A Rat Model of Human Lipid Emulsion Digestion

Abstract

A better understanding of how dietary lipids are processed by the human body is necessary to allow for the control of satiation and energy intake by tailored lipid systems. To examine whether rats are a valid model of human dietary lipid processing and therefore useful for further mechanistic studies in this context, we tested in rats three lipid emulsions of different stability, which alter satiety responses in humans. Different sets of 15 adult male Sprague Dawley rats, equipped with gastric catheters alone or combined with hepatic portal vein (HPV) and vena cava (VC) catheters were maintained on a medium-fat diet and adapted to an 8 h deprivation/16 h feeding schedule. Experiments were performed in a randomized cross-over study design. After gastric infusion of the lipid emulsions, we assessed gastric emptying by the paracetamol absorption test and recorded in separate experiments food intake and plasma levels of gastrointestinal hormones and metabolites in the HPV. For an acid stable emulsion, slower gastric emptying and an enhanced release of satiating gastrointestinal (GI) hormones were observed and were associated with lower short-term energy intake in rats and less hunger in humans, respectively. The magnitude of hormonal responses was related to the acid stability and redispersibility of the emulsions and thus seems to depend on the availability of lipids for digestion. Plasma metabolite levels were unaffected by the emulsion induced changes in lipolysis. The results support that structured lipid systems are digested similarly in rats and humans. Thus unstable emulsions undergo the same intragastric destabilization in both species, i.e., increased droplet size and creaming. This work establishes the rat as a viable animal model for in vivo studies on the control of satiation and energy intake by tailored lipid systems.

Lipid emulsion interfacial design modulates human in vivo digestion and satiation hormone response

“…LEs were produced from 20 wt% canola oil (Sabo) and Evian water using different emulsifiers. PS-LE1 was prepared according to previous studies 12,24,25,[27][28][29] using 0.8 wt% small molecular weight surfactant polysorbate 80 (Palsgaard) and 0.8 wt% xanthan (KELTROL, CP Kelco) to increase viscosity. The novel LE5 -LE7 were prepared as described in detail by Scheuble et al 7 In brief, WPI-LE5 was stabilized by 1 wt% WPI (BiPro, Davisco), MC-LE6 was stabilized by 4 wt% MC A15 (Dow Chemicals), and CNC-LE7 was stabilized by 4 wt% CNCs (CelluForce).…”

“…The droplet diameter was ≈ 0.3 µm for PS-LE1, 0.4 µm for MC-LE6, and 1 µm for WPI-LE5 and CNC-LE7 as reported in our previous studies. 7,24 For LEs stabilized with the same emulsifier a smaller droplet size results in a higher specific surface area for lipolysis which can accelerate satiation hormone response. 16 However, for LEs stabilized with different emulsifiers, emulsifier-specific effects like gastric structuring, changes in droplet size during digestion, and interfacial competition with lipases are more pronounced.…”

“…LE1 is stable and evenly dispersed in the stomach, exhibits a steady gastric emptying, and relatively high levels of plasma FFA and satiation hormones compared to other LEs. 24,25,[27][28][29][30] LE5 is stabilized by whey protein isolate (WPI), a common emulsifier in food industry. As is typical for protein-stabilized LEs, LE5 is unstable under gastric conditions due to rapid displacement by lipases and proteolysis leading to lipid layering in the stomach.…”

“…23 However, LE digestion can differ considerably in vivo particularly when regarding gastric structuring 7 and LE-specific emptying rates. 24 Hence, in vivo validation of such LEs and their effect on satiation are crucial, but remain scarce to date. Clifton and colleagues [25][26][27] introduced a set of emulsions with altering emulsifier type to study their effects on in vivo gastric structuring, fat emptying, and satiation hormone response.…”

“…These LEs, which were serially numbered LE1-LE4, have since been readily employed for in vivo experiments. 12,24,[28][29][30] We have recently expanded this set by three novel LEs (termed LE5 -LE7 for consistency) stabilized with alternative emulsifiers which are able to alter gastric structuring and lipolysis in humans. 7 Here, we further assess the ability of LE5-LE7 to modulate in vivo digestion in terms of gastric emptying, plasma metabolite and hormone response, postprandial hunger and food consumption in humans compared to the established LE1.…”