Inhibition of nuclear factor kappa B (NF-κB) by aminosalicylates: Structure activity relationships

NF-κB is a transcription factor which regulates expression of many genes important in immunity and inflammation. Aminosalicylates are central to inflammatory bowel disease therapy, but their mechanism of action is not known. We sought to determine if aminosalicylates inhibit NF-κB in intestinal epithelial cells. Caco-2 cells were transfected with an NF-κB luciferase reporter gene. After 30 minute pre-incubation with varying concentrations of 5-aminosalicylic acid (ASA), 4-ASA, N-acetyl 5-ASA, sulfasalazine (SSZ), or olsalazine, the cells were stimulated with IL-1 for 4 hours and luciferase activity was read in cell lysates. NF-κB inhibition: 5-ASA 4-ASA SSZ olsalazine IC₅₀ 9 mM 25 mM 2 mM 1 mM N-acetyl 5-ASA did not inhibit NF-κB activity. In other experiments, the effect of 5-ASA and SSZ on inhibitory kappa Bα (IκBα) degradation was determined by quantitative immunoblot analysis of Caco-2 lysates after drug treatment and IL-1 stimulation. SSZ, but not 5-ASA inhibited IκBα degradation. In conclusion, aminosalicylates inhibit intestinal epithelial cell NF-κB activity. Azo-bound aminosalicylates inhibit IκBα degradation and are more potent inhibitors of NF-κB than free aminosalicylates.