Invitro digestion models
Understanding the outcome of the ingested food components in the human digestive system is an area of interest for researchers because of its relation to nutrition and health. Foods contain components that can have either beneficial or adverse effects on human health. Consumed foods are combinations of diverse phases and structures depending on their sources, formulations, and processes used for their production. The digestive system must physically and chemically break down ingested food to release its components, which will be further metabolized to be used by the body.
Digestion of food in the human digestive system is a complex combination of versatile and multiple-scale physicochemical processes that steer the food intake, disintegration to suitable forms, absorption of the basic units, transportation to related organs, and purging the remaining waste.
Increased interest in modifying the matrix and structural characteristics of foods to optimize their digestion and absorption behavior for health benefit requires implementing many food digestion studies in the digestive tract.
However, studying human digestion’s intricate process is complicated, costly, varies from person to person, and constrained by ethical considerations.
Let’s know about Invitro?
What is Invitro?
In vitro (Latin for "in glass") refers to experiments or processes conducted outside of a living organism, typically in a laboratory setting. It is the opposite of in vivo, which refers to experiments or processes conducted within a living organism. In vitro studies are commonly used in various scientific disciplines, including biology, medicine, pharmacology, and biochemistry, to understand biological processes, test hypotheses, and evaluate the effects of substances or treatments.
Now let’s know.
what is Invitro digestion?
In vitro digestion refers to the process of simulating the digestion of food outside of the human body in a laboratory setting. It involves replicating the various stages of digestion, including oral, gastric, and intestinal phases, using specific enzymes and conditions to mimic the physiological processes that occur in the digestive system.
In vitro models are preferred in food, nutrition, and medical research because of their speed, cost, and reproducibility due to used standardized conditions compared to in vivo studies.
In food digestion, substrate-enzyme ratio, pH profiles, and transport of digested products are important parameters. Therefore, in vitro, static models that lack dynamic and mechanic actions have limitations for accurately predicting accessible nutrients or food behavior during digestion.
There are several models of invitro digestion models.
1. TNO gastrointestinal model (TIM)
The in vitro gastrointestinal model (TIM) was developed at TNO Nutrition and Food Research Center (Zeist, The Netherlands) in the early 1990s. TIM is a computer-controlled multi-compartmental dynamic system that simulates the gastrointestinal system. The system aimed to simulate the main physiological conditions that change with time and location, such as contractions, transit time, pH, composition, and secretion rate of digestive fluids, absorption of nutrients, and water in a reproducible and controllable manner. In the system, computer simulations used the protocols that were prepared with valid in vivo data. Specialized protocols depending on age and health status, as well as on the type of food, can be generated.
TIM is one of the successful in vitro dynamic systems and has been widely used in food and pharmacology research to investigate the release and absorption behavior of nutrients and drug components.
The TIM system consists of glass units for the stomach, duodenum, jejunum, and ileum. Each unit has a glass jacket with a flexible inner membrane to allow expansion and contraction of the walls. Pressures and the temperature of the water pumped through the glass jackets can be adjusted to simulate peristaltic contractions and body temperature. Peristaltic valves are used to connect each unit. Computer simulation controls the flow of the digested food through and between the compartments.
TIM, with its computer-controlled simulations of peristaltic contractions and membrane technologies, offers flexibility to be used for different groups (babies, adults, elderly, and animal species), including health and disease conditions. Even though TIM-1 and TIM-2 complement each other as the upper and lower sections of the gastrointestinal tract, they do not run jointly.
2. Simulator of the human intestinal microbial ecosystem (SHIME®)
Simulator of the human intestinal microbial ecosystem (SHIME®, Ghent University-Prodigest, Belgium) has been developed to simulate the microbial ecosystem of the gastrointestinal tract. The system that contains five reactor stages simulates the stomach, the small intestine, and the regions of the large intestine together. The first two reactors simulate the acidity and pepsin digestion of the stomach and digestive process of the small intestine by fill and draw principle, where the stomach was simulated by reactor 1, and the small intestine by reactor 2. Peristaltic pumps were used for the controlled transfer of the vessel contents and digestive juices. The last three vessels, which were stirred continuously with a magnetic stirrer, were used to simulate the sections of the large intestine, ascending, transverse, and descending colons. Transit time of the contents and pH values in the vessels can be controlled to mimic in vivo data. System temperature kept at 37 °C, and N2 is flushed every day for 15 min to secure anaerobic conditions.
