Chinese Herbal Medicine for Wilson's Disease: A Systematic Review and Meta-Analysis

Wilson's disease (WD) is a rare autosomal recessive inherited disorder of chronic copper toxicosis. Currently, Chinese herbal medicines (CHM) is widely used for WD. Here, we conducted an updated systematic review to investigate the efficacy and safety of CHM for WD and its possible mechanisms. Randomized-controlled clinical trials (RCTs), which compared CHM with Western conventional medicine or placebo for WD, were searched in six databases from inception to July 2017. The methodological quality was assessed using 7-item criteria from the Cochrane's collaboration tool. All the data were analyzed using Rev-Man 5.3 software. Eighteen studies involving 1,220 patients were identified for the final analyses. A score of study quality ranged from 2/7 to 4/7 points. Meta-analyses showed that CHM could significantly increase 24-h urinary copper excretion and improve liver function and the total clinical efficacy rate for WD compared with control (p < 0.05). Additionally, CHM was well tolerated in patients with WD. The underlying mechanisms of CHM for WD are associated with reversing the ATP7B mutants, exerting anti-oxidation, anti-inflammation, and anti-hepatic fibrosis effects. In conclusion, despite the apparent positive results, the present evidence supports, to a limited extent because of the methodological flaws and CHM heterogeneity, that CHM paratherapy can be used for patients with WD but could not be recommended as monotherapy in WD. Further rigorous RCTs focusing on individual CHM formula for WD are warranted.


INTRODUCTION
Wilson's disease (WD) is a rare autosomal recessive inherited disorder that causes copper poisoning in the body, predominantly in the liver and the brain (Walshe, 2009). The global prevalence of WD is between 1 in 5,000 and 1 in 30,000 (Gomes and Dedoussis, 2015). Epidemiological studies have shown a higher incidence and prevalence of WD in China than in western countries (Hu et al., 2011). The WD gene was identified as the trans-membrane copper transporter ATP7B in hepatocytes (Bull et al., 1993;Petrukhin et al., 1993). An absent or reduced function of ATP7B protein causes decreased hepatocellular excretion of copper into bile. In WD, the ever-increasing positive copper balance overwhelms the copper chaperones (copper-binding proteins), causing elevated levels of free copper and copper-induced tissue injury (Patil et al., 2013). Copper metabolism disorder results in multifaceted neurological, hepatic and psychiatric symptoms (Brewer, 2009). When left untreated, WD is fatal. With early diagnosis and appropriate treatment, patients can obtain excellent prognosis (Roberts and Schilsky, 2008;Coffey et al., 2013). Currently, medical treatments and liver transplantation are two main therapeutic approaches that can achieve the generation of a negative copper balance (Hedera, 2017). The EASL Clinical Practice Guidelines of Wilson's disease by European Association for Study of Liver recommended D-penicillamine, trientine, zinc, tetrathiomolybdate, and dimercaprol as medications. However, many side effects such as nephrotoxicity, dermatological toxicity, bone marrow toxicity, severe thrombocytopenia, and total aplasia have been observed in patients with lifelong pharmacological therapy (European Association for Study of Liver, 2012). Liver transplantation is an effective treatment for patients of WD with acute liver failure but it is used only in particular scenarios because of the risks including relatively low engrafting efficiency and lifelong immunosuppression (Filippi and Dhawan, 2014). Thus, an alternative and/or complementary strategy for WD is increasingly sought.
Chinese herbal medicine (CHM) is widely used for WD in the clinic (Ren et al., 1997;Han et al., 1999Han et al., , 2014Hong et al., 2000;Cui and Zhao, 2001;Xiao, 2003;Xue et al., 2007;Zhang, 2007;Wang, 2008, 2010;Wang et al., 2010;Xu et al., 2012a,b;Hu, 2014;Zhang et al., 2014a,b;Fang, 2015;Jiang, 2016;Li et al., 2016), and has been extensively tested by experimental research (Zhang et al., 2011;Lin et al., 2015). Pharmacological studies have shown that CHM can improve the urinary copper excretion and hepatic fibrosis, and protect the brain, liver and kidney (Lutsenko et al., 2007). These beneficial effects are associated with ATP7B gene reversing, anti-oxidant functions, anti-inflammatory actions and suppression of apoptosis (Rosencrantz and Schilsky, 2011). Our group has demonstrated that CHM brings benefits to some patients with WD (Wang et al., 2012). In addition, emerging randomized-controlled clinical trials (RCTs) continuously report the effectiveness and safety of CHM for WD. Therefore, in the present study we aimed to conduct an updated systematic review of CHM for WD focusing on the clinical evidence and possible mechanisms.

