**1. Introduction**

Glycyrrhizin (GL), a triterpenoid glycoside isolated from the roots of licorice plant (*Glycyrrhiza glabra* L.), has been traditionally used for treating peptic ulcer, hepatitis, and pulmonary bron‐ chitis. Various pharmacological effects of GL are well known, such as anti‐inflammatory [1, 2], anti‐allergic [3], and hepatoprotective activity [4–6]. In Japan, Stronger Neo‐Minophagen C, the active ingredient of which is GL, has been used as a treatment for over 25 years for patients with chronic hepatitis. Intravenous administration of GL decreases serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels in patients with chronic

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

hepatitis [7, 8]. The well‐defined model of hepatic injury induced by the injection of lipopoly‐ saccharide (LPS)/d‐galactosamine (GalN) has been widely used in studies of the mechanisms of human hepatitis. GalN is an aminosugar selectively metabolized by hepatocytes, which induces a depletion of the uridine triphosphate pool and thereby an inhibition of macromol‐ ecule (RNA, protein, and glycogen) synthesis in the liver [9]. Combination of LPS and GalN causes specifically hepatic failure in rodent [10]. Under the stimulation by LPS, liver macro‐ phages secrete various pro‐inflammatory cytokines including tumor necrosis factor (TNF)‐α which is a terminal mediator for apoptosis, subsequently leading to hepatic necrosis [11–14]. The hepatic lesion in this model resembles that of human hepatitis since the up‐regulation of TNF‐α level and hepatic apoptosis have been reported as pathogenic symptoms in human hepatitis. GL, an aqueous extract of licorice root, has been used for the treatment of chronic hepatitis to reduce the liver inflammation [15–17], but its effects on acute hepatic injury have been unclear. A recent report showed that Y‐40138, a synthetic compound, inhibits liver injury evoked by LPS/GalN through the suppression of TNF‐α and monocyte chemoattractant pro‐ tein‐1 and the augmentation of IL‐10 [18]. GL prevents anti‐Fas antibody‐induced mouse liver injury but has no effect on the upregulation of TNF‐α mRNA expression in the liver [6]. In our previous study [19], we reported that levels of serum of cytokines such as TNF‐α, interleukin (IL)‐6, IL‐10, IL‐12, and IL‐18 as well as those of serum ALT significantly increased after administration of LPS/GalN. GL had no effect on the production of TNF‐α, IL‐6, IL‐10, and IL‐12, whereas it significantly inhibited the increase in ALT levels and IL‐18 production. We have so far indicated that the inhibitory effect of GL is different from that of inhibitor for TNF‐α production, such as Y‐40138 [18] and bicyclol, a new synthetic anti‐hepatitis drug [20].

High‐mobility group proteins (HMGBs) possess a unique DNA‐binding domain that is subject to transcriptional regulation [21]. One of these proteins, HMGB1 (amphoterin), can be secreted into the extracellular milieu as a late‐acting mediator of LPS‐induced or sepsis‐induced lethality in mice [22]. Although HMGB1 is a non‐histone nuclear protein, it is passively released from necrotic cells [23] or actively secreted from stress‐received cells such as monocytes/macrophages as an inflammatory cytokine in response to endotoxin, tumor necrosis factor (TNF)‐α, or inter‐ leukin (IL)‐1β [22, 24–26]. HMGB1, which was released into the intravascular area, has great potential as a local inflammatory activator through intensifying the release of cytokines and che‐ mokines from stimulated cells [27] and interact with endothelial cells by up‐regulating surface receptors and causing the secretion of soluble pro‐inflammatory mediators [28]. Extracellular HMGB1 works properly as a damage‐associated molecular patterns (DAMPs) molecule and increases powers of pro‐inflammatory signaling paths by activating pattern recognition recep‐ tors (PRRs) including toll‐like receptor 4 (TLR4) and/or the receptor for advanced glycation end‐ products (RAGE) [25, 29]. Increasing evidence suggests that HMGB1 may also operate so as to assist the progress of the recognition of other immune co‐activators such as LPS, DNA, and IL‐1 by being excessively desirous of the binding to these molecules [30–32]. However, the mecha‐ nisms by which GL inhibits inflammation induced with pathogen‐associated molecular patterns (PAMPs) such as LPS or endogenous DAMPs such as HMGB1 have not been clearly revealed.

Previous results have suggested that glycyrrhizin (GL) and glycyrrhetinic acid (GA) exert their protective effects by the membrane stabilization which results in inhibiting the prolongation of oxidative stress [33]. Furthermore, progesterone‐receptor membrane component 1 (PGRMC1) was proposed as a new target protein for GL. PGRMC1 is a haem‐containing protein that inter‐

acts with epidermal growth factor (FGFR) and cytochrome P450 to regulate cancer prolifera‐ tion and chemoresistance [34]. GL is thought to reduce cancer proliferation via PGRMC1. On the other hand, a research work utilizing nuclear magnetic resonance (NMR) and fluorescence methods revealed the supplementary mechanism by which GL directly binds to HMGB1 and suppresses the HMGB1 chemoattractant and mitogenic activities [35]. Recent studies, further‐ more, have reported that GL reduces inflammatory infiltrates by inhibiting the cellular prolifer‐ ation and migration, and formation of blood vessels induced by HMGB1 [36]. In this chapter, we evaluated the underlying new mechanism supporting various pharmacological effects of GL on the basis of upcoming data of our experiment on hepatitis induced by an injection of LPS/GalN.
