$$\rightleftharpoonup{xx}$$
$$\longleftharp{xx}$$,
$$\longrightharp{xx}$$,
Male and female IL-10-KO mice develop enterocolitis after a short exposure to a piroxicam-fortified diet (Figure 1A–E). By day 2, piroxicam-exposed mice exhibited statistically significantly greater weight loss than their same-sex regular chow-fed controls, and comparable weight loss was observed across sexes (Figure 1B). Apparent daily food intake remained unchanged throughout piroxicam exposure and enterocolitis development and resembled intake of standard chow, indicating that weight loss in this model is not primarily driven by reduced intake but rather by other factors that promote metabolic expenditure (Figure 1C).
To further investigate the progression of intestinal inflammation, disease activity was assessed by a combined score of weight loss, blood in stool, stool consistency, and degree of rectal prolapse. The modified disease activity index (DAI) was assessed at baseline and day 7; day 7 scores are shown in Figure 1D. In addition, the development of enterocolitis observed in piroxicam-exposed mice was associated with a strong trend toward increased mortality, although this difference was not statistically significant (p = 0.12; Figure 1E). In this model, early mortality is secondary to mice reaching humane endpoints (weight loss > 20%) and preferentially affects males (Figure 1E). If mortality is a sought-after experimental endpoint, a larger number of experimental animals than used here may be considered. In this study, the authors used the minimum number of animals necessary to achieve statistical power through study completion, accounting for expected mortality.
Colon shortening is a feature associated with the severity of colitis in murine models. At harvest, both male and female IL-10-KO mice fed a piroxicam diet had shorter colons than those fed regular chow (Figures 2A–B). Upon histological assessment, colons from the piroxicam-fed group showed epithelial damage and increased immune cell infiltration, changes associated with colitis (Figure 2C). These findings translated into a higher histological score (Figure 2D). Additionally, transcriptional levels of pro-inflammatory cytokines involved in human IBD and murine models of colitis were evaluated23. In agreement with prior reports, colons from piroxicam-fed IL-10-KO mice displayed a significant upregulation of pro-inflammatory cytokines at the transcript level (Figure 3A–D). Of note, this transcriptional change was not observed in IL-10-KO mice receiving regular chow or WT mice receiving piroxicam-fortified diet, indicating that the transcriptional signature was driven by a combination of IL-10 deficiency and piroxicam, rather than either factor alone. Finally, the authors confirmed that the transcriptional signature observed in the colon from piroxicam-treated mice was associated with increased calprotectin staining in the colonic mucosa (Figure 3E)24,25.

Figure 1: Piroxicam-accelerated enterocolitis in IL-10-KO mice. (A) Schematic overview of experimental protocol. (B) Body weight, (C) food intake, (D) day 7 disease activity index (DAI), (E) survival curve in 8-week-old male and 8-week-old female IL-10-KO mice receiving a piroxicam-fortified diet or a regular diet. Male control: n = 5, male piroxicam: n = 5, female control: n = 6, female piroxicam: n = 6 in (B), (C), and (D). Male control: n = 6, male piroxicam: n = 10, female control: n = 6, female piroxicam: n = 7 in (E). * p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.001 by pairwise comparison of male (top asterisks) and female (bottom asterisks) mice in (B). Statistical analyses were performed using a two-tailed unpaired t-test in (B), (C), and (D), and a log-rank test in (E). Mean values and error bars representing the standard error of the mean (SEM) are depicted. In bar charts, individual measurements are depicted by jitter plots. Please click here to view a larger version of this figure.

Figure 2: Colon shortening and histological assessment. (A) Representative colon specimens from 8-week-old male and female interleukin-10-knockout (IL-10-KO) mice receiving a piroxicam diet (top) or a regular diet (bottom) for 7 days. Scale bar = 1 cm. (B) Colon length on day 7 (male control: n = 5, male piroxicam: n = 5, female control: n = 6, female piroxicam: n = 6). (C) Representative images of HE-stained colon. Scale bar = 100 µm. (D) Histology score on day 7. Two-tailed unpaired t-test in (B) and (D). Mean values and error bars representing SEM are depicted. In bar charts, individual measurements are depicted by jitter plots. Not significant (NS), * p ≤ 0.05, *** p ≤ 0.001, **** p ≤ 0.0001 by pairwise comparison. Please click here to view a larger version of this figure.

Figure 3: Inflammatory changes in piroxicam-accelerated enterocolitis. Quantitative RT-PCR results of (A) Tnf, (B) Il6, (C) Il1b, and (D) Ifng in colonic tissue from 8-week-old wild-type (WT) and interleukin-10-knockout (IL-10-KO) male mice at the time of harvest. For panels A–D, WT piroxicam n = 7, KO piroxicam n = 6, KO control n = 3. (E) Representative calprotectin immunofluorescence staining of colonic tissue of 8-week-old IL-10-KO mice at the time of harvest. Statistical analyses were performed using a two-tailed unpaired t-test. Mean values and error bars representing the standard error of the mean (SEM) are depicted. In bar charts, individual measurements are depicted by jitter plots. Scale bar in (E) = 200 µm. Not significant (NS), * p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.001 by pairwise comparison. Please click here to view a larger version of this figure.
| Domain | Score |
| Weight | 0 – Unchanged |
| 1 – Loss of 1–5% |
| 2 – Loss of 6–10% |
| 3 – Loss of 11–20% |
| 4 – ; Greater than 20% loss |
| Stool Consistency | 0 – Normal ; |
| 1 - Soft but formed |
| 2 – Loose stools (not watery) |
| 4 – Diarrhea (liquid stool) |
| Bleeding | 0 – None |
| 2 – Hematooccult positive stools |
| 3 – Visible blood on stool |
| 4 – Gross bleeding per rectum |
| Rectal Prolapse | 0 – Absent |
| 1 – Present |
| Total Score | Total Score: Sum of (Domain scores) for each domain |
Table 1: Disease activity score (DAI). A scoring system to determine disease activity by weight loss, stool consistency, blood in stool, and rectal prolapse. Adapted from Sifuentes-Dominguez, et al26.
| Tissue Damage | | Lamina Propria Inflammatory Cell Infiltration |
| Features | Involvement | | Features | Involvement |
| 0 | None | 1 | 1–25% of surface | | 0 | Infrequent | 1 | 1–25% of surface |
| 1 | Infrequent ; | 2 | 26–50% of surface | | 1 | Increased, some neutrophils | 2 | 26–50% of surface |
| 2 | Mucosal erosions and ulcerations | 3 | 51–75% of surface | | 2 | Submucosal presence of inflammatory cell clusters | 3 | 51–75% of surface |
| 3 | Extensive damage deep into the bowel wall | 4 | 76–100% of surface | | 3 | Transmural cell infiltrations | 4 | 76–100% of surface |
Table 2: Histologic scoring system. Scoring system to determine histologic changes and damage. Adapted from Sifuentes-Dominguez, et al26.