Abstract:

Objective To compare female C57BL/6J and BALB/c mice models of ulcerative colitis (UC) induced by dextran sulfate sodium salt (DSS), providing a reference for selecting female animal models in studies of innovative drugs for UC treatment. Methods A total of 48 female mice aged 6–8 weeks, including 24 C57BL/6J and 24 BALB/c mice, were divided into four groups: control group, UC-3d group (2.5% DSS drinking for 3 days), UC-7d group (2.5% DSS drinking for 7 days), and UC-withdrawal group (2.5% DSS drinking for 7 days followed by 3 days of pure water replacement), with 6 mice in each group. Body weight, fecal occult blood, and stool characteristics were recorded daily, and disease activity index (DAI) scores were calculated. At the end of DSS induction, mice were gavaged with fluorescein isothiocyanate (FITC)-labeled dextran solution before tissue collection. Four hours later, under deep anesthesia induced by inhalation of 4% isoflurane, blood samples were collected from the retro-orbital venous plexus, and euthanasia was performed by cervical dislocation. The colon was then separated immediately, and its length from the anus to the ileocecal junction was measured. Colon tissues were fixed, embedded, and sectioned, and they were evaluated using hematoxylin-eosin (HE) staining and alcian blue-periodic acid-Schiff (AB-PAS) staining to comprehensively assess the degree of colonic inflammation. The spleen was also collected and weighed, and the spleen coefficient was calculated. Serum FITC fluorescence intensity and D-lactic acid concentration were measured to evaluate intestinal permeability and barrier injury. The grooming duration, the number of buried marbles, the time spent in the center of the open field, and the total distance traveled were measured to evaluate anxiety/depression-like behaviors in mice. Results Fecal occult blood appeared in both C57BL/6J and BALB/c mice after 3 days of ad libitum access to DSS. Compared with the control group, there was no significant change in the weight loss rate of female BALB/c mice in the UC-7d and UC-withdrawal groups (P > 0.05), but the DAI score increased (P < 0.01). Conversely, both the weight loss rate and DAI score increased for female C57BL/6J mice in the UC-7d and UC-withdrawal groups (P < 0.01). In female C57BL/6J mice, both the UC-7d and UC-withdrawal groups had higher spleen coefficients than the control group (P < 0.05). Additionally, in these groups, colon length was significantly reduced (P < 0.01), FITC fluorescence intensity in serum was markedly increased (P < 0.01), obvious inflammatory reaction areas appeared in the colon, and the goblet cells and acidic mucus layer were damaged. In contrast, in female BALB/c mice, no significant differences were observed in colon length, serum FITC fluorescence intensity, or D-lactic acid concentration between the UC-7d and UC-withdrawal groups compared with the control group (P > 0.05). Only a few inflammatory cells and damaged goblet cells were observed in the colonic mucosal layer, and no other obvious pathological changes were detected. In addition, female C57BL/6J mice in the UC-7d group showed a significantly reduced total distance in the open field and fewer buried marbles (P < 0.05), indicating depression-like behavior, as well as prolonged grooming duration (P < 0.05), indicating anxiety-like behavior. Conclusion Female BALB/c mice are not sensitive to 2.5% DSS and do not show typical colonic pathological changes of UC. In contrast, ad libitum access to 2.5% DSS for 7 days successfully induces typical UC pathological symptoms and colonic pathological changes in female C57BL/6J mice. These changes persist for 3 days after DSS withdrawal, and the mice also exhibit symptoms of anxiety/depression. The results suggest that this model can be used for research on the pathogenesis and therapeutic drugs of UC.

Key words: Dextran sulfate sodium salt, Ulcerative colitis, Histopathological changes, Anxiety/depression-like behaviors, C57BL/6J mice, BALB/c mice