Bioactive constituents and action mechanism of Xiaoyao San for treatment of non-alcoholic fatty liver disease

Abstract

Xiaoyao San (XYS) is a classic Chinese medicine prescription. It is traditionally used to relieve syndrome of “liver stagnation and spleen deficiency”, a common syndrome type in traditional Chinese medicine, through soothing liver, tonifying spleen, and nourishing blood. Correspondingly, XYS has long application in the treatment of depression, dyspepsia and liver diseases. Given the rising of cutting-edge researches on XYS, there’s a significant need to diligently uncover the bioactive constituents and action mechanisms of XYS for treating non-alcoholic fatty liver disease accordingly.

Key Words: Xiaoyao San; Bioactive constituents; Mechanisms; Non-alcoholic fatty liver disease; Fibrosis

Core Tip: Xiaoyao San (XYS) is a classic Chinese medicine prescription. It consists of 8 kinds of herbs, which thus contains abundant bioactive constituents to exert various biological effects. XYS has functions on relief of “liver stagnation and spleen deficiency”, and has long been used to treat liver diseases. Extensive effort has been made in the investigation of effective substances and action mechanisms of XYS against non-alcoholic fatty liver disease, and these achievements could contribute to build up the scientific foundation for its clinical application.

TO THE EDITOR

We have read the interesting study of Mei et al[1], in which they investigated the efficacy and mechanisms of Xiaoyao San (XYS) in alleviating hepatic injury, steatosis and inflammation. This study intriguingly revealed that XYS significantly decreased hepatic steatosis and inflammatory response in a choline-deficient/high-fat diet-induced rat nonalcoholic steatohepatitis (NASH) model. Metabolomics analysis indicated that XYS altered the overall metabolite profile in NASH model, and steroid hormone synthesis was one of the main target pathways affected by XYS. In addition, XYS increased Adenosine monophosphate-activated protein kinase α phosphorylation, and decreased peroxisome proliferator activated receptor-γ, cyclooxygenase 2 and fatty acid synthase expression, which are significant regulators of lipid metabolism and inflammation. Add to the increased phosphatase and tensin homolog expression induced by XYS, finally the mechanism was attributed to inhibit the metabolism of male hormones to suppress liver steatosis and inflammation.

The design and content of the study carried out by Mei et al[1] are clear and comprehensive, and the findings seem to advance the field of XYS research and application in a meaningful way. However, this study does possess certain limitations. For instance, the absence of quality control of XYS makes no way to know the effective substances accounting for these effects. As a classic Chinese medicine prescription, XYS has long application in the treatment of depression, dyspepsia and liver diseases[1-3]. It consists of 8 kinds of herbs: Radix bupleuri, radix angelicae sinensis, radix paeoniae alba, rhizoma atractylodis macrocephalae, poria, herba menthae, rhizoma zingiberis recens and radix glycyrrhizae. Each herb contains various constituents, and thus the formula XYS contains a greater diversity of constituents. To date, the phytochemical constituents in XYS have been qualitatively and quantitatively analyzed by different methods[4-7]. The representative bioactive constituents include volatile oils (i.e., liguistilide from radix angelicae sinensis, menthol from herba menthae, zingiberol from rhizoma zingiberis recens), saikosaponins (i.e., saikosaponin a from radix bupleuri), glucosides of paeonia (i.e., paeoniflorin from radix paeoniae alba), flavone glycosides (i.e., liquiritin from radix glycyrrhizae), and atractylenolides (i.e., atractylenolide-1 from rhizoma atractylodis macrocephalae). These constituents could regulate multiple targets to exert miscellaneous biological functions, and their interactions eventually generate the pharmacological effects on non-alcoholic fatty liver disease (NAFLD).

Additionally, the wide diversity of constituents in XYS makes it difficult to study the action mechanism of XYS in vivo. Indeed, the aforementioned article failed to clarify the causal relationship between symptom relief and suppressed male hormone metabolism after XYS treatment. In this case, it is not rigor to conclude the therapeutic mechanism of XYS to modulating the male hormone metabolic pathway. By contrast, a recent study revealed that XYS has an estrogen-like effect to inhibit hepatic steatosis in a high-fat diet-induced mouse model[8]. XYS significantly increased the estrogen receptor α (ERα) expression, inhibited lipogenic genes transcription, and these effects were partly reversed by the antiestrogen fulvestrant. Thus, the therapeutic mechanism of XYS was attributed to reducing the expression of genes related to lipogenesis through ERα pathway. Noticeably, the two studies adopted different animal models, especially Mei et al[1] established NAFLD model in male SD rats[1], while Hu et al[8] did it in female apolipoprotein E-/- mice[8]. This gender difference might affect the regulatory effects of XYS on the hormone metabolism, and result in the varied results of mechanism investigation. Nevertheless, the androgen-inhibition effect of XYS in male animal model could be matchable to its estrogen-like effect in female animal model. To sum up, these studies suggested that XYS could alleviate NAFLD through regulating hormone metabolism to inhibit hepatic lipid accumulation and inflammatory response.

As a spectrum of liver disease, NAFLD covers a range from non-alcoholic fatty liver to NASH, and related fibrosis/cirrhosis. Recently, several studies have evaluated XYS in the treatment of liver fibrosis/cirrhosis[9-12]. Yang et al[9] found that XYS ameliorated inflammation and fibrosis in mice with restraint stress-induced NASH[9]. In this work, XYS was regarded as an advantageous farnesoid X receptor (FXR) activator, and its efficacy could be derived from regulating the FXR/nucleotide-binding domain, leucine-rich repeat, and pyrin domain-containing protein 3 signaling pathway[9]. Moreover, the anti-fibrosis effects of XYS were also investigated in carbon tetrachloride induced liver fibrosis rat model[10,11]. XYS showed an anti-liver fibrotic effect as indicated by reduced histopathological changes of liver fibrosis, hydroxyproline content and levels of alpha-smooth muscle actin and collagen I[10]. Network pharmacology and transcriptomics analysis demonstrated its anti-liver fibrotic activity could occur via inhibiting janus kinase (JAK)-signal transducer and activator of the transcription and phosphatidylinositol-3-kinase protein kinase B (Akt)-forkhead box transcription factors class O (FoxO) signalling[10]. Likewise, the study of Zhou et al[11] found that XYS markedly alleviated liver fibrosis and action mechanism might be involved in the regulation of transforming growth factor beta 1/Smad and Akt/FoxO signaling pathways[11]. Although the anti-cirrhosis effect of XYS has not yet been evaluated in animal model, its efficacy and mechanism were deduced based on dynamic network biomarker algorithm, network pharmacology and transcriptomic data in the study of Lu et al[12]. Their findings suggested that XYS might be effective against cirrhosis and CCAAT/enhancer binding protein alpha, interleukin 7 receptor, epidermal growth factor receptor, and colony stimulating factor 1 might be the potential therapeutic targets.

In conclusion, XYS is a classic Chinese medicine prescription which has functions against “liver stagnation and spleen deficiency”. Recently, extensive effort has been made in the investigation of its therapeutic substances and mechanisms for NAFLD, and these achievements could contribute to build up the scientific foundation for its clinical application.