We investigated the molecular mechanism by which berberine reduces nitric oxide (NO) expression and high-mobility group box 1 (HMGB1) release in lipopolysaccharide (LPS)-induced macrophages. Berberine significantly inhibited the LPS-stimulated NO production and HMGB1 release in macrophages. In addition, berberine also induced heme oxygenase (HO)-1 in a dose-dependent manner, which was mediated through activation of p38 MAPK and NF-E2-related factor 2 (Nrf2) signaling cascade in macrophages. The inhibitory effect of berberine on LPS-stimulated NO and HMGB1 release was reversed by siRNA-Nrf2, SB203580 (p38 MAPK inhibitor) and zinc protoporphyrin (ZnPP; HO-1 inhibitor) within macrophages. Therefore, we conclude that berberine inhibits the proinflammatory response to LPS in macrophages by up-regulation of the HO-1 level, in which p38 MAPK and Nrf2 have an important role. These results suggest that berberine may be useful as a therapeutic agent for the treatment of inflammatory diseases. Crown Copyright (C) 2013 Published by Elsevier Inc. All rights reserved.