Coptisine from Coptis chinensis exerts diverse beneficial properties: A concise review

Abstract Coptisine is a natural small‐molecular compound extracted from Coptis chinensis (CC) with a history of using for thousands of years. This work aimed at summarizing coptisine's activity and providing advice for its clinical use. We analysed the online papers in the database of SciFinder, Web of Science, PubMed, Google scholar and CNKI by setting keywords as ‘coptisine’ in combination of ‘each pivotal pathway target’. Based on the existing literatures, we find (a) coptisine exerted potential to be an anti‐cancer, anti‐inflammatory, CAD ameliorating or anti‐bacterial drug through regulating the signalling transduction of pathways such as NF‐κB, MAPK, PI3K/Akt, NLRP3 inflammasome, RANKL/RANK and Beclin 1/Sirt1. However, we also (b) observe that the plasma concentration of coptisine demonstrates obvious non‐liner relationship with dosage, and even the highest dosage used in animal study actually cannot reach the minimum concentration level used in cell experiments owing to the poor absorption and low availability of coptisine. We conclude (a) further investigations can focus on coptisine's effect on caspase‐1‐involved inflammasome assembling and pyroptosis activation, as well as autophagy. (b) Under circumstance of promoting coptisine availability by pursuing nano‐ or microrods strategies or applying salt‐forming process to coptisine, can it be introduced to clinical trial.

with berberine. 13 To date, many investigations have evaluated coptisine's multiple properties, and a review article released in recent year shows coptisine's considerable beneficial functions such as anti-bacterial, gastric mucosa protection and osteoclast differentiation inhibition. 14 However, the intracorporal process of coptisine was not mentioned in this review and the underlying molecular mechanism of its pharmacological activation is not fully understood. As low molecular weight compounds containing nitrogen, isoquinoline alkaloids have been widely developed into various drugs due to their high biological activity. The key findings gathered from the literature of the last two decades are scrutinized in this work, aiming to describe the implications of coptisine in multiple diseases and further provide advice for the clinical use of coptisine and CC.   129

| INTR ACORP OR AL PRO CE SS
During the past decades, many pharmacokinetic studies have been focused on the intracorporal process of formulas like SHXXT and BanXia Xiexin decoctions, 15,16 the main constituents of which were all verified to include coptisine (Chemical structure showed in Figure 1). In rat model administrated with SHXXT, coptisine was not metabolized in blood and could reach hepatic and liver cells as prototype form. 17 To evaluate further coptisine metabolism in liver, a study conducted in zebrafish model demonstrated that coptisine has 4 metabolites and the main metabolic ways include demethylation, hydroxylation, sulphation and glucuronidation. 18 Moreover, coptisine was revealed to be the substrate of P-gp, 19 which to some extent, contributes to the low distribution of coptisine in multiple tissues.

| ANTI -C AN CER PROPERT Y
Numerous researches have verified the vital role of MMPs, MMP-2 and MMP-9 in particular, in promoting the membrane-basement invasion of tumour cells. 22,23 Related to MMPs, the activation of PI3K/ Akt pathway is crucial for the growth and survival of cancer cells and it plays a dominant role in regulating EMT and the following process of migration and invasion. 24 As shown in Figure 3 33,34 In the next study, authors revealed that coptisine and NCI•H1650 cells. [38][39][40] Several studies have established that coptisine exerts ameliorative effect on cancer in in vivo model. Cao  F I G U R E 3 Schematic summaries of coptisine's anti-cancer targets. Coptisine regulates cell cycle and blocks the occurrence of apoptosis and metastasis initiation by modulating the marked targets. Red arrows represent for decreased expression and/or activity; blue arrows represent for increased expression and/or activity

| ANTI -INFL AMMATI ON PROPERT Y
Involved in the pathogenesis of many types of cancer, inflammation is one part of protective biological response to harmful stimuli (damaged cells, pathogens, irritants, etc). Inflammatory transductions depend on cellular pathways, among which NF-κB, MAPK and PI3K/ AKT attract most attention in resent research. 44 NF-κB is a classic pathway and typically activated by LPS. Upon stimulation, TLR-4 directly binds to LPS and then recruits adaptor protein MyD88, resulting in the primary activation of enzyme complex IKK. 45,46 In addition to that, IKK activation is also followed by RIP2/caspase-1 of MAL/caspase-1 interaction. 47,48 MAPK is another key inflammatory signalling pathway, and it consists of three subfamilies, namely p38, JNK and ERK. Accordingly, natural products which exert properties to block inflammatory signalling transduction by inactivating targets Similarly, inhibition of inflammatory process was also observed in animal models including xylene-induced ear oedema, carrageenan-elicited paw oedema, LPS-induced shock, OVA-induced allergic rhinitis and MSU-elicited gouty after coptisine administration. 54 Mechanistically, coptisine (50-200 mg/kg, oral, once daily for 10 days; 10-40 mg/kg, oral, once daily for 7 days; 2.91-11.61 mg/ F I G U R E 4 Schematic summaries of coptisine's anti-inflammatory and CVD protection targets. Coptisine blocks inflammatory response and ameliorates CADs through modulating the marked targets. Red arrows represent for decreased expression and/or activity; blue arrows represent for increased expression and/or activity kg, i.v, single dose, 0-24 hours) diminished cytokine production through blocking inflammatory transduction mediated by the phosphorylation of IKKα/β and MAPK subfamilies, the translocation and degradation of p65 in oedema tissue as well as suppression of NLRP3 inflammasome activation. 50,53,55 Of interest, coptisine (0.97-3.87 mg/kg, i.v; single dose, 0-4 hours) showed no effect on the up-regulation of oedema skin temperature induced by carrageenan subcutaneously injection in rats. 49 Furthermore, there is a study investigating a pharmacokinetic-pharmacodynamic model for coptisine challenge of inflammation in LPS-elicited rats, and authors emphasized early stage of TNF-α response is the key factor of the subsequent inflammatory cascade. 56

| AMELI OR ATIVE EFFEC T ON C VDS
The typical cardiovascular diseases (CVDs) includes heart attack (or myocardial infarction), atherosclerosis, heart failure and stroke. 57   compounds' inhibitory effect on protein kinase C and found that coptisine dose-dependently suppress the activity of protein kinase C. 83 These results showed coptisine's great potential in diabetes treatment. In addition, coptisine (10-40 mg/kg, once daily for 7d) showed anti-ulcer efficacy through the inhibition of p38 MAPK and the activation of Nrf2 signalling pathway. 84,85 Interestingly, the effect of coptisine (0.0025-0.01 mg/mL, Pharmacological research in current years indicates coptisine is a multi-targeting isoquinoline alkaