Molecular insights into the behaviour of bile salts at interfaces: a key to their role in lipid digestion

Hypotheses. Understanding the mechanisms underlying lipolysis is crucial to address the ongoing obesity crisis and associated cardiometabolic disorders. Bile salts (BS), biosurfactants present in the small intestine, play key roles in lipid digestion and absorption. It is hypothesised that their contrasting functionalities – adsorption at oil/water interfaces and shuttling of lipolysis products away from these interfaces – are linked to their structural diversity. We investigate the interfacial films formed by two BS, sodium taurocholate (NaTC) and sodium taurodeoxycholate (NaTDC), differing by the presence or absence of a hydroxyl group on their steroid skeleton. Experiments. Their adsorption behaviour at the air/water interface and interaction with a phospholipid monolayer – used to mimic a fat droplet interface – were assessed by surface pressure measurements and ellipsometry, while interfacial morphologies were characterised in the lateral and perpendicular directions by Brewster angle microscopy, X-ray and neutron reflectometry, and molecular dynamics simulations. Findings. Our results provide a comprehensive molecular-level understanding of the mechanisms governing BS interfacial behaviour. NaTC shows a higher affinity for the air/water and lipid/water interfaces, and may therefore favour enzyme adsorption, whereas NaTDC exhibits a higher propensity for desorption from these interfaces, and may thus more effectively displace hydrolysis products from the interface, through dynamic exchange

Interactions of bile salts with a dietary fibre, methylcellulose, and impact on lipolysis

Methylcellulose (MC) has a demonstrated capacity to reduce fat absorption, hypothetically through bile salt (BS) activity inhibition. We investigated MC cholesterol-lowering mechanism, and compared the influence of two BS, sodium taurocholate (NaTC) and sodium taurodeoxycholate (NaTDC), which differ slightly by their architecture and exhibit contrasting functions during lipolysis. BS/MC bulk interactions were investigated by rheology, and BS behaviour at the MC/water interface studied with surface pressure and ellipsometry measurements. In vitro lipolysis studies were performed to evaluate the effect of BS on MC-stabilised emulsion droplets microstructure, with confocal microscopy, and free fatty acids release, with the pH-stat method. Our results demonstrate that BS structure dictates their interactions with MC, which, in turn, impact lipolysis. Compared to NaTC, NaTDC alters MC viscoelasticity more significantly, which may correlate with its weaker ability to promote lipolysis, and desorbs from the interface at lower concentrations, which may explain its higher propensity to destabilise emulsions

Etude de la réactivité et de la nature des espèces actives dans l'oxydation en milieu aqueux du phénol par le peroxyde d'hydrogène, en présence de catalyseurs à base de fer déposé sur support carboné

POITIERS-BU Sciences (861942102) / SudocSudocFranceF

The oil-drop tensiometer: Potential applications for studying the kinetics of (phospho)lipase action

In 1987, Nury et al. adapted the well-known oil-drop technique for measuring interfacial tension for the purpose of monitoring the lipase hydrolysis of natural long-chain triacylglycerols. On the basis of this initial study, we developed an automated, digitised, computer-driven device with which we further prospected for applications of the oil-drop tensiometer in studies on lipolytic enzyme kinetics. In the present study, we first established that the new device provided reliable interfacial tension measurements, similar to those previously published. Furthermore, by keeping the oil-water interfacial tension at a fixed end-point value, the enzyme kinetics can be monitored using the change with time in the area of the oil drop. We then describe specific applications involving: (i) the measurement of lipase kinetics using minute amounts of enzyme; we checked the existence of a linear relationship between the initial decrease in the interfacial tension and the lipase concentration and found that the initial rates did not vary significantly between several successive drops formed within a 20-min period in the same lipase solution; (ii) the kinetic assay of phospholipase A 2 and (iii) studying the effects of high-pressure conditions upon lipase activity.link_to_subscribed_fulltex

The adsorption of biological peptides and proteins at the oil/water interface. A potentially important but largely unexplored field

This review focuses on some new techniques to study the behavior of peptides and proteins bound to oil droplets. We will show how model peptides e.g., amphipathic α helices (AαH) and amphipathic β strand (AβS) and some apolipoproteins adsorb to triacylglycerol (TAG) droplets and how they behave once adsorbed to the interface. While most of the studies described involve peptides and proteins at an oil/water interface, studies can also be carried out when the surface has been partially covered with phospholipids. This work is important because it examines biophysical changes that take place at lipid droplet interfaces and how this may relate to the metabolism of lipoproteins and lipid droplets