Animal Models of Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a chronic intestinal inflammatory condition that is mediated by genetic, immune, and environmental factors. Due to its long-term, relapsing course, IBD can result in repeated cycles of mucosal damage and repair, potentially increasing the risk of colorectal cancer over time. While current treatments focus on reducing inflammation, they are less effective in addressing long-term complications such as fibrosis-related intestinal strictures. The development of new therapeutics to treat long-term complications of IBD remains a significant unmet medical need.

PART 1: Introduction

An autoimmune disease occurs when the immune system malfunctions and mistakenly attacks the body’s own healthy tissues, failing to recognize them as “self” and treating them as foreign invaders. There are over 100 types of autoimmune diseases, including Rheumatoid Arthritis (RA), Systemic Lupus Erythematosus (SLE), and Multiple Sclerosis (MS). IBD affects an estimated 6–8 million people worldwide. According to Evaluate Pharma, the global IBD drug market is expected to reach $28 billion by 2028, accounting for 20% of the overall autoimmune drug market. ^[1]

IBD is typically classified into two main types: Ulcerative Colitis (UC) and Crohn’s Disease (CD). UC primarily affects the colon and is generally limited to the mucosal and submucosal layers, while CD can involve any part of the gastrointestinal tract, including both the small intestine and the colon. CD is characterized by deeper inflammation that can penetrate the intestinal wall, leading to complications such as strictures and fibrosis, extending from the mucosal layer to the muscular and serosal layers. (Figure 1).

Figure 1. Crohn’s Disease vs Ulcerative Colitis ^[2-3]

Although the exact cause of IBD remains unknown, current research suggests that it results from a complex interplay of genetic predisposition, environmental factors, abnormal immune response, and disruptions in the composition of gut bacteria, essentially creating an imbalance within the gut microbiome that leads to inflammation in the intestines. High-fat diet, stress, and the overuse of antibiotics may further accelerate dysbiosis within the gut ^[4] (Figure 2).

Figure 2: Disruption of gut homeostasis ^[4]

In addition to the imbalance in gut homeostasis, immune dysregulation is a significant cause of IBD pathogenesis. Two types of immune cells are essential ^[5] (Figure 3):

1. Innate lymphoid cells (ILCs): including ILC-1, 2, 3, and Natural Killer (NK) cells.
2. Adaptive immune cells: such as T cells (especially Th1, Th2, and Th17 subsets), B lymphocytes, dendritic cells, macrophages, and neutrophils.

These immune cells release pro-inflammatory cytokines, such as Interleukin-33 (IL-33), IL-36, Tumor Necrosis Factor-α (TNF-α), and Interferon-γ (IFN-γ), which exacerbate inflammation and contribute to intestinal fibrosis. Excessive deposition of the extracellular matrix (ECM) can lead to the development of intestinal strictures, fibrosis, and, in severe cases, intestinal obstruction.

Figure 3. Aberrant immune response in IBD ^[5]

PART 2: Animal Models for IBD

Currently, animal models play a pivotal role in studying the pathogenesis, drug efficacy, and pharmacological mechanisms of IBD, with a predominant focus on elucidating the interplay between mucosal epithelium, intestinal microorganisms, and immunity. WuXi Biology has established a variety of IBD animal models (Figure 4), including:

• Chemically-induced models: Dextran Sulfate Sodium (DSS) and Oxazolone (OXZ) induction to mimic UC, and 2,4,6-Trinitrobenzene Sulfonic Acid (TNBS) induction to mimic CD;
• Adoptive T-cell transfer induced models to mimic Crohn’s disease;
• Anti-CD40 induced T-cell-independent IBD model to mimic UC;
• Engineered spontaneous colitis models in IL-10-/- and Foxp3-/- mice to mimic CD

Figure 4. Animal models for IBD at WuXi Biology

Additionally, pharmacological validation of therapeutics against popular drug targets, such as JAK inhibitors, TNF-α antibodies, S1P1 receptor inhibitors, and IL-6/18 antibodies, has been performed using these models. WuXi Biology offers one-stop preclinical services for IBD pharmacology studies (Figure 5) including:

• IBD model selection tailored on therapeutic targets for your test articles （Figure 5A）
• In-life studies with IBD models, including body weight changes, disease activity index (DAI) scores, and collection of colon parameter data Figure 5B）
• Histopathological analysis and pathological scoring of colon samples （Figure 5B）
• Immunological analysis, such as inflammatory cell subtypes and inflammatory cytokines （Figure 5C）
• Inflammatory pathways and multi-factor omics studies analysis （Figure 5D）

Figure 5. One-stop preclinical services for IBD at WuXi Biology

PART 3: Case Studies

3.1 DSS-Induced Acute/Chronic Colitis

1. DSS-induced acute colitis model: Mice are exposed to DSS free drinking in water for 7 days to disrupt intestinal epithelial cells and induce inflammation. The model is validated by assessing body weight changes, DAI variations, and histopathological changes (Figure 6A).
2. DSS-induced chronic colitis model: Mice are exposed to 4 cycles of DSS and distilled water at 4 day-on-3 day-off interval to induce chronic inflammation in the bowel. This model is validated by measuring body weight changes and DAI scores (Figure 6B).

Figure 6. DSS-induced acute/chronic colitis models

3.2 T-Cell Transfer Induced Colitis Model

In developing this model, WuXi Biology begins by isolating CD4⁺CD45RB^high T cells from donor mouse spleens using magnetic beads separation and flow cytometry. These purified T cells are then transferred into recipient SCID mice (Figure 7A). Colitis progression is monitored by tracking changes in body weight and DAI scores, both of which help assess the severity of the disease (Figure 7B).

Figure 7.  A. Scheme and FACS gating strategy of T cell transfer induced colitis in SCID mice; B. In-life study (Body weight change and DAI score) in SCID mice

Conclusion:

IBD animal models are crucial for studying disease progression, understanding underlying mechanisms, and identifying novel therapeutic targets. Advances in new modalities and ongoing research into pathogenesis are accelerating drug development in IBD.

References:

[1] https://www.evaluate.com/

[2] Digestive Medicine Research 4 (2021): n. pag. Web. 9 Jul. 2024

[3] Trends Mol Med. 2023 Mar;29(3):241-253.

[4] Experimental & Molecular Medicine (2017) 49, e338;

[5] Inflamm Intest Dis. 2023;7(3-4):119-127.

[6] http://www.phirda.com/artilce_35551.html&module=trackingCodeGenerator

[7] Nat Rev Drug Discov 23, 546–562 (2024).

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