrated DMPC liposomes, measuring enhancements in membrane fluidity across interfacial and transmembrane regions. The methodology involves analyzing phosphate lipid headgroups and acyl chains using static 31P chemical shift anisotropy and 2H quadrupolar coupling measurements alongside 1H and 13C magic angle spinning NMR for motional averaging of 1H-1H and 1H-13C dipolar couplings. Our findings indicate an overall increase in the uniaxial motion of phospholipids with SNAC in a PE concentration-dependent manner. It boosts lipid headgroup dynamics and enhancement plateaus at 25% between 24 and 72 mM concentrations. SNAC effectively enhances the fluidity of the hydrophobic center by 43% at 72 mM PE concentration, more significantly than the interfacial region. It is worth noting that the extent of liposome dissolution and conversion to micelles increases as SNAC concentration rises. Including a model peptide drug, octreotide, introduces a competitive equilibrium in this complex PE-lipid-peptide system, further influencing membrane dynamics for peptide permeation. Interestingly, the membrane enhancement does not show the expected plateau, and a less significant lipid mobility increase is observed in the presence of octreotide, suggesting a less substantial impact compared to peptide-free systems, which is likely due to peptide-PE interactions that consume monomeric SNAC, reducing its interaction with the lipid membrane. This study provides the first quantitative and site-specific ssNMR measurements of membrane mobility influenced by one representative PE as a snapshot of PE lipid interaction in a liposome model, demonstrating how peptide drugs modulate competitive equilibria and PE-induced lipid dynamics.

Coarse-Grained Molecular Dynamics Simulation of Heterogeneous Polysorbate 80 Surfactants and their Interactions with Small Molecules and Proteins

Polysorbate 80 (PS80) is widely used in pharmaceutical formulations, and its commercial grades exhibit certain levels of structural heterogeneity. The objective of this study was to apply coarse-grained molecular dynamics simulations to better understand the effect of PS80 heterogeneity on micelle self-assembly, the loading of hydrophobic small molecules into the micelle core, and the interactions between PS80 and a protein, bovine serum albumin (BSA). Four representative PS80 variants with different head and tail structures were studied. Our simulations found that PS80 structural heterogeneity could affect blank micelle properties such as solvent-accessible surface area, aggregation number, and micelle aspect ratio. It was also found that hydrophobic small molecules such as ethinyl estradiol preferentially partitioned into the PS80 micelle core and PS80 dioleates formed a more hydrophobic core compared to PS80 monooleates. Furthermore, multiple PS80 molecules could bind to BSA, and PS80 heterogeneity profoundly changed the binding ratio as well as the surfactant-protein contact area.

A. E. Albadri A, Patel H, Messaoudi S, Kadri A, M. Al-Hazmy S, Aouadi K. Synthesis, optical properties, DNA, β-cyclodextrin interaction, hydrogen isotope sensor and computational study of new enantiopure isoxazolidine derivative (ISoXD)

A novel isoxazolidine derivative (ISoXD) dye was successfully synthesized and comprehensively characterized. In this study, we conducted a thorough examination of its various properties, including optical characteristics, interactions with DNA and β-cyclodextrin (β-CD), molecular docking, molecular dynamic simulation, and density functional theory (DFT) calculations. Our investigation encompassed a systematic analysis of the absorption and emission spectra of ISoXD in diverse solvents. The observed variations in the spectroscopic data were attributed to the specific solvent's capacity to engage in hydrogen bonding interactions. Remarkably, the most pronounced intensities were observed in glycol, which can establish many hydrogen bonds with ISoXD. Furthermore, our study revealed a significant distinction in the fluorescence behavior of ISoXD when subjected to different solvents, particularly between CHCl3 and CDCl3. Moreover, we explored the fluorescence intensity of the ISoXD complex in the presence of various metals, both in ethanol and water. The ISoXD complex exhibited a substantial increase of fluorescence upon interaction with different metal ions. The utilization of DFT calculations allowed us to propose an intramolecular charge transfer (ICT) mechanism as a plausible explanation for this quenching phenomenon. The interaction of ISoXD with DNA and β-CD was studied using absorption spectra. The binding constant (K) and the standard Gibbs free energy change (ΔGo) for the interaction between DNA and β-CD with ISoXD were determined. In docking study, ISoXD exhibited significant docking scores (-6.511) and MM-GBSA binding free energies (-66.27 kcal/mol) within the PARP-1 binding cavity. Its binding pattern closely resembles to the co-crystal ligand veliparib, and during a 100ns MD simulation, ISoXD displayed strong stability and formed robust hydrogen bonds with key amino acids. These findings suggest ISoXD's potential as a PARP-1 inhibitor for further investigation in therapeutic development.

