NMR and ESR study of amphotericin B interactions with various binary phosphatidylcholine/phosphatidylglycerol membranes

Biological and thermodynamic stabilization of lipid-based delivery systems through natural biopolymers; controlled release and molecular dynamics simulations

Nowadays, the use of lipid-based nanocarriers for the targeted and controlled delivery of a variety of hydrophobic and hydrophilic bioactive-compounds and drugs has increased significantly. However, challenges such as thermodynamic instability, oxidation, and degradation of lipid membranes, as well as the unintended release of loaded compounds, have limited the use of these systems in the food and pharmaceutical industries. Therefore, the present study reviews the latest achievements in evaluating the characteristics, production methods, challenges, functional, and biological stabilization strategies of lipid-based carriers (including changes in formulation composition, structural modification, membrane-rigidity, and finally monolayer or multilayer coating with biopolymers) in different conditions, as well as molecular dynamics simulations. The scientists' findings indicate the effect of natural biopolymers (such as chitosan, calcium alginate, pectin, dextran, xanthan, caseins, gelatin, whey-proteins, zein, and etc.) in modifying the external structure of lipid-based carriers, improving thermodynamic stability and resistance of membranes to physicochemical and mechanical tensions. However, depending on the type of bioactive compound as well as the design and production goals of the delivery-system, selecting the appropriate biopolymer has a significant impact on the stability of vesicles and maintaining the bioaccessibility of the loaded-compounds due to the stresses caused by the storage-conditions, formulation, processing and gastrointestinal tract.

Advanced Methods for Studying Structure and Interactions of Macrolide Antibiotics

Macrolide antibiotics are macrocyclic compounds that are clinically used and prescribed for the treatment of upper and lower respiratory tract infections. They inhibit the synthesis of bacterial proteins by reversible binding to the 23S rRNA at or near the peptidyl transferase center. However, their excellent antibacterial profile was largely compromised by the emergence of bacterial resistance. Today, fighting resistance to antibiotics is one of the greatest challenges in medicinal chemistry. Considering various physicochemical properties of macrolides, understanding their structure and interactions with macromolecular targets is crucial for the design of new antibiotics efficient against resistant pathogens. The solid-state structures of some macrolide-ribosome complexes have recently been solved, throwing new light on the macrolide binding mechanisms. On the other hand, a combination of NMR spectroscopy and molecular modeling calculations can be applied to study free and bound conformations in solution. In this article, a description of advanced physicochemical methods for elucidating the structure and interactions of macrolide antibiotics in solid state and solution will be provided, and their principal advantages and drawbacks will be discussed.

Biophysical approaches for exploring lipopeptide-lipid interactions

In recent years, lipopeptides (LPs) have attracted a lot of attention in the pharmaceutical industry due to their broad-spectrum of antimicrobial activity against a variety of pathogens and their unique mode of action. This class of compounds has enormous potential for application as an alternative to conventional antibiotics and for pest control. Understanding how LPs work from a structural and biophysical standpoint through investigating their interaction with cell membranes is crucial for the rational design of these biomolecules. Various analytical techniques have been developed for studying intramolecular interactions with high resolution. However, these tools have been barely exploited in lipopeptide-lipid interactions studies. These biophysical approaches would give precise insight on these interactions. Here, we reviewed these state-of-the-art analytical techniques. Knowledge at this level is indispensable for understanding LPs activity and particularly their potential specificity, which is relevant information for safe application. Additionally, the principle of each analytical technique is presented and the information acquired is discussed. The key challenges, such as the selection of the membrane model are also been briefly reviewed.

Preparation, Characterization, and In Vivo Pharmacokinetic Study of the Supercritical Fluid-Processed Liposomal Amphotericin B

Here, we aimed to prepare and optimize liposomal amphotericin B (AmB) while using the supercritical fluid of carbon dioxide (SCF-CO₂) method and investigate the characteristics and pharmacokinetics of the SCF-CO₂-processed liposomal AmB. Liposomes containing phospholipids, ascorbic acid (vit C), and cholesterol were prepared by the SCF-CO₂ method at an optimized pressure and temperature; conventional liposomes were also prepared using the thin film hydration method and then compared with the SCF-CO₂-processed-liposomes. The optimized formulation was evaluated by in vitro hemolysis tests on rat erythrocytes and in vivo pharmacokinetics after intravenous administration to Sprague-Dawley rats and compared with a marketed AmB micellar formulation, Fungizone^®, and a liposomal formulation, AmBisome^®. The results of the characterization studies demonstrated that the SCF-CO₂-processed-liposomes were spherical particles with an average particle size of 137 nm (after homogenization) and drug encapsulation efficiency (EE) was about 90%. After freeze-drying, mean particle size, EE, and zeta potential were not significantly changed. The stability study of the liposomes showed that liposomal AmB that was prepared by the SCF method was stable over time. In vivo pharmacokinetics revealed that the SCF-CO₂-processed-liposomes were bioequivalent to AmBisome^®; the hemolytic test depicted less hematotoxicity than Fungizone^®. Therefore, this method could serve as a potential alternative for preparing liposomal AmB for industrial applications.