Curcumin inhibits mitogen stimulated lymphocyte proliferation, NF-kappa-B activation and IL-2 signaling

Abstract

Background: T cell mediated acute rejection of transplanted organ continues to be a significant problem in solid organ transplantation. We had shown that curcumin is a potent inhibitor of Cyclosporin A resistant T cell CD28 co-stimulation pathway. Here we report the inhibitory effects of curcumin on mitogen stimulated lymphocyte proliferation, IL-2 synthesis/ signaling and on NFκB (component of IL2 promoter gene) activation . Methods: Human lymphocytes were isolated from fresh human spleen (SP-L). Mitogens [final concentrations of 2 μg/ml of concanavalin A (Con A), 5 μg/ml of phytohemagglutinin (PHA) and 20 ng/ml of phorbol-12-myristate 13-acetate (PMA)] were added to the designated wells in 96 well plate with 0.2 million SP and cultured for 48 h and then assayed for IL-2 synthesis by ELISA and 3H-thymidine uptake. In another parallel experiment we added IL-2 (0.5 nM) to stimulate the cells to bypass curcumin’s inhibition of IL-2 synthesis as the sole reason for inhibition of proliferation. Electrophorectic magnetic shift assay (EMSA) was performed in PMA (20 ng/ml,1 h) stimulated cells with or without curcumin to assay NFκB activation. Results: Curcumin at 2.5 μg/ml inhibited Con A, PHA and PMA stimulated SP-L proliferation at 77%, 23% and 48% respectively over controls and curcumin at 5 μg/ml completely (nearly 100%) inhibited the mitogen stimulated proliferation. Curcumin inhibited IL-2 synthesis in Con A, PHA and PMA stimulated SP-L in a concentration dependent manner with an ED50 (concentration required for 50% inhibition) measured at 3.5 μg/ml. Exogenous IL-2 stimulated SP-L proliferation was also inhibited by curcumin in a concentration dependent manner with an ED50 of 2 μg/ml. EMSA assay indicated that PMA at 20 ng/ml stimulated NFκB activation 253% over control which was inhibited by 24%, 38% and 73% respectively with curcumin at final concentrations of 2.5, 5 and 10 μg/ml respectively. Conclusion: Curcumin has profound immunosuppressive effects mediated via inhibition of IL-2 synthesis, mitogen and IL-2 induced activation of human lymphocytes. This effect may be mediated via NFκB inhibition.