Pharmacokinetic comparisons of two different combinations of Shaoyao-Gancao Decoction in rats: Competing mechanisms between paeoniflorin and glycyrrhetinic acid

Abstract

Ethnopharmacological relevance

Shaoyao-Gancao Decoction (SGD), a well-known traditional Chinese medicine prescription, is a combination of Radix Paeoniae Alba (Paeonia lactiflora Pall, root) and Glycyrrhizae uralensis (Glycyrrhiza uralensis Fisch., root and rhizome, honeyed) for spasmolysis and emergency pain relief. Paeoniflorin (PF) and glycyrrhetinic acid (GA) are two typical active components of SGD for pain relief.

Aim of the study

To study comparative pharmacokinetics of ten bioactive compounds in SGDs with two different combinations of RP and GU, and therefore to investigate the herb–herb interaction mechanisms of Shaoyao-Gancao Decoction for better spasmolysis and emergency pain relief in rats.

Materials and methods

Herbal IR macro-fingerprinting was implemented to provide the full chemical fingerprints of RP, GU and SGD decoctions and to investigate the variation rule of the full chemical profile of SGDs with various combinations of RP and GU. A specifically developed HPLC-MS/MS assay coupled with protein precipitation method was employed to determine the plasma concentrations of the ten analytes. Male Wistar rats were orally administered with SGD1 (RP:GU, 1:1 (w/w)) and SGD2 ((RP:GU, 4:1 (w/w)) equivalent to 9.5 g/kg body weight of GU.

Results

Full chemical fingerprints of RP, GU and SGDs with various combinations of RP and GU were provided in the form of IR macro-fingerprints. Except for liquiritin, there were statistically significant differences (p<0.05 or p<0.01) of these analytes between SGD1 and SGD2 in in vivo pharmacokinetic study. Compared with the results when oral administrated with SGD1, six glycosides (PF, albiflorin, oxypaeoniflorin, isoliquiritin, ononin, and glycyrrhizin) exhibited higher systematic exposure levels (AUC_0−t) and slower elimination rates (CL) whereas two glycones (GA and isoliquiritigenin) were the reverse when administrated with SGD2.

Conclusions

Increasing the amount of RP attenuated the inhibitory effect of GA via competing being consumed by intestinal bacteria (or β-glucosidase) to reduce the conversion amount of glycyrrhizin to GA and subsequently to afford significantly higher bioavailability and longer efficacy of PF, glycyrrhizin, albiflorin, oxypaeoniflorin, isoliquiritin, and ononin, leading to better spasmolysis and emergency pain relief.

Introduction

Modern medical practitioners are convinced of the idea that chronic illnesses, such as diabetes (Kahn et al., 2006), HIV (Barouch, 2008), and cancers (Stephens et al., 2009), are polygenic and have multiple pathological mechanisms. “A drug that hits a single mechanism, no matter how hard, might not work.” (Xu, 2011) Consequently, a resurgence of herbal medicine (HM) usage in the Western world is occurring in respect that the multiple components in HM offer a unique opportunity to synergistically attack multiple disease-causing targets and can enhance the therapeutic efficacy and reduce the adverse effects of major components through drug–drug interaction in vivo (Wang et al., 2008, Tian, 2011). Modern scientific studies in HM have shown encouraging outcomes, particularly for the treatment of depression by St. John′s Wort (Hippius, 1998), promyelocytic leukemia by Realgar-Indigo naturalis (Wang et al., 2008) and reducing chemotherapy-induced gastrointestinal toxicity by PHY906 (Lam et al., 2010). A promising alternative medicine, traditional Chinese medicine (TCM), has been drawn increasing attention of the World (Grayson, 2011).

As a well-known TCM prescription (TCMP), Shaoyao-Gancao Decoction (SGD, Shakuyaku-Kanzo-to in Japanese) has been frequently used in Asia to treat abdominal spasmodic pain accompanying acute gastroenteritis (Zhai, 2003), muscle cramps (Hinoshita et al., 2003), and dysmenorrheal (Tanaka, 2003). SGD, initially recorded in Treatise on Febrile Diseases, a classical work of TCM written by in 3rd century in Eastern Han dynasty, is composed of Radix Paeoniae Alba (Paeonia lactiflora Pall, root) and Glycyrrhiza uralensis (Glycyrrhiza uralensis Fisch., root and rhizome, honeyed) with an equal proportion.

Radix Paeoniae Alba (RP), a herb of the family Ranunculaceae and the “Emperor” herb in SGD, is used to treat menstrual disorder, relieve intermittent celiodynia and myotonia (Lam et al., 2010). Monoterpene glucosides, particularly paeoniflorin, albiflorin and oxypaeoniflorin, are considered the main bioactive compounds responsible for anti-inflammatory and anti-anaphylaxis (Yamahara et al., 1982), analgesic effect (Zhang et al., 2008), neuromuscular blocking (Dezaki et al., 1996) and the inhibition of DNA cleavage (Okubo et al., 2000).

Glycyrrhiza uralensis (GU), a herb of the family Leguminosae and the “Minister” herb in SGD, has been used for regulating gastrointestinal function (Chen et al., 2009, Lam et al., 2010), cytoprotective action (Kim et al., 2004), anti-cancer (Zhang et al., 2009a), and immunoloregulation (Lee et al., 2009), analgesic effect (Zhang et al., 2008, Zhang et al., 2009) and treating skin disorders (Olukoga and Donaldson, 2000). Most of its bioactivities are believed to be related to flavonoids (mainly liquiritin, liquiritigenin, isoliquiritin and isoliquiritigenin) and triterpenoid saponins (mainly glycyrrhizin and its aglycone glycyrrhetic acid) (Zhang and Ye, 2009).

In clinic practice, the amount of RP in SGD is often greater than or equal to that of GU (Zhong et al., 2005). In general, the synergetic actions of multiple compounds in TCMP are considered to be the key role of their therapeutic effects. Pharmacological studies have demonstrated that monoterpene glucosides, flavonoids and triterpenoid saponins are the major bioactive compounds to regulate gastrointestinal function (spasmolysis and analgesic effect) in SGD (Palombo, 2006, Zhang et al., 2009). Therefore, it is essential to reveal the variation rule of the pharmacokinetic profiles of SGD with different combinations, which will be beneficial to the cognition of potential in vivo herb–herb interactions and rational administration in clinic. To our knowledge, however, there is no published report on the comparative pharmacokinetics of monoterpene glucosides, flavonoids and triterpenoid saponins after administrating different combinations of SGD.

The present study attempts to reveal the pharmacokinetic profiles of albiflorin, oxypaeoniflorin, paeoniflorin, liquiritin, isoliquiritin, liquiritigenin, isoliquiritigenin, ononin, glycyrrhizin and glycyrrhetinic acid in rat after oral administration of two different combinations of SGD extracts by employing a specifically developed HPLC-MS/MS method for simultaneous determination of the ten components in rat plasma, and subsequently to investigate the mechanism of herb–herb interaction for understanding the recipe-potency relationship of SGD.