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Background and Purpose Chemotherapeutic agents, including 5-fluorouracil (5-FU), frequently cause intestinal mucositis resulting in severe diarrhoea and morphological mucosal damage. 5-HT3 receptor antagonists are clinically effective in the treatment of nausea and emesis during cancer chemotherapy. Therefore we here have examined the effects of 5-HT3 receptor antagonists on 5-FU-induced intestinal mucositis in mice. Experimental Approach Intestinal mucositis was induced in male C57BL/6 mice by daily administration of 5-FU (50 mg·kg−1) for 5 days. Effects of 5-HT3 receptor antagonists, ramosetron (0.01–0.1 mg·kg−1) and ondansetron (5 mg·kg−1), on the accompanying histology, cytokine production and apoptosis were assessed. Key Results Continuous administration of 5-FU to mice caused severe intestinal mucositis, which was histologically characterized by the shortening of villi and destruction of intestinal crypts, accompanied by body weight loss and diarrhoea. Daily ramosetron administration dose-dependently reduced the severity of intestinal mucositis, body weight loss and diarrhoea. Similar beneficial effects were observed with ondansetron. The number of apoptotic, caspase-3- and caspase-8-activated cells increased 24 h after the first 5-FU administration, and these responses were reduced by ramosetron. The up-regulation of TNF-α, IL-1β and IL-6 following 5-FU treatment was also attenuated by ramosetron. Conclusions and Implications 5-HT3 receptor antagonists ameliorated 5-FU-induced intestinal mucositis in mice, and this action could result from suppression of apoptotic responses in the intestinal crypt cells via inhibition of cytokine expression. Thus, 5-HT3 receptor antagonists may be useful for preventing not only nausea and emesis but also intestinal mucositis during 5-FU chemotherapy.

We have reported that nicotine and the specific α7AChR agonist ameliorate indomethacin-induced intestinal lesions in mice by activating α7 nicotinic acetylcholine receptors (α7nAChR). Dopamine D2–receptor antagonists, such as domperidone and metoclopramide, enhance the release of ACh from vagal efferent nerves. The present study examined the effects of domperidone and metoclopramide on indomethacin-induced small intestinal ulceration in mice, focusing on the α7AChR. Male C57BL/6 mice were administered indomethacin (10 mg/kg, s.c.) and sacrificed 24 h later. Domperidone (0.1 – 10 mg/kg) and metoclopramide (0.03 – 0.3 mg/kg) were administered i.p. twice, at 0.5 h before and 8 h after indomethacin treatment, while methyllycaconitine (a selective antagonist of α7nAChR, 30 mg/kg) was administered twice, at 0.5 h before each domperidone treatment. Indomethacin caused severe hemorrhagic lesions in the small intestine, mostly to the jejunum and ileum, with a concomitant increase in myeloperoxidase (MPO) activity. Domperidone suppressed the severity of lesions and the increase in MPO activity at low doses (0.1 – 3 mg/kg), but not at a high dose (10 mg/kg). Similar effects were also observed by metoclopramide. The protective effects of domperidone and metoclopramide were totally abolished by prior administration of methyllycaconitine. Indomethacin treatment markedly enhanced inducible nitric oxide synthase and chemokine mRNA expression in the small intestine, but these responses were all significantly attenuated by either domperidone or metoclopramide. These findings suggest that dopamine D2–receptor antagonists ameliorate indomethacin-induced small intestinal ulceration through the activation of endogenous anti-inflammatory pathways mediated by α7nAChR. Keywords:: dopamine D2–receptor antagonist, α7 nicotinic acetylcholine receptor, indomethacin, small intestinal ulceration, chemokine

vomiting (4), diarrhea (4) and mucositis oral (2) respectively. Twelve patients had gastrointestinal toxicities (Grade 2-4) and 4 patients had no toxicities. The serum DAO activity of 12 symptomatic patients were 4.7±2.4U/L before chemotherapy, 3.5±1.5U/L during chemotherapy (day 9) and 3.6±1.3U/L after drug holiday (day 21) respectively. The DAO activity during chemotherapy decreased significantly (p=0.006) compared to the value before chemotherapy and recovered after drug holiday. The % decrease of DAO activity during chemotherapy was 25.5% in symptomatic patients (p=0.006) and not significant in no symptomatic patients compared to the value before chemotherapy. The gastrointestinal toxicities due to anticancer drugs appeared 9 days after the administration of anticancer drugs and the decrease of serum DAO activity was detected early before appearance of the symptoms. [Conclusion]Our results suggested that the serumDAO activity showed early and quantitative gastrointestinal toxicities and was useful as an indicative marker for intestinal mucosal damage.