DSS-Induced Colitis

Reagents and chemicals

• DSS is dissolved in drinking water to induce colitis; published mouse protocols and studies commonly report acute DSS exposure for about 5–7 days, with concentrations varying by strain, age, DSS lot, and disease-severity target, including 1–5% DSS in protocol literature and 2.5–4% DSS in comparative C57BL/6 studies^[1][2][4][8].

• Phosphate-buffered saline or vehicle drinking water is used for control animals, formalin or other histology fixatives are used for colon tissue fixation, and hematoxylin–eosin staining is used to evaluate mucosal inflammation, epithelial injury, crypt damage, and ulceration^{[1][2][9][10]}.

Antibodies, probes, dyes, or kits

• FITC-dextran is used as an intestinal permeability tracer in DSS-colitis studies, and cytokine assays such as IL-1β ELISA have been used to quantify inflammatory responses in colon tissue^[4][7].

• Antibodies or assays for tight-junction proteins such as ZO-1, occludin, and claudin-1, inflammatory cytokines such as TNF-α, IL-6, IL-17, and IFN-γ, and myeloperoxidase activity are used when the experimental question requires barrier or inflammatory-pathway readouts^[4][6][7][8].

Equipment and instruments

• Animal scales are used for daily body-weight monitoring, gross dissection tools are used to collect and measure colon length, histology equipment is used for fixation, embedding, sectioning, and H&E staining, and microscopy or digital slide imaging is used to score mucosal injury and ulceration^{[1][2][4][9][10]}.

• ELISA readers, qPCR instruments, Western blot equipment, fluorescence microscopes, and permeability-assay equipment are used only when cytokine, gene-expression, protein-expression, tight-junction, or FITC-dextran permeability endpoints are included^{[4][6][7][8][11]}.

Preparation Steps

• Use age-, sex-, strain-, and housing-matched mice, assign a water-control group and a DSS group, and select DSS concentration and exposure duration based on pilot severity or published conditions because disease severity varies with experimental conditions^[1][2][4][8].

• Prepare fresh DSS drinking solution at the literature-supported target concentration, provide it ad libitum for the selected induction period, and record baseline body weight before DSS exposure because weight change is a core component of clinical scoring^[1][2][4][8].

Operation Steps

• Administer DSS in drinking water for the planned induction period; commonly cited acute protocols use several days of DSS exposure, including 5–7 days in protocol and temporal studies, while comparative C57BL/6 work tested 2.5% and 4% DSS and sacrificed mice on day 7^[1][2][4][8].

• Monitor mice daily for body weight, stool consistency, and fecal blood, and calculate disease activity index from these clinical variables when using a DAI-based design^[1][4][8].

• At the experimental endpoint, euthanize animals according to the approved animal protocol, excise the colon, measure colon length, collect the distal or descending colon for histology when a site-specific histologic endpoint is planned, and reserve additional tissue for cytokine, RNA, protein, MPO, or permeability-related assays as required by the study design^{[1][2][4][6][7][8]}.

• For histology, fix colon tissue, process and stain sections with H&E, and evaluate inflammatory infiltrate, epithelial changes, crypt architecture, erosions, ulceration, and tissue damage using a predefined scoring system or whole-colon image-analysis approach^[2][9][10].

Data Acquisition and Analysis

• Interpret successful DSS colitis as concordant worsening of clinical signs and tissue injury, including increased DAI, body-weight loss, diarrhea or bleeding, shortened colon length, histologic injury, increased inflammatory markers, increased permeability, or altered tight-junction readouts, depending on the endpoints included^{[1][2][4][6][7][8]}.

• Use water-treated mice as negative controls, DSS-treated mice as disease-model controls, and blinded histologic scoring or objective image analysis when possible; Park et al. reported that DAI was useful for measuring inflammation and that the descending colon was more appropriate than ascending colon for histologic evaluation in their DSS comparison study^[4][9][10].

• For qPCR from DSS-exposed colon tissue, interpret RNA results cautiously because DSS contamination can inhibit reverse transcriptase and DNA polymerase activity; lithium chloride purification or poly-A purification has been reported to reduce DSS-related qPCR inhibition^[11][12].

Problem: DSS-treated mice show weak or inconsistent clinical colitis.

• Possible Cause: DSS concentration, exposure duration, age, strain, or other experimental variables may be insufficient for the intended severity.
• Literature-supported Solution: Use a pilot or published matched condition, because comparative work found stronger DAI in nine-week mice receiving 4% DSS than in younger mice, and protocol literature emphasizes that acute and chronic DSS regimens vary by design^[1][4][8].

Problem: Histology does not match clinical disease severity.

• Possible Cause: Sampling only a limited or less affected colon region can miss spatially variable injury.
• Literature-supported Solution: Include distal or descending colon assessment and consider whole-colon longitudinal image analysis, because Park et al. found higher histologic scores in descending than ascending colon and Garcia-Hernandez et al. used whole-colon injury and ulceration quantification to reduce biased sampling^[4][10].

Problem: qPCR shows poor amplification or inconsistent reference-gene Cq values from DSS-colon samples.

• Possible Cause: DSS carried into RNA preparations can inhibit reverse transcriptase and Taq polymerase activity.
• Literature-supported Solution: Add lithium chloride purification or poly-A purification before RT-qPCR, as these approaches reduced DSS-associated qPCR interference in published studies^[11][12].