Database and Search Strategies
Two trained researchers systematically searched the following databases from their inception to July 2017: PubMed, Cochrane Central Register of Controlled Trials, Chinese National Knowledge Infrastructure, Chinese VIP information and WanFang database. The search strategy of PubMed was as follows, and it was modified to suit other English or Chinese databases. PubMed

Types of Studies
Only RCTs were included, irrespective of population characteristics, blinding, publication status, and language. Quasi-RCTs, such as those in which patients were allocated according to date of birth and order of admission number, were excluded.

Types of Participants
We included participants with a diagnosis of WD, according to Chinese Yang Renmin criteria (1995) (Yang, 1995), Chinese Medical Association of Neurology Guidelines for the diagnosis and treatment of hepatolenticular degeneration (2008)  Studies comparing one kind of CHM therapy to another CHM were excluded.

Types of Outcome Measures
The primary outcome measures were: (1) the amount of copper excreted in the urine in a 24 h period, liver function, and the indicator of hepatic fibrosis; (2) clinical deficit score: the Unified Wilson's Disease Rating Scale (Leinweber et al., 2008) or the Novel Global Assessment Scale (GAS) for Wilson's Disease (Aggarwal et al., 2009); (3) imaging: Brain MRI and functional neuroimaging. The secondary outcome measures were: the total clinical effective rate, laboratory values and adverse events.

Selection and Data Extraction
The data were extracted using a standardized data extraction form, including study design, eligibility criteria, characteristics of the sample, the course of treatment, interventions, outcomes, the constituent of CHM and pharmaceutical quality control. Reasons Frontiers in Pharmacology | www.frontiersin.org for the exclusion of studies were recorded. Any disagreements were resolved by discussion with or by involving a third author.

Assessment of Risk of Bias
The RoB of included articles was assessed using the 7-item criteria from the Cochrane' s collaboration tool (Higgins et al., 2011). Two authors independently evaluated the study quality, and the final result was identified by discussion when countering the disagreement.

CHM Composition
The frequency of use of the particular herb was calculated and those used at a high frequency were described in detail.

The Reporting Completeness of the Clinical Studies
In order to assess the reporting completeness with a rating system quality of the clinical studies, we used a rating system according to our previous articles (Wang et al., 2019) as follows: (1) high quality: full information about the botanical material is provided, including a voucher specimen; (2) moderate quality: only partial information about the botanical material is provided and a voucher specimen is missing; there are taxonomic inaccuracies; (3) low quality: inadequate information and overall taxonomically is inadequate.

Statistical Analysis
The pooled analyses were carried out with RevMan 5.3 software. Heterogeneity was assessed using the Cochrane Q-statistic test (p < 0.05 was considered statistically significant) and the I 2statistic test. A fixed effects model (I 2 < 50%) or a random effects model (I 2 > 50%) was used depending on the value of I 2 . Funnel plots were used to visually estimate publication bias. We calculated the standard mean difference (SMD) with 95% Confidence Intervals (CIs). Sensitivity analyses omitting everyone, which study at a time from the original analysis were conducted to demonstrate our main results to be robust.

