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Analytical Cellular Pathology
Volume 2018, Article ID 8047610, 8 pages
Review Article

Role of Muramyl Dipeptide in Lipopolysaccharide-Mediated Biological Activity and Osteoclast Activity

Division of Orthodontics and Dentofacial Orthopedics, Department of Translational Medicine, Tohoku University Graduate School of Dentistry, 4-1 Seiryo-machi, Aoba-ku, Sendai 980-8575, Japan

Correspondence should be addressed to Hideki Kitaura;

Received 28 September 2017; Accepted 10 January 2018; Published 14 February 2018

Academic Editor: Jonathan S. Reichner

Copyright © 2018 Hideki Kitaura et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Lipopolysaccharide (LPS) is an endotoxin and bacterial cell wall component that is capable of inducing inflammation and immunological activity. Muramyl dipeptide (MDP), the minimal essential structural unit responsible for the immunological activity of peptidoglycans, is another inflammation-inducing molecule that is ubiquitously expressed by bacteria. Several studies have shown that inflammation-related biological activities were synergistically induced by interactions between LPS and MDP. MDP synergistically enhances production of proinflammatory cytokines that are induced by LPS exposure. Injection of MDP induces lethal shock in mice challenged with LPS. LPS also induces osteoclast formation and pathological bone resorption; MDP enhances LPS induction of both processes. Furthermore, MDP enhances the LPS-induced receptor activator of NF-κB ligand (RANKL) expression and toll-like receptor 4 (TLR4) expression both in vivo and in vitro. Additionally, MDP enhances LPS-induced mitogen-activated protein kinase (MAPK) signaling in stromal cells. Taken together, these findings suggest that MDP plays an important role in LPS-induced biological activities. This review discusses the role of MDP in LPS-mediated biological activities, primarily in relation to osteoclastogenesis.