Dextran sulfate sodium-induced inflammation and colitis in mice are ameliorated by (R)-ketamine, but not (S)-ketamine: A role of TrkB signaling.

Ulcerative colitis (UC) is a chronic inflammatory bowel disease that causes long-lasting inflammation and colitis in the gastrointestinal tract. Depression is a common symptom in patients with UC. (R)-ketamine is a new safer antidepressant than (R,S)-ketamine and (S)-ketamine. Here, we examined the effects of two ketamine enantiomers on the dextran sulfate sodium (DSS)-induced colitis model of UC. Ingestion of 3% DSS in drinking water for 14 days increased the scores of Disease Activity Index (DAI) in mice. Repeated administration of (R)-ketamine (10 mg/kg/day, 14 days or last 7 days), but not (S)-ketamine (10 mg/kg/day, 14 days or last 7 days), significantly ameliorated the increased DAI score and increased blood levels of interleukin-6 (IL-6) in DSS-treated mice. In addition, (R)-ketamine, but not (S)-ketamine, attenuated the reduced colonic length in DSS-treated mice. Furthermore, DSS-induced increased DAI score and blood IL-6 levels were significantly ameliorated after subsequent repeated administration of (R)-ketamine (10 mg/kg/day for last 7 days), but not 5-aminosalicyclic acid (50 mg/kg/day for last 7 days). Moreover, the pretreatment with a tropomyosin-receptor-kinase B (TrkB) antagonist ANA-12 (0.5 mg/kg) significantly blocked the beneficial effects of (R)-ketamine in DSS-induced UC model. The study shows that (R)-ketamine can produce beneficial effects in DSS-induced colitis model through TrkB stimulation. Therefore, (R)-ketamine may be a novel therapeutic drug for inflammatory bowel diseases such as UC.