Description of Studies
We identified 1,049 hints, of which 364 articles remained after removal of duplicates. Through screening titles and abstracts, 320 studies were excluded because they were case reports, they lacked a comparison group, they were not CHM studies or reports of clinical trials. After full-text evaluation of the remaining 44 articles, 26 studies were excluded for the following reasons: (1) 7 articles were not RCTs; (2) 3 articles included CHM treatment in control groups; (3) 2 articles included oxiracetam or tiopronin in control group; (4) 6 articles have inappropriate outcome measures; (5) 8 articles were suspected of being published more than once. Eventually, 18 eligible studies were identified (Figure 1).

The Reporting Completeness of the Clinical Studies
We accessed the reporting completeness of the material in each study with a rating system, which is related to the information about the botanical material and voucher specimens. Only two studies (Han et al., 2014;Zhang et al., 2014a) are of high quality, which provided the full information about the botanical material and included voucher specimens. Twelve studies (Ren et al., 1997;Han et al., 1999;Hong et al., 2000;Cui and Zhao, 2001;Xiao, 2003;Xue et al., 2007;Zhang, 2007;Wang, 2008, 2010;Xu et al., 2012a;Hu, 2014;Zhang et al., 2014b) are of moderate quality, which provided partial information about the botanical material and did not provide voucher specimens. Four studies Xu et al., 2012b;Fang, 2015;Jiang, 2016) are of low quality with inadequate information and were overall taxonomically inadequate. The quality of each included clinical study is summarized in Table 3.

CHM vs. Placebo
None of RCTs used a specific comparison between CHM and placebo.

CHM Plus WCM vs. WCM 24 h excretion of urinary copper
Nine studies were included. Meta-analysis of 5 studies (Xu et al., 2012a,b;Hu, 2014;Zhang et al., 2014b;Fang, 2015) reported a significant effect of CHM on increasing the amount of 24 h excretion of urinary copper in patients with WD compared to the control (n = 228, SMD 0.93, 95% CI [0.65 to 1.21], p < 0.01;heterogeneity: χ 2 = 4.01, df = 4 (p = 0.40); I 2 = 0%) (Figure 3). Four studies (Ren et al., 1997;Hong et al., 2000;Cui and Zhao, 2001;Zhang, 2007) failed for pool analysis because the measurement unit of 24 h excretion of urinary copper was different from the remaining. However, they all got the significant effects of improving the 24 h excretion of urinary copper on patients (p < 0.05).

Liver function and the indicator of hepatic fibrosis
Two studies (Xue et al., 2007;Xu et al., 2012a) used the value of serum alanine aminotransferase (ALT) as the indicator of liver function. Pooled data showed that CHM was significantly better at decreasing the ALT compared with control group [n = 117, SMD−0.62, 95% CI [−1.00 to −0.24], p < 0.01; heterogeneity: χ 2 = 1.40, df = 1 (p = 0.24); I 2 = 29%], (Figure 4). One study (Xiao, 2003) used ALT recovery rate as the indicator of liver function, and it demonstrated significant effects on decreasing the ALT (p < 0.05). One study (Xiao, 2003) showed that CHM had significant effects on reducing HA, PCIII, and LN (p < 0.05), however, another study (Xue et al., 2007) showed that CHM had no effect on reducing HA, PCIII and LN in short time (p > 0.05).

The total clinical effective rate
Data on the rate of total clinical effectiveness were available from eight studies with 487 participants included. Meta-analysis of 8 studies showed a significant effect of CHM on increasing the total clinical effective rate compared with control group (n = 487, RR 1.27, 95% CI [1.15 to 1.39], p < 0.01; heterogeneity: χ 2 = 6.56, df = 7 (p = 0.48), I 2 = 0%) (Figure 5).

