Effect of 18β-glycyrrhetinic acid and hydroxypropyl γcyclodextrin complex on indomethacin-induced small intestinal injury in mice

Abstract

Non-steroidal anti-inflammatory drugs (NSAIDs)-induced small intestinal injury is a serious clinical event with recent advances of diagnostic technologies, but a successful therapeutic method to treat such injuries is still lacking. Licorice, a traditional herbal medicine, and its derivatives have been widely used for the treatment of a variety of diseases due to their extensive biological actions. However, it is unknown whether these derivatives have an effect on NSAIDs-induced small intestinal damage. Previously, the anti-inflammatory effects of three compounds extracted from the licorice root, glycyrrhizin, 18β-glycyrrhetinic acid, and dipotassium glycyrrhizinate, were compared in vitro cell culture. The most prominent inhibitory effect on the tumor necrosis factor-α (TNF-α) production was observed with the administration of 18β-glycyrrhetinic acid as an active metabolite of glycyrrhizin. In this study, a complex compound of 18β-glycyrrhetinic acid and hydroxypropyl γcyclodextrin was examined to improve the oral bioavailability. After administration of this complex to indomethacin treated mice, a significantly high plasma concentration of 18β-glycyrrhetinic acid was detected using the tandem mass spectrometry coupled with the HPLC. Furthermore, the complex form of 18β-glycyrrhetinic acid and hydroxypropyl γcyclodextrin reduced mRNA expressions of TNF-α, interleukin (IL)-1β, and IL-6, which was histologically confirmed in the improvement of indomethacin-induced small intestinal damage. These results suggest that the complex of 18β-glycyrrhetinic acid and hydroxypropyl γcyclodextrin has the potential therapeutic value for preventing the adverse effects of indomethacin-induced small intestinal injury.

Introduction

Non-steroidal anti-inflammatory drugs (NSAIDs), such as an indomethacin, have been recognized to damage the gastrointestinal tract as a serious adverse event (Allison et al., 1992). Recent advances in diagnostic methods have enabled visualization of the entire small intestine (Maiden et al., 2005), and studies using these techniques have shown that mucosal breaks of the small intestine is high prevalence in patients receiving NSAIDs (Maiden et al., 2005, Graham et al., 2005). The clinical importance of NSAIDs-induced small intestinal injury has been extended, but suitable therapeutic agents have not been developed. Recently, several endogenous and exogenous factors have been determined to have an effect on NSAIDs-induced small intestinal injury using in vitro cell culture and in vivo experiments (Higuchi et al., 2009, Yasuda et al., 2011, Kawahara et al., 2011, Ikawa et al., 2012). However, the mechanism of NSAIDs-induced small intestinal injury is rather complicated (Higuchi et al., 2009), and a suitable therapeutic strategy has not yet been fully established.

Herbal medicines derived from the plant extracts are widely employed in the treatment of clinical diseases, but there is relatively little knowledge about their exact action. Licorice, the root of Glycyrrhiza glabra, an important herbal medicine, has been effectively used for its medical potential. Glycyrrhizin (Fig. 1A), a major water-soluble constituent of licorice root, is a triterpene glycoside that possesses one molecule of 18β-glycyrrhetinic acid (18β-GA, Fig. 1B) and two molecules of glucuronic acid. After oral administration, glycyrrhizin is hydrolyzed by glucuronidase of intestinal bacteria to its principal aglycone 18β-GA, which is absorbed into the blood stream (Takeda et al., 1996). Dipotassium glycyrrhizinate (Fig. 1C) is another related soluble compound extracted from the licorice root (Trotta et al., 2002). These compounds extracted from licorice root have been shown to have several beneficial pharmacological activities. Briefly, glycyrrhizin is known to have anti-inflammatory (Ohuchi et al., 1981), anti-ulcerative effects (Doll and Hill, 1962), and steroid-like action (Kumagai et al., 1957). Glycyrrhizin and 18β-GA have been shown to protect against a number of hepatotoxins (Nose et al., 1994). A recent study indicated that 18β-GA can delay the development of auto-immune disease (Horigome et al., 2001). In addition, dipotassium glycyrrhizinate has been applied for topical use in the field of dermatology (Trotta et al., 2002). Despite broad pharmacological roles as anti-inflammatory agents, there are few data on the comparative effects of compounds extracted from licorice root.

Cyclodextrins (CDs) are cyclic α-1,4-glucans composed of six to more than 100 glucose units (Loftsson et al., 2007). CDs are produced from starch or starch derivates using cyclodextrin glycosyltransterase. The enzymatic product is usually a mixture of CDs, including mainly α, β, and γCD that consist of six, seven, or eight glucose units, respectively, (Loftsson et al., 2007). Compared with α and βCDs, γCD exhibits more favorable properties in terms of the size of its internal cavity, water solubility, and bioavailability (Li et al., 2007). In addition, hydroxypropyl γCD (HP-γCD, Fig. 1D) is prepared by substituting hydroxypropyl groups on the natural form of γCD (Loftsson et al., 2007). In contrast to the normal γCD, HP-γCD has higher water solubility and has a slightly more benign toxicological profile (Bai et al., 2010). However, there have been few reports on the encapsulation properties of HP-γCD.

More recently, we have compared the anti-inflammatory effect of three compounds extracted from licorice root on mouse macrophages (Ishida et al., 2012), and 18β-GA of an active metabolite of glycyrrhizin has been identified as a promising anti-inflammatory candidate. In this study, we assessed the possible role of HP-γCD as a clathrate compound to improve oral bioavailability of 18β-GA. We further examined the anti-inflammatory effect of complex of 18β-GA and HP-γCD in an indomethacin-induced small intestinal injury in mice.