How motility can enhance mass transfer and absorption in the duodenum: Taking the structure of the villi into account

Computational insights into colonic motility: Mechanical role of mucus in homeostasis and inflammation

Colonic motility plays a vital role in maintaining proper digestive function. The rhythmic contractions and relaxations facilitate various types of motor functions that generate both propulsive and non-propulsive motility modes which in turn generate shear stresses on the epithelial surface. However, the interplay between colonic mucus, shear stress, and epithelium remains poorly characterized. Here, we present a colonic computational model that describes the potential roles of mucus and shear stress in both homeostasis and ulcerative colitis (UC). Our model integrates several key features, including the properties of the mucus bilayer and faeces, intraluminal pressure, and crypt characteristics to predict the time-space mosaic of shear stress. We show that the mucus thickness which could vary based on the severity of UC, may significantly reduce the amount of shear stress applied to the colonic crypts and effect faecal velocity. Our model also reveals an important spatial shear stress variance in homeostatic colonic crypts that suggests shear stress may have a modulatory role in epithelial cell migration, differentiation, apoptosis, and immune surveillance. Together, our study uncovers the rather neglected roles of mucus and shear stress in intestinal cellular processes during homeostasis and inflammation.

In vitro release and bioaccessibility of oral solid preparations in a dynamic gastrointestinal system simulating fasted and fed states: A case study of metformin hydrochloride tablets

Food and formulation characteristics are crucial factors affecting the gastrointestinal release and absorption kinetics of oral solid preparations. In the present study, the dynamic continuous release and bioaccessibility of metformin hydrochloride immediate-release (IR) and sustained-release (SR) tablets were investigated in the dynamic human stomach-intestine (DHSI-IV) system simulating fasted and fed states in healthy adults. Both tablet formulations (particularly IR tablet) exhibited a postponed release in the fed state compared to the fasted state. Correspondingly, the bioaccessible fraction of metformin from IR tablets in the presence of high-fat meal was significantly reduced to 76.2 % of the fasted state. However, the in vitro bioaccessibility was less impaired by food for SR tablets with a fed/fasted ratio of 95.5 %. A convolution-based approach was used to convert in vitro bioaccessibility results to plasma concentration data. The predicted plasma concentration curve showed good agreement with human data in terms of pharmacokinetic (PK) parameters. In the fasted state, the predicted Cmax, Tmax and AUC0-24h of IR tablets were 943.9 ± 25.7 ng/mL, 2.0 ± 0.4 h and 7090.7 ± 112.0 ng.h/mL, respectively, mirroring values observed in healthy subjects. Overall, the DHSI-IV system has demonstrated potential to assess and predict the impact of meal intake on the in vivo release and absorption behaviors of oral solid preparations.

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.

Intestinal absorption of DHA microcapsules with different formulations based on ex vivo rat intestine and in vitro dialysis models

Intestinal permeability is a key factor affecting the bioavailability and physiological efficacy of docosahexaenoic acid (DHA) encapsulated in microcapsules. However, how the DHA microcapsules are transformed and the components absorbed across the small intestinal membrane has seldom been examined previously. In this study, an ex vivo absorption model based on the permeability of the rat small intestine was established to evaluate the intestinal absorption of DHA microcapsules with five formulations after gastrointestinal digestion in vitro. For pure glucose solutions, the apparent permeability coefficient (P_app) increased from 5.70 ± 0.60 × 10^-6 cm s^-1 at 5 mg mL^-1 to 20.25 ± 0.88 × 10^-6 cm s^-1 at 30 mg mL^-1 and decreased to 15.73 ± 0.91 × 10^-6 cm s^-1 at 100 mg mL^-1. The P_app values obtained using the ex vivo model are comparable to those reported in the human jejunum. For algal oil DHA microcapsules with whey protein as the wall material (A-WP-DHA) after in vitro digestion, the P_app of glucose released was 3.81 × 10^-6 cm s^-1 with an absorption ratio of 59.55% in the ex vivo model, significantly lower than that from the in vitro porcine casing model. The P_app and absorption ratio varied little among the in vitro dialysis models with different molecular weight cut-off values. A similar trend was observed for the absorption of amino acids. However, the absorption ratio (26.6%) was the highest in the ex vivo model for free fatty acids (FFAs) released from the microcapsules due to the rapid accumulation of compounds on the inner wall of the intestinal sac. In addition, the DHA microcapsules with algal oil as the DHA source (36.40%) exhibited a higher absorption ratio of FFAs than that from tuna oil (14.26%) in the ex vivo model. The wall material compositions seemed to have little effect on FFA absorption. The present study is practically meaningful for the future formulation of DHA microcapsules with enhanced absorption.