Laboratory values or imaging indices
One study (Xu et al., 2012b) showed that CHM paratherapy is significant for increasing portal venous flow (PVF) and splenic vein flow (SVF) (p < 0.05) compared with WCM, whereas another study (Zhang et al., 2014b) showed no difference. One

F, Full information about the botanical material is provided; P, Partial information about the botanical material is provided; I, Inadequate information about the botanical material is provided; +, includes a voucher specimen; -, a voucher specimen is missing.
study (Fang, 2015) showed that CHM could significantly improve the cardiac function according to electrocardiogram, ejection fraction, and myocardial enzyme spectrum relative to WCM (p < 0.05). One study (Han et al., 2014) showed that CHM is significant for improving the Mini-mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA) (p < 0.05) compared with WCM.

Adverse Events
Adverse effects were reported in 8 studies (Ren et al., 1997;Han et al., 1999;Wang, 2008, 2010;Xu et al., 2012a,b;Hu, 2014;Fang, 2015). There were no significant differences in routine blood, routine urine, routine stool, and osteoporosis after CHM treatment in three studies (Ren et al., 1997;Xu et al., 2012a,b). Five studies (Han et al., 1999;Wang, 2008, 2010;Hu, 2014;Fang, 2015) reported that CHM could significantly reduce the adverse events of acne, gastrointestinal reaction, joint pain, and blood reduction compared with WCM. However, life-threatening adverse effects were not mentioned in all of these studies.  The full and validated botanical names of herbs were generalized in Table 5.

The Possible Mechanisms of CHM for WD
The possible mechanisms of the most frequently used herbs and the main active ingredients are as follows: (1) Curcumin: an active ingredient from commonly used herbs like Rhizoma Curcumae Longae, Rhizoma Curcumae, Radix Curcumae and Radix Curcumae can partially restore protein expression of most ATP7B mutants to restore functional copper export (van den Berghe et al., 2000;Zhang et al., 2011; European Association for Study of Liver, 2012). Furthermore, curcumin is an ideal antioxidant, an effective scavenger of reactive oxygen species (Samarghandian et al., 2017), and it exerts anti-fibrotic effect through regulating hepatic stellate cells (HSCs) function (Jin et al., 2016;Liu et al., 2016;Mustafa, 2016).

Summary of Evidence
Eighteen RCTs involving 1,220 patients suffering from WD were identified. The main findings of this study were that CHM adjuvant therapy could increase 24 h urinary copper excretion, and improve liver function and the total clinical efficacy rate for WD. Two trails Wang, 2008, 2010) indicated that CHM monotherapy was not superior to the WCM. Eight out of eighteen studies reported no serious adverse events relevant to CHM formulas, indicating that CHM formulas were generally safe and well tolerated for patients with WD. The possible mechanisms are associated with reversing the ATP7B mutants, and exerting anti-oxidation, anti-inflammation and anti-fibrotic effects. Thus, the findings of the present study suggested, to a limited extent, that CHM paratherapy can be used for WD according to the methodological flaws, whereas the beneficial use of CHM monotherapy for WD still lacks evidence.

Limitations
There are several limitations in the primary studies. Firstly, although we included RCTs, some inherent and methodological weaknesses still existed in the primary studies: only 2 trials provided sufficient information on how the random allocation was generated, while none of the other trials included reported the allocation concealment. No study employed the blinding procedure, making it difficult to bias results intentionally or unintentionally and to help ensure the credibility of study conclusions. A placebo effect is conceptually defined as the beneficial effect associated with an intervention that does not include the presumed active ingredients; however, CHM placebo are hard to mimic identical interventional herbal prescription due to the fact that CHM is special in color, smell and taste. Thus, placebo-controlled randomized trials are well-recognized method when evaluating the efficacy of CHM treatment. In addition, most trials are without calculating the formal pretrial sample size. The trials with inadequate sample sizes seem to be one risk in exaggerating intervention benefits. Secondly, WD is a chronic disease, which needs life-long treatments. Long-term efficacy and safety are important assessments to determine the clinical effectiveness of an agent in treatment. However, in the present study, treatment duration ranged from 28 to 90 days. Long-term safety of CHM for WD could not be determined because duration of treatment is short and dropouts were only reported in one study. According to other clinical trials for WD Weiss et al., 2015;Nicholl et al., 2017), it is recommended that the treatment duration of further trials must not be >60 days, and must last more than 1 year. Thirdly, clinical heterogeneity would be very significant due to the variations in study quality, intervention of CHM prescriptions, comparators, and outcome measures. Owing to being highly variable in composition and dosage of CHMs, it is difficult to assess the efficacy of a specific CHM by performing pooling analysis. Fourthly, all trials were conducted in China, which may limit the generalizability. Further international multicenter RCTs of CHM for WD are needed, in order to generalize the results worldwide.

