Wogonin Inhibits Osteoclast Formation Induced by Lipopolysaccharide Sungil Jang 1,2† , Eun Jung Bak 1† , Minyoung Kim 1,2 , Jin Moon Kim 1,2 , Won-Yoon Chung 1,2 , Jeong-Heon Cha 1,2 , Yun-Jung Yoo 1,2 * 1 Department of Oral Biology, BK21 Project, Oral Science Research Center, and Research Center for Orofacial Hard Tissue Regeneration, Yonsei University College of Dentistry, Seoul, Korea 2 Department of Applied Life Science, The Graduate School, Yonsei University, Seoul, Korea To evaluate the inhibitory activity of wogonin against lipopolysaccharide (LPS)-induced bone resorption, we investigated the effect of wogonin on osteoclastogenesis induced by LPS. Wogonin inhibited LPS-induced osteoclastogenesis in co-cultures of mouse calvaria-derived osteoblasts and bone marrow-derived pre- osteoclasts. Wogonin also suppressed osteoclastogenesis in LPS-injected mouse calvaria. In osteoblasts, the upregulation of receptor activator of nuclear factor-κB (RANKL) expression and the downregulation of osteo- protegerin (OPG) expression by LPS were inhibited by wogonin. Wogonin and NS-398, a COX-2 inhibitor, suppressed LPS-stimulated PGE 2 production in osteoblasts. NS-398 inhibited the effect of LPS on RANKL and OPG expression in osteoblasts. These results suggest that wogonin acts as an inhibitor of LPS-induced osteoclastogenesis through downregulation of RANKL and upregulation of OPG expression via blockage of PGE 2 production. Based on these results, wogonin has potential for use as a therapeutic agent in bacteria- induced bone resorption. Copyright © 2009 John Wiley & Sons, Ltd. Keywords: wogonin; osteoclastogenesis; lipopolysaccharide. INTRODUCTION Osteoclasts are tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells with bone- resorbing activity and are differentiated from hemato- poietic cells through multiple steps including proliferation, expression of TRAP, and fusion of cells (Takahashi et al., 1999; Boyle et al., 2003). Osteo- blasts regulate osteoclast differentiation by expression of osteoclastogenesis-inducing or -inhibiting factors (Takahashi et al., 1999; Hofbauer et al., 2000). Receptor activator of nuclear factor-κB ligand (RANKL) is an essential osteoclastogenesis-inducing factor that is expressed as a membrane-bound and a secreted protein by osteoblasts (Takahashi et al., 1999; Hofbauer et al., 2000; Boyle et al., 2003). Osteoclast precursors recognize RANKL through RANK, a receptor of RANKL, and then differentiate into osteoclasts in the presence of M-CSF (Takahashi et al., 1999; Hofbauer et al., 2000; Suda et al., 2004). Osteoprotegerin (OPG) is an osteoclastogenesis-inhibiting factor that inhibits osteoclastogenesis by blocking the RANKL-RANK interaction (Takahashi et al., 1999; Hofbauer et al., 2000). Therefore, the expression level of RANKL and OPG in osteoblasts is an important factor that can be used to determine whether osteoclast differentiation is inducible or not (Hofbauer et al., 2000; Boyce and Xing, 2007). Periodontitis is an inflammatory disease caused by bacteria that is characterized by the resorption of alve- olar bone, which surrounds the root of tooth (Jeffcoat, 1993). Representative pathogens that induce periodon- titis are gram-negative bacteria (Socransky and Haffajee, 2005). Lipopolysaccharide (LPS) is a compo- nent of the cell wall of gram negative bacteria that stimulate osteoclast differentiation (Nair et al., 1996; Suda et al., 2004; Choi et al., 2007). Therefore, it has been suggested that LPS stimulates bone resorption in periodontitis. As a result, LPS is commonly used as an inducer of periodontits in animal models (Rogers et al., 2007a; 2007b). Wogonin (5, 7-dihydroxy-8-methoxyflavone) is a fla- vonoid extracted from the root of Scutellaria baicalensis Gerogi that has long been used in traditional medicine in east Asian countries (Tai et al., 2005). Previous studies have revealed that wogonin displays anti-inflammatory, anticancer, antiviral, and neuroprotective effects (Tai et al., 2005). Furthermore, it is known that the anti- inflammatory effects of wogonin on macrophage occur via inhibiting the activity and induction of COX-2, an inducer of PGE 2 (Wakabayashi and Yasui, 2000; Chen et al., 2001; Chi et al., 2001). Additionally, PGE 2 was reported to mediate LPS-induced osteoclast formation in vitro and in vivo (Sakuma et al., 2000; Suda et al., 2004). Taken together, these reports indicate the pos- sibility that wogonin may inhibit LPS-induced osteo- clastogenesis via the inhibition of PGE 2 production. Therefore, in this study, we investigated the effect of wogonin on LPS-induced osteoclast formation using in vitro and in vivo systems. * Correspondence to: Yun-Jung Yoo, DDS, PhD, Department of Oral Biology, Yonsei University College of Dentistry, 134 Sinchon-dong, Seodaemoon-gu, Seoul, 120-752, Korea. E-mail yu618@yuhs.ac † Sungil Jang and Eun Jung Bak contributed equally to this work. Received 17 June 2009 Copyright © 2009 John Wiley & Sons, Ltd. Accepted 13 August 2009 PHYTOTHERAPY RESEARCH Phytother. Res. 24: 964–968 (2010) Published online 8 December 2009 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/ptr.3013