Inhibitory effects of genistein on cytokine expression in colonic epithelial cell line.

Proinflammatory cytokines play an important role in the pathophysiology of Inflammatory Bowel Disease (IBD). Immunomodulatory compounds can inhibit perpetuation of chronic inflammation and thus curb tissue injury. Many of the current immunosuppressive agents lack efficacy and appropriate safety profiles. Genistein is a natural isoflavone of soybean origin that demonstrates anti-tumor, anti-oxidant and immunosuppressive effects. Osteoporosis and cardiovascular diseases have been treated with genistein. Pharmacokinetic studies demonstrate minimum toxicity with genistein. Human colonic adenocarcinoma cell line HCT-8 was used to compare the effects of genistein and dexamethasone on cytokine expression. The expression of human Cox-2, sICAM, IFN-[gamma], IL-8, IL-1[alpha] and IL-1[beta] were assessed by ELISA and mRNA quantification in constitutive and TNF-[alpha] stimulated conditions. NF[kappa]B transcription factor activity was studied using Transfactor assay and immunohistochemistry. Effect of genistein and dexamethasone on I[kappa]B degradation was studied using Western-blot analysis. HCT-8 cell line exhibited increased protein and mRNA levels of Cox-2, sICAM, IFN-[gamma] and IL-8 either constitutively or after TNF-[alpha] stimulation. Genistein and dexamethasone inhibited significantly (P < 0.005) the constitutive and TNF-[alpha] stimulated mRNA expression and protein secretion of IL-8, Cox-2, sICAM and IFN-[gamma]. We found that TNF-[alpha] stimulated cells exhibited activation of NF-[kappa]Bp65, which was inhibited significantly (P < 0.005) by genistein and dexamethasone in HCT-8 nuclear extracts and by immunohistochemistry. Western-blot analysis demonstrated that genistein and dexamethasone inhibited TNF-[alpha] induced degradation of I[kappa]B[alpha]. Genistein is involved in the pathway leading to inhibition of NF-[kappa]B transcription and inhibition of mediation of inflammation. Our results demonstrated that genistein and dexamethasone have almost similar inhibitory effects on cytokine expression. Therefore, since genistein is a natural isoflavone with few known side effects, the results of our studies suggest genistein maybe an efficacious modality in the management of IBD. Human studies are currently being developed with genistein.

Somaja Louis, MS, and John J. O'Brien, MD. Division of Gastroenterology and Hepatology, Southern Illinois University, School of Medicine, Springfield, IL.