The group has other new models for different purposes. M-SHIME® (Mucus-SHIME) contains a mucosal compartment integrated to the colonic regions of SHIME® to evaluate the fraction of microorganisms that can selectively adhere to the mucous layer that covers the gut wall and play an essential role as a barrier against pathogens.
Diseased conditions such as inflammatory bowel disease have also been simulated with specific protocols. This model’s strength is the incorporation of the human microbiota. However, it lacks the dialysis modules in the small and large intestines. Furthermore, using magnetic stirrers for mixing of the vessels is not as good as peristaltic movements.
3. Engineered stomach and small intestinal (ESIN) system.
Engineered stomach and small intestinal (ESIN) system have been developed at the University of Auvergne (Clermont-Ferrand, France). This dynamic system has been reported to aim to overcome some limitations of otherwise complex and useful models like TIM and SHIME.
This dynamic model includes a patented (WO2009087314 A1) design for the stomach section.
The ESIN model has six vessels, a meal reservoir, salivary container, the stomach, and the small intestine, duodenum, jejunum, and ileum segments. Food particles are advanced gradually into the stomach via the meal reservoir. Solid particles can pass the pylorus only if their sizes are reduced to 1–2 mm. The passage of the small particles and liquid into small vessel was achieved by indentation inside the stomach vessels. Solid particles larger than 2 mm stay in the gastric vessel for further digestion.
Source :
4. In vitro dynamic system (DIDGI ®)
This dynamic digestion system, which is developed at the French National Institute for Agricultural Research (INRA, Rennes, France) simulates the stomach and the small intestine with two glass jacketed vessels. The jackets are filled with water that is pumped from a temperature-controlled water bath. A Teflon membrane with 2 mm holes is placed before the transfer pump between the gastric and the intestinal compartment mimicking the sieving effect of the pylorus in humans. The temperature, pH, flow rate of the meal, digestive secretions and emptying rate for each compartment are controlled by computer simulation designed with the data obtained from in vivo observations.
Source : 3 Dynamic in vitro model of the large intestine (TIM-2). | Download Scientific Diagram (researchgate.net)
5. Simulator of the gastrointestinal tract (Simgi®)
This dynamic simulator has been developed to reproduce gastrointestinal digestion and colonic fermentation at the Institute of Food Science Research (Madrid, Spain). The simgi® model consists of five compartments simulating the stomach, small intestine, and the ascending, transverse, and descending colon. The stomach section has two transparent and rigid plastic vessels that cover a flexible silicone container. Water at 37°C pumped through the jacket between the plastic modules, and the flexible container is used to simulate peristaltic movements.
The system has collecting points in each of the compartments to carry out the biochemical and microbiological analysis. This system combines peristaltic contractions and chyme transit behaviour for gastric and small intestine compartments.
6. Dynamic gastric model (DGM)
The model (DGM) has been developed at the Institute of Food Research (Norwich, UK). This computer-controlled model (Table 2) simulating only the stomach can process real size chewed meals and simulates the physiological conditions such as mixing, the transit of meals, and forces observed in the stomach. This model simulates three stages of the in vivo conditions:
1. stage: the proximal stomach for ingestion and mixing;
2. stage: the antrum for higher shear rate;
3. stage: the duodenum, first part of the small intestine.
In the model, the disintegration of the food particles was obtained by a stationary outer and mobile inner tube. Temperature, transit time, and flow rates of acid, salts, and enzymes are controlled and adjusted to desired physiological rates. The model produces a cyclical (0.05 Hz) mixing in the body of the stomach and preferential antral sieving. In the system, with the collection of data obtained by the samples delivered from the antrum over time, emptying profiles, particle size reduction, and mass transfer data can be obtained but, peristaltic movement is not accurately simulated.
Conclusion
Many in vitro simulation tools have been designed to reproduce the complexity of the human digestive system. Many of them are very complex systems with their sometimes-in-house computer control and the mechanic or dynamic systems designs. They attempt to reproduce the physiological conditions of the human digestive system as close as possible by the use of observed in vivo data obtained from human subjects. They use complex computer control systems to adjust the dynamics of pH, transit time, and digestive secretions. Even though it was not possible to perfectly match the complex human digestive system, it was possible to simulate the digestive system’s critical mechanical, dynamic, and biochemical processes in a robust, repeatable manner. The models have been improved extensively over the years, and some have been used by the food, nutrition, and medical industry widely. Still, new models show up, as seen in a recent real-size stomach model developed
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