Heme oxygenase-1 mediates the anti-inflammatory effect of Curcumin within LPS-stimulated human monocytes.

Curcumin, a polyphenolic compound derived from plant, regulates heme oxygenase (HO-1) expression within certain cell types; however, the Curcumin-mediated signal transduction in the regulation of HO-1 expression within human monocytes/macrophages is unclear. Herein, we show that Curcumin dose dependently induced HO-1 expression and HO-1 activity through the activation of PKCalpha, PKCdelta/ERK1/2, p38alpha, and PI3-kinase. In addition, H2O2 release is essential for Curcumin-mediated ERK1/2 and p38 phosphorylation and HO-1 expression. Further, Curcumin inhibited LPS-induced IL-1 and IL-6 secretion and blockage of HO-1 expression/activity by HO-1 siRNA or HO-1 inhibitor, SnPP reversed the inhibitory effects of Curcumin on cytokines secretion. HO-1 over-expression produced the same inhibitory effects of Curcumin on IL-1 secretion. Collectively, our results suggest that Curcumin inhibits cytokines secretion within LPS-stimulated monocytes through a mechanism that involves the action of HO-1.