# (-)-Fenchone Ameliorates TNBS-Induced Colitis
## 3 Discussion  
UC is characterized as a non-transmural inflammation, that is, the inflammatory process normally does not affect the full thickness of the intestinal wall, remaining restricted to the mucosa and submuc. The inflammatory pattern tends to be symmetrical, continuous, and diffuse [7]. In the absence of timely and effective treatment, progressive and cumulative intestinal injury can lead to complications such as strictures, fistulas, loss of intestinal function, surgical interventions, and cancer [2, 27]. The experimental model used was the chemical one, using TNBS, which mimics inflammatory events in humans from the induction of T cell reactivity [28]. TNBS administration induces transmural colitis that is driven by a TH1-mediated immune response, which is characterized by the infiltration of CD4\({}^{+}\) cells, neutrophils, and macrophages into the lamina propria and the secretion of cytokines [29, 30]. The model employs intrarextal administration of TNBS hapten, solubilized in ethanol, which breaks the protective colonic mucus barrier, allowing the hapten to penetrate the lamina propria. TNBS will then haptenize the self or microbial proteins/peptides, making them immunogenic, and triggering both innate and adaptive immune responses in the host [28, 29, 31]. Additionally, the TNBS-induced model can mimic the acute and chronic stages of IBD [30]. In the acute model, (-)-fenchone, at the doses evaluated (37.5, 75, 150, and 300 mg/kg), significantly reduced (\(p<0.05\); \(p<0.001\)) ulcerative lesions when compared to colitic, with a significant reduction in diarrhea and in the severity and extent of the lesion which was reflected in the macroscopic lesion score. Diarrhea is an important parameter for evaluating the intestinal anti-inflammatory effect since its increase indicates a loss of the absorptive capacity of the colon [32]. In addition, reports in the literature demonstrate an association between diarrhea and epithelial barrier dysfunction, which occurs through failures in the integrity of gap junctions [33]. The histomorphological evaluation of tissues from rats subjected to (-)-fenchone treatment showed decreased lesion area and inflammatory infiltrate. Similar effects were previously found for monoterpenes \(p\)-cymene [34] and geraniol [35]. Figure 14: Photomicrographs with immunohistochemical marking for zonula occludens 1 (ZO-1) in the colon samples from the sub-chronic phase with recurrence of the intestinal inflammatory process in the TNBS-induced colitis model in rats. Non-colitic (**A**); colitic (5% Tween 80) (**B**); prednisolone (2 mg/kg) (**C**); (-)-fenchone (150 mg/kg) (**D**). Results are expressed as the median (minimum-maximum) of the parameters analyzed (n = 5, 3 sessions per animal). Kruskal-Wallis test and Dunn’s posterior test were performed using the software Graph Pad Prism 6. ***\(p<0.001\) compared to the colitic group (5% Tween 80). Given the promising results obtained in the acute model of ulcerative colitis, the best dose (150 mg/kg) was selected to investigate its effect in the 21-day chronic ulcerative colitis model with recurrence on the 14 th day and to investigate the antioxidant and immunomodulatory effect of (-)-fenchone. The relapsing ulcerative colitis model is considered to mimic this disease in humans and can be used to evaluate new treatments potentially applicable to IBD [36]. In the chronic model with recurrence of the inflammatory process, (-)-fenchone (150 mg/kg) significantly reduced (\(p\) < 0.001) ulcerative lesions when compared to the colitig group, with a significant reduction in the severity and extent of the lesion, in the weight/weight ratio, length, and macroscopic score of the lesion, thus evidencing the anti-inflammatory effect of the administration during 21 days of treatment. The weight/length ratio is a parameter for evaluating the inflammatory effect, in which the increase in this ratio in the colonic tissues is associated with the respective increase in edema, one of the first markers of inflammation [37].