Implications for Practice
Use of CHM for WD patients has increased in the past decades. However, the choice of CHM is mainly empirical and lacking consensus among clinical doctors. The available evidence from the present study supported, to a limited extent, that CHM paratherapy can be used for patients with WD but should not be recommended as monotherapy in WD. In addition, the most frequently used herbs selected by the present study should be considered as herbal prescription for WD and as a candidate for further clinical trials.

Implications for Research
In the present study, we identified an area that is worthy of further study. Firstly, the potential benefit of CHM as an adjunct treatment for WD still needs to be further confirmed by high-quality RCTs. Thus, we recommend that CONSORT 2010 statement (Schulz et al., 2010), CONSORT for CHM Formulas (Cheng et al., 2017), and RCTs investigating CHM (Flower et al., 2011) should be used as the guidelines when the designing, registering and reporting of further RCTs. Secondly, WD was thought of as a "rare" autosomal disorder by neurologists, and it proved difficult to conduct large sample RCT. However, this review identified 1,220 subjects with WD from 1997 to 2016. If the primary clinical data of all RCTs were recorded in standard, the evidence would be more reliable. Thus, it is necessary to promote clinical data sharing, as has been suggested by the International Committee of Medical Journal Editors (ICMJE) (Taichman et al., 2017). WD is caused by ATP7B mutations, resulting in copper accumulation and toxicity. The possible mechanisms of CHM for WD not only involve the targets of the ATP7B gene, but also the multiple targets of copper accumulation in various tissues and organs. Curcumin and P-coumaric acid were reported to reverse the ATP7B function defect. Curcumin could partially restore protein expression by directly enhancing the protein expression of mutant ATP7B with residual copper export activity (van den Berghe et al., 2000;Zhang et al., 2011; European Association for Study of Liver, 2012). The EASL Guidelines recommended that treatment with curcumin might be a novel therapeutic strategy in WD (European Association for Study of Liver, 2012). Pcoumaric acid, another ingredient of herbs, can also reverse the ATP7B function defect via a different mechanism by regulating pre-mRNA splicing (Lin et al., 2015).
Frontiers in Pharmacology | www.frontiersin.org including inhibition of proliferation and fibrogenesis of HSCs, and regulation of the antioxidant system and lipid peroxidation. Thus, CHM is likely to be useful as a multi-targeting therapy for WD pathogenesis (Figure 6).

CONCLUSION
Despite the apparent positive results, the present evidence supports, to a limited extent because of the methodological flaws and CHM heterogeneity, that CHM paratherapy can be used for patients with WD but should not be recommended as monotherapy in WD. The possible mechanisms involved are associated with reversing the ATP7B mutants, and exerting antioxidation, anti-inflammation and anti-hepatic fibrosis effects. Further rigorous RCTs, focusing on an individual CHM formula for WD, are warranted.

AUTHOR CONTRIBUTIONS
G-QZ contribute as the senior authors and the principal investigator (PI) of this study. M-BX, P-QR, and T-YJ wrote the first draft of the manuscript and contributed to the overall design. G-QZ refined the study. P-PZ and H-YL identified reviewed studies for eligibility and performed the meta-analysis of data. All authors read, critically reviewed and approved the final manuscript.