TRPV1 antagonism and genetic deletion attenuate inflammation and referred hyperalgesia associated with oxazolon colitis in mice

Jin Kyu Choi, Il-Hong Bae, Young-Ho Park, Kyung-Min Lim. AMOREPACIFIC Co. R&D Center, Medical Beauty Research Institute, Republic of Korea

Transient receptor potential vanilloid type 1 (TRPV1) expressing sensory neurons are distributed throughout the whole gastrointestinal tract. Recent studies reported that TRPV1 increases in the colon with ulcerative colitis (UC) and is involved in the pathogenesis of UC. In this study, we investigated the effects of a novel TRPV1 antagonist, PAC-14028 ((E)-N-[(R)-1-(3,5-difluoro-4-methanesulfonylamino-phenyl)-ethyl]-3-(2-propyl-6-trifluoromethyl-pyridine-3-yl)-acrylamide), and TRPV1 gene knock-out in murine oxazolone colitis model that resembles human UC.

Colitis was induced by intrarectal administration of 0.075% oxazolone (in 50 % ethanol, 0.15 ml/mice) under isoflurane anesthesia in wild type female C57BL/6J mice (18-21 g) and TRPV1 knockout (-/-) mice (18-21 g). Vehicle, PAC-14028 (3-30 mg/kg), and sulfasalazine (300 mg/kg) were administered by oral gavage once a day from one day prior to oxazolone administration until the sacrifice of the mice. The mice were sacrificed on day 3 and colitis was evaluated by disease activity index, colon length, and colon weight. The disease activity index (DAI) was calculated with diarrhea, bloody stool and body weight. The threshold of referred hyperalgesia in oxazolone colitis model was measured with the application of von Frey hairs on the abdomen of mice. All data were analyzed by one way analysis of variance (ANOVA) followed by post-hoc test or Student’s t-test to determine treatment effect and to compare differences between group means.

Intrarectal administration of oxazolone induced robust colitis as shown by the increased DAI, colon contraction, and colon weight increase. In contrast, oxazolone-induced colitis was significantly (p<0.05) attenuated by oral administration of TRPV1 antagonist PAC-14028 (30 mg/kg) as demonstrated by the alleviation of disease severity, colon contraction, and colon weight increase. TRPV1 gene knock-out and sulfasalazine (300 mg/kg) also manifested a significant protection against oxazolone-induced colitis.

As to the abdominal pain associated with oxazolone-induced colitis, the threshold of referred hyperalgesia was reduced by oxazolone injection. Meanwhile, PAC-14028 (30 mg/kg)-treated mice and TRPV1 knockout mice showed the significant analgesic effect against referred hyperalgesia when compared with vehicle-treated mice. But sulfasalazine (300 mg/kg)-treated mice failed to show significant analgesic effect.

These results demonstrated that TRPV1 antagonism can alleviate UC-associated inflammation and abdominal pain in oxazolone-induced colitis model, reflecting that the TRPV1 antagonist might be a promising drug for the treatment of UC.