A review on curcumin colon-targeted oral drug delivery systems for the treatment of inflammatory bowel disease

Synthetic drugs and monoclonal antibodies are the typical treatments to combat inflammatory bowel disease (IBD). However, side effects are present when these treatments are used, and their continued application could be restricted by the high relapse rate of the disease. One potential alternative to these treatments is the use of plant-derived products. The use curcumin is one such treatment option that has seen an increase in usage in treating IBD. Curcumin is derived from a rhizome of turmeric (Curcuma longa), and the results of studies on the use of curcumin to treat IBD are promising. These studies suggest that curcumin interacts with cellular targets such as NF-κB, JAKs/STATs, MAPKs, TNF-α, IL-6, PPAR, and TRPV1 and may reduce the progression of IBD. Potentially, curcumin can be used as a therapeutic agent for patients with IBD when it reduces the incidence of clinical relapse. This review discusses the strategies utilized in designing and developing an oral colonic delivery dosage form of curcumin.

The final fate of food: On the establishment of in vitro colon models

The search for life/health quality has driven the search for a better understanding of food components on the overall individual health, which turns to be intrinsically related to the digestive system. In vitro digestion models are considered an alternative for the in vivo studies for a variety of practical reasons, but further research is still needed concerning the colon model establishment. An effective in vitro colon model should consider all unit operations and transport phenomena, together with chemical and biochemical reactions, material handling and reactor design. Due to the different techniques and dependence on the donor microbiota, it is difficult to obtain a standard protocol with results reproductible in time and space. Furthermore, the colon model should be fed with a representative substrate, thus what happens in upper digestion tract and absorption prior to colon is also of crucial importance. Essentially, there are two ways to think about how to achieve a good and useful in vitro colon model: a complex biomimetic system that provides results comparable with the in vivo studies or a simple system, that despite the fact it could not give physiologically relevant data, it is sufficient to understand the fate of some specific components.

In-vitro digestion models: a critical review for human and fish and a protocol for in-vitro digestion in fish

Digestive systems in human, animals, and fish are biological reactors and membranes to digest food and extract nutrients. Therefore, static and dynamic models of in-vitro digestion systems are developed to study e.g. novel food and feed before in-vivo studies. Such models are well developed for human, but not to the same extent for animals and fish. On the other hand, recent advances in aquaculture nutrition have created several potential fish meal replacements, and the assessment of their nutrient digestibility is critical in the application as a fish meal replacement. Using an in-vitro method, the assessment of an ingredient digestibility could be faster and less expensive compared to using an in-vivo experiment. An in-vitro method has been widely used to assess food nutrient digestibility for humans; however, its application for fish is still in the early stages. Both the human and fish as monogastric vertebrates share similar gastrointestinal systems; thus, the concept from the application for humans could be applied for fish. This review aims to improve the in-vitro digestion protocol for fish by adapting the concept from then study for humans, summarizing the current available in-vitro digestion model developed for human and fish in-vitro digestion study, identifying challenges specifically for fish required to be tackled and suggesting an engineering approach to adapt the human in-vitro gastrointestinal model to fish. Protocols to conduct in-vitro digestion study for fish are then proposed.

Determining the glycaemic responses of foods: conventional and emerging approaches

A low-glycaemic diet is crucial for those with diabetes and cardiovascular diseases. Information on the glycaemic index (GI) of different ingredients can help in designing novel food products for such target groups. This is because of the intricate dependency of material source, composition, food structure and processing conditions, among other factors, on the glycaemic responses. Different approaches have been used to predict the GI of foods, and certain discrepancies exist because of factors such as inter-individual variation among human subjects. Besides other aspects, it is important to understand the mechanism of food digestion because an approach to predict GI must essentially mimic the complex processes in the human gastrointestinal tract. The focus of this work is to review the advances in various approaches for predicting the glycaemic responses to foods. This has been carried out by detailing conventional approaches, their merits and limitations, and the need to focus on emerging approaches. Given that no single approach can be generalised to all applications, the review emphasises the scope of deriving insights for improvements in methodologies. Reviewing the conventional and emerging approaches for the determination of GI in foods, this detailed work is intended to serve as a state-of-the-art resource for nutritionists who work on developing low-GI foods.