Revealing the interaction between peptide drugs and permeation enhancers in the presence of intestinal bile salts

Permeability enhancer-based formulations offer a promising approach to enhance the oral bioavailability of peptides. We used all-atom molecular dynamics simulations to investigate the interaction between two permeability enhancers (sodium caprate, and SNAC), and four different peptides (octreotide, hexarelin, degarelix, and insulin), in the presence of taurocholate, an intestinal bile salt. The permeability enhancers exhibited distinct effects on peptide release based on their properties, promoting hydrophobic peptide release while inhibiting water-soluble peptide release. Lowering peptide concentrations in the simulations reduced peptide-peptide interactions but increased their interactions with the enhancers and taurocholates. Introducing peptides randomly with enhancer and taurocholate molecules yielded dynamic molecular aggregation, and reduced peptide-peptide interactions and hydrogen bond formation compared to peptide-only systems. The simulations provided insights into molecular-level interactions, highlighting the specific contacts between peptide residues responsible for aggregation, and the interactions between peptide residues and permeability enhancers/taurocholates that are crucial within the mixed colloids. Therefore, our results can provide insights into how modifications of these critical contacts can be made to alter drug release profiles from peptide-only or mixed peptide-PE-taurocholate aggregates. To further probe the molecular nature of permeability enhancers and peptide interactions, we also analyzed insulin secondary structures using Fourier transform infrared spectroscopy. The presence of SNAC led to an increase in β-sheet formation in insulin. In contrast, both in the absence and presence of caprate, α-helices, and random structures dominated. These molecular-level insights can guide the design of improved permeability enhancer-based dosage forms, allowing for precise control of peptide release profiles near the intended absorption site.

Safety of surfactant excipients in oral drug formulations

Surfactants are a diverse group of compounds that share the capacity to adsorb at the boundary between distinct phases of matter. They are used as pharmaceutical excipients, food additives, emulsifiers in cosmetics, and as household/industrial detergents. This review outlines the interaction of surfactant-type excipients present in oral pharmaceutical dosage forms with the intestinal epithelium of the gastrointestinal (GI) tract. Many surfactants permitted for human consumption in oral products reduce intestinal epithelial cell viability in vitro and alter barrier integrity in epithelial cell monolayers, isolated GI tissue mucosae, and in animal models. This suggests a degree of mis-match for predicting safety issues in humans from such models. Recent controversial preclinical research also infers that some widely used emulsifiers used in oral products may be linked to ulcerative colitis, some metabolic disorders, and cancers. We review a wide range of surfactant excipients in oral dosage forms regarding their interactions with the GI tract. Safety data is reviewed across in vitro, ex vivo, pre-clinical animal, and human studies. The factors that may mitigate against some of the potentially abrasive effects of surfactants on GI epithelia observed in pre-clinical studies are summarised. We conclude with a perspective on the overall safety of surfactants in oral pharmaceutical dosage forms, which has relevance for delivery system development.

Numerical simulation of peristalsis to study co-localization and intestinal distribution of a macromolecular drug and permeation enhancer

In this work, simulations of intestinal peristalsis are performed to investigate the intraluminal transport of macromolecules (MMs) and permeation enhancers (PEs). Properties of insulin and sodium caprate (C₁₀) are used to represent the general class of MM and PE molecules. Nuclear magnetic resonance spectroscopy was used to obtain the diffusivity of C₁₀, and coarse-grain molecular dynamics simulations were carried out to estimate the concentration-dependent diffusivity of C₁₀. A segment of the small intestine with the length of 29.75 cm was modeled. Peristaltic speed, pocket size, release location, and occlusion ratio of the peristaltic wave were varied to study the effect on drug transport. It was observed that the maximum concentration at the epithelial surface for the PE and the MM increased by 397 % and 380 %, respectively, when the peristaltic wave speed was decreased from 1.5 to 0.5 cm s^-1. At this wave speed, physiologically relevant concentrations of PE were found at the epithelial surface. However, when the occlusion ratio is increased from 0.3 to 0.7, the concentration approaches zero. These results suggest that a slower-moving and more contracted peristaltic wave leads to higher efficiency in transporting mass to the epithelial wall during the peristalsis phases of the migrating motor complex.