Background: The pathogenesis of inflammatory bowel disease (IBD) is complex, and a useful therapeutic marker has not been proposed, yet. The role of PI3K/Akt pathway, however, is highlighted and suggested as a target for IBD therapy. Previously, we showed that 6-amino-2,4,5-trimethyl-pyridin-3-ols significantly inhibited angiogenesis induced by VEGF and serotonin. The structure-activity relationship and dose-dependency in antiangiogenic activity of the pyridinol derivatives clearly suggest that the compounds inhibit the common target molecule involved in both VEGF and serotonin signaling such as phosphoinositide-3-kinase (PI3K)/Akt. In the present study, we examined whether 6-amino-2,4,5-trimethyl-pyridin-3-ols suppress intestinal inflammation.
Methods: Based on the notion that IBD is of complex etiology, we tried a phenotype-based primary screening to inhibit the pathological action of TNF-α, instead of conducting a specific target-based approach to directly target TNF-α molecule. The anti-inflammatory activity in vitro was measured as an inhibitory activity against TNF-α-induced adhesion of monocytes to HT-29 human colonic epithelial cells. In order to demonstrate in vivo efficacy, some compounds were tested in the rat model of 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced colitis, a widely used animal model of IBD.
Results: We synthesized 6-amino-2,4,5,-trimethylpyridin-3-ols and tested them in colitis models in vitro and in vivo as surrogate conditions of IBD. Compared to the activity of 20 mM 5-aminosalicylate (5-ASA), an active metabolite of sulfasalazine (SSZ), showing 53% inhibition against TNF-α-induced U937-HT29 adhesion, fifteen 6-aminopyridin-3-ol derivatives at 1 μM concentration inhibited the adhesion over 50%. In the IC50 measurement, 5-ASA showed 18.1 mM, some selected 6-aminopyridin-3-ol derivatives showed IC50s ranging from 0.28 to 1.47 μM. The results indicate N-p-alkylphenyl analogues showed superior inhibition to 5-ASA against TNF-α-induced adhesion of monocytes to colon epithelial cells at three orders of magnitude lower concentration. Among the analogs, oral administration of four compounds showed potent alleviation of TNBS-induced rat colitis (67∼95% of colon weight recovery and 49∼82% of body weight recovery at 1 mg/kg dose) compared to SSZ (70% of colon weight recovery and 51% of body weight recovery at 300 mg/kg). As low as 1 mg/kg of the compounds showed comparable recovery activities to 300 mg/kg SSZ in those profiles, demonstrating its remarkable potency.
Conclusions: The in vitro and in vivo results strongly suggest that 6-amino-2,4,5-trimethylpyridin-3-ol can be an excellent anti-IBD scaffold.