In vitro Models of the Small Intestine for Studying Intestinal Diseases

Abstract

The small intestine is a digestive organ that has a complex and dynamic ecosystem, which is vulnerable to the risk of pathogen infections and disorders or imbalances. Many studies have focused attention on intestinal mechanisms, such as host–microbiome interactions and pathways, which are associated with its healthy and diseased conditions. This review highlights the intestine models currently used for simulating such normal and diseased states. We introduce the typical models used to simulate the intestine along with its cell composition, structure, cellular functions, and external environment and review the current state of the art for in vitro cell-based models of the small intestine system to replace animal models, including ex vivo, 2D culture, organoid, lab-on-a-chip, and 3D culture models. These models are described in terms of their structure, composition, and co-culture availability with microbiomes. Furthermore, we discuss the potential application for the aforementioned techniques to these in vitro models. The review concludes with a summary of intestine models from the viewpoint of current techniques as well as their main features, highlighting potential future developments and applications.

Gut-on-a-chip for disease models

“…Mucus consists of water and glycosylated proteins, termed as mucins, which are O-linked glycan-attached glycoproteins anchored to the intestinal epithelial layer. 40 The lamina propria contains many immune cells ( Figure 1 ), including macrophages and dendritic cells. 34 …”

“…The intestinal microbiota interacts directly with the host by producing a diverse reservoir of metabolites obtained from exogenous or endogenous substances. 40 Many intestinal diseases are associated with a decreased diversity of the intestinal microbiota. However, aberrant intestinal microbiota are not only associated with intestinal diseases, such as Crohn’s disease and ulcerative colitis, but also with non-intestinal diseases, such as obesity, type 2 diabetes mellitus, rheumatoid arthritis and neurological and psychiatric disorders.…”

Gut-on-a-chip models for dissecting the gut microbiology and physiology

“…The eminent role of the gut in health and diseases has aroused tremendous interest among the scientific community in deciphering the gut's physiological complexities over the past decades; however, one of the major stumbling blocks in these attempts has been the limitations of conventional experimental techniques. 18 Among various methods, direct experimentation on human subjects has been proven to be difficult due to the inaccessibility of the GI tract, and imaging techniques such as colonoscopy have been invasive and lacked cellular-level resolution. 19–21 Analyzing the human microbiome has been conducted by sequencing fecal samples, but these are not representative of the entire gut microbial population, as many bacteria live in hardly accessible zones in the form of surface-attached communities, termed biofilms, inside the intestine.…”

Development and Characterization of an In Vitro Intestinal Model Including Extracellular Matrix and Macrovascular Endothelium

“…They also create well-controlled and reproducible conditions for evaluating cell responses. 13 Most two-(2D) and three-dimensional (3D) in vitro intestinal models comprise two main cell types, i.e., enterocytes (Caco-2 cells) and mucusproducing goblet cells (HT29-MTX cells), which are usually cultured for 21 days to achieve a confluent and fully differentiated cell model. 14 Some more complex models also consider M cells, which account for approximately 10% of the epithelial cells and are a key player in phagocytosis and transcytosis of luminal macromolecules and antigens.…”