Real-time measurements to characterize dynamics of emulsion interface during simulated intestinal digestion

FRET-Sensing of Multivalent Protein Binding at the Interface of Biomimetic Microparticles Functionalized with Fluorescent Glycolipids

Cell adhesion is a central process in cellular communication and regulation. Adhesion sites are triggered by specific ligand-receptor interactions inducing the clustering of both partners at the contact point. Investigating cell adhesion using microscopy techniques requires targeted fluorescent particles with a signal sensitive to the clustering of receptors and ligands at the interface. Herein, we report on simple cell or bacterial mimics, based on liquid microparticles made of lipiodol functionalized with custom-designed fluorescent lipids. These lipids are targeted toward lectins or biotin membrane receptors, and the resulting particles can be specifically identified and internalized by cells, as demonstrated by their phagocytosis in primary murine bone marrow-derived macrophages. We also evidence the possibility to sense the binding of a multivalent lectin, concanavalin A, in solution by monitoring the energy transfer between two matching fluorescent lipids on the surface of the particles. We anticipate that these liquid particle-based sensors, which are able to report via Förster resonance energy transfer (FRET) on the movement of ligands on their interface upon protein binding, will provide a useful tool to study receptor binding and cooperation during adhesion processes such as phagocytosis.

Nanoliposome-Mediated Encapsulation of Chlorella Oil for the Development of a Controlled-Release Lipid-Lowering Formulation

Chlorella oil nanoliposomes (CO-NLP) were synthesized through ultrasonic injection with ethanol, and their physicochemical properties and hypolipidemic efficacy were systematically investigated. The results revealed that the mean particle size of CO-NLP was 86.90 nm and the encapsulation efficiency (EE) was 92.84%. Storage conditions at 4 °C were conducive to the stability of CO-NLP, maintaining an EE of approximately 90% even after 10 days of storage. The release profile of CO-NLP adhered more closely to the first-order kinetic model during in vitro assessments, exhibiting a slower release rate compared to free microalgae oil. In simulated in vitro digestion experiments, lipolytic reactions of CO-NLP were observed during intestinal digestion subsequent to nanoliposome administration. Notably, the inhibitory effect of CO-NLP on cholesterol esterase activity was measured at 85.42%. Additionally, the average fluorescence intensity of nematodes in the CO-NLP group was 52.17% lower than in the control group at a CO-NLP concentration of 500 μg/mL, which suggests a pronounced lipid-lowering effect of CO-NLP. Therefore, the CO-NLP exhibited characteristics of small and uniform particle size, elevated storage stability, gradual release during intestinal digestion, and a noteworthy hypolipidemic effect. These findings designate CO-NLP as a novel lipid-lowering active product, demonstrating potential for the development of functional foods.

Bile salts in digestion and transport of lipids

Because of their unusual chemical structure, bile salts (BS) play a fundamental role in intestinal lipid digestion and transport. BS have a planar arrangement of hydrophobic and hydrophilic moieties, which enables the BS molecules to form peculiar self-assembled structures in aqueous solutions. This molecular arrangement also has an influence on specific interactions of BS with lipid molecules and other compounds of ingested food and digestive media. Those comprise the complex scenario in which lipolysis occurs. In this review, we discuss the BS synthesis, composition, bulk interactions and mode of action during lipid digestion and transport. We look specifically into surfactant-related functions of BS that affect lipolysis, such as interactions with dietary fibre and emulsifiers, the interfacial activity in facilitating lipase and colipase anchoring to the lipid substrate interface, and finally the role of BS in the intestinal transport of lipids. Unravelling the roles of BS in the processing of lipids in the gastrointestinal tract requires a detailed analysis of their interactions with different compounds. We provide an update on the most recent findings concerning two areas of BS involvement: lipolysis and intestinal transport. We first explore the interactions of BS with various dietary fibres and food emulsifiers in bulk and at interfaces, as these appear to be key aspects for understanding interactions with digestive media. Next, we explore the interactions of BS with components of the intestinal digestion environment, and the role of BS in displacing material from the oil-water interface and facilitating adsorption of lipase. We look into the process of desorption, solubilisation of lipolysis, products and formation of mixed micelles. Finally, the BS-driven interactions of colloidal particles with the small intestinal mucus layer are considered, providing new findings for the overall assessment of the role of BS in lipid digestion and intestinal transport. This review offers a unique compilation of well-established and most recent studies dealing with the interactions of BS with food emulsifiers, nanoparticles and dietary fibre, as well as with the luminal compounds of the gut, such as lipase-colipase, triglycerides and intestinal mucus. The combined analysis of these complex interactions may provide crucial information on the pattern and extent of lipid digestion. Such knowledge is important for controlling the uptake of dietary lipids or lipophilic pharmaceuticals in the gastrointestinal tract through the engineering of novel food structures or colloidal drug-delivery systems.

Real-time measurements of milk fat globule membrane modulation during simulated intestinal digestion using electron paramagnetic resonance spectroscopy

Milk Fat Globules with their unique interfacial structure and membrane composition are a key nutritional source for mammalian infants, however, there is a limited understanding of the dynamics of fat digestion in these structures. Lipid digestion is an interfacial process involving interactions of enzymes and bile salts with the interface of suspended lipid droplets in an aqueous environment. In this study, we have developed an electron paramagnetic resonance spectroscopy approach to evaluate real time dynamics of milk fat globules interfacial structure during simulated intestinal digestion. To measure these dynamics, natural milk fat globule membrane was labeled with EPR-active probe, partitioning of EPR probes into MFGs membrane was validated using saturation-recovery measurements and calculation of the depth parameter Φ. After validation, the selected spin probe was used to evaluate the membrane's fluidity as a measure of the interface's modulation in the presence of bile salts and pancreatic lipase. Independently, bile salts were found to have a rigidifying effect on the spin probed MFGM, while pancreatic lipase resulted in an increase in membrane fluidity. When combined, the effect of lipase appears to be diminished in the presence of bile salts. These results indicate the efficacy of EPR in providing an insight into small time scale molecular dynamics of phospholipid interfaces in milk fat globules. Understanding interfacial dynamics of naturally occurring complex structures can significantly aid in understanding the role of interfacial composition and structural complexity in delivery of nutrients during digestion.

Colloidal aspects of dispersion and digestion of self-dispersing lipid-based formulations for poorly water-soluble drugs

Self-dispersing lipid-based formulations, particularly self-microemulsifying drug delivery systems (SMEDDS) have gained an increased interest in recent times as a means to enhance the oral bioavailability of poorly water-soluble lipophilic drugs. Upon dilution, SMEDDS self-emulsify in an aqueous fluid and usually form a kinetically stable oil-in-water emulsion or in some rare cases a true thermodynamically stable microemulsion. The digestion of the formulation leads to the production of amphiphilic digestion products that interact with endogenous amphiphilic components and form self-assembled colloidal phases in the aqueous environment of the intestine. The formed colloidal phases play a pivotal role in maintaining the lipophilic drug in the solubilised state during gastrointestinal transit prior to absorption. Thus, this review describes the structural characterisation techniques employed for SMEDDS and the recent literature studies that elucidated the colloidal aspects during dispersion and digestion of SMEDDS and solid SMEDDS. Possible future studies are proposed to gain better understanding on the colloidal aspects of SMEDDS and solid SMEDDS.

In situ monitoring of the structural change of microemulsions in simulated gastrointestinal conditions by SAXS and FRET

Microemulsions are promising drug delivery systems for the oral administration of poorly water-soluble drugs. However, the evolution of microemulsions in the gastrointestinal tract is still poorly characterized, especially the structural change of microemulsions under the effect of lipase and mucus. To better understand the fate of microemulsions in the gastrointestinal tract, we applied small-angle X-ray scattering (SAXS) and fluorescence resonance energy transfer (FRET) to monitor the structural change of microemulsions under the effect of lipolysis and mucus. First, the effect of lipolysis on microemulsions was studied by SAXS, which found the generation of liquid crystalline phases. Meanwhile, FRET spectra indicated micelles with smaller particle sizes were generated during lipolysis, which could be affected by CaCl2, bile salts and lecithin. Then, the effect of mucus on the structural change of lipolysed microemulsions was studied. The results of SAXS and FRET indicated that the liquid crystalline phases disappeared, and more micelles were generated. In summary, we studied the structural change of microemulsions in simulated gastrointestinal conditions by SAXS and FRET, and successfully monitored the appearance and disappearance of the liquid crystalline phases and micelles.

Calcium Alters the Interfacial Organization of Hydrolyzed Lipids during Intestinal Digestion

Calcium plays an important dual role in lipid digestion: promoting removal of long-chain fatty acids from the oil-water interface by forming insoluble calcium soaps while also limiting their bioaccessibility. This becomes more significant in food containing high calcium concentration, such as dairy products. Nevertheless, scarce attention has been paid to the effect of calcium on the interfacial properties during lipid digestion, despite this being largely an interfacial reaction. This study focused on the dynamics of the formation of calcium soaps at the oil-water interface during lipolysis by pancreatic lipase in the absence and presence of the two primary human bile salts (sodium glycocholate or sodium glycochenodeoxycholate). The competitive adsorption of lipase, bile salts, and lipolysis products, as well as the formation of calcium soaps in the presence of increasing concentrations of calcium were mainly characterized by recording the interfacial tension and dilatational modulus in situ. In the absence of bile salts, calcium complexes with fatty acids at the oil-water interface forming a relatively strong viscoelastic network of calcium soaps over time. The dilatational modulus of the calcium soap network is directly related to the interfacial concentration of lipolysis products and the calcium bulk concentration. Calcium soaps are also visualized forming a continuous rough layer on the surface of oil droplets immersed in simulated intestinal aqueous phase. Despite bile salts having different surface activity, they play a similar role on the interfacial competition with lipase and lipolysis products although altering their kinetics. The presence of bile salts disrupts the network of calcium soaps, as suggested by the decrease in the dilatational modulus and the formation of calcium soap islands on the surface of the oil droplets. The accelerant effect of calcium on lipolysis is probably because of fatty acid complexation and subsequent removal from the interface rather than reduced electrostatic repulsion between lipase and bile salt molecules and promoted lipase adsorption. The work shown here has implications for the delivery of oil-soluble bioactives in the presence of calcium.