NAFLD is characterized by abnormal lipid metabolism and excessive lipid accumulation in hepatocytes. Most of the herbs in JZD have been reported to take part in the regulation of lipid metabolism in NAFLD or other related diseases. Some researches showed that Alisma Orientale (AO) could prevent hepatic triglyceride accumulation through suppressing de novo lipogenesis and increasing lipid export, and control oxidative stress markers, lipoapoptosis, liver injury panels and inflammatory and fibrotic mediators, eventually influencing steatohepatitis and liver fibrosis [21, 22]. The components of Angelica Sinensis (AS) have been proved to regulate lipid and glucose metabolism [23–25]. Liu et al. found that a diet formula of Crataegus Pinnatifida (CP) and three other herbs could alleviate hepatic steatosis and insulin resistance in vivo and in vitro [26]. Yu et al. performed a serious of experiments to confirm that the active components of Polygonum Multiflorum (PM) could promote the lipolysis of cholesterol and triglyceride, increase the content of HTGL, and reduce LDL and VLDL [27–29]. However, the synergetic mechanisms of all the herbs in JZD were still unclear.
In our study, nuclear receptor transcription and lipid metabolism regulation were found as the core pathways which JZD mainly participated in when alleviating NAFLD. As we know, there are 48 nuclear receptors categorized into 7 subfamilies designated as NR0-NR6 [30]. Of particular importance in NAFLD are specific members of NR1 subfamily [31]. Most potential targets of JZD in Fig. 2 belong to NR1 subfamily, including PPARs (peroxisome proliferator-activated receptors, PPARA/PPARα, PPARD/PPARβ/δ, PPARG/PPARγ; NR1C1-3) and LXRα (liver X receptor α; NR1H3). PPARα activation induces the increase in fatty acid oxidation, ketogenesis and gluconeogenesis [32]. PPARβ/δ activation exerts regulatory effects on fatty acid catabolism, reverse cholesterol transport and energy metabolism, and even reduces insulin resistance and plasma glucose [33]. PPARγ shifts lipids from non-adipose organs such as the liver and skeletal muscles to white adipose tissue, leading to the attenuation of lipotoxicity [34]. In general, PPAR activation is thought to be beneficial in NAFLD, and clinical trials of single/dual receptor agonists are underway [31]. Another important nuclear receptor LXRα acts as the negative regulator of cholesterol metabolism through the induction of hepatocyte cholesterol catabolism, excretion, and the reverse cholesterol transport pathway [35]. Furthermore, HNF4A/HNF4α (hepatocyte nuclear factor 4α; NR2A1) also belongs to the subfamily of nuclear receptors. Previous study reported that HNF4α could prevent liver steatosis by controlling hepatic carboxylesterase 2 expression and modulating lipolysis, lipogenesis and endoplasmic reticulum in NAFLD [36]. Therefore, they are all potential therapeutic targets for the treatment of NAFLD.
Our research found that some ingredients in JZD might be the key ones for NAFLD treatment, such as emodin, hyperin and rhein. Many previous studies have reported that those ingredients could take part in the regulation of nuclear receptor. Emodin has been proved to increase the mRNA level of PPARγ and play a protective role in alcohol-mediated liver steatosis [37]. According to the activation of PPARγ signaling pathway, emodin could also alleviate atherosclerosis followed by promoting cholesterol efflux [38], or play other roles though regulating inflammatory response [39, 40] and nitric oxide production [41]. Furthermore, emodin has also been reported to regulate the expression of LXRα in atherosclerosis [38] and melanogenesis [42]. Hyperin is one of the chief flavonoid components of Ericaceae, Guttifera, Leguminosae and Celastraceae, and could remarkably induce the expression of PPARγ and attenuate inflammation of acute liver injury [43]. In addition, some studies also reported that rhein could target PPARγ signaling pathway and play anti-inflammatory activity [44, 45]. Moreover, rhein has been confirmed to ameliorate NAFLD and obesity and recover metabolic disorders through directly binding to LXRα [46, 47]. Thus, those key ingredients in JZD might improve NAFLD via regulating the nuclear receptors.
In conclusion, the multicomponent and multitarget characteristics of the therapeutic effects of JZD against NAFLD were effectively elucidated through network pharmacology approach. Emodin, emodin anthrone, hyperin, questin, rhein were speculated as the key active ingredients of JZD, and nuclear receptor transcription and lipid metabolism regulation were found as the core molecular mechanisms by which JZD alleviated NAFLD (Fig. 6). Therefore, our study will provide the scientific evidences of the clinical efficacy of JZD against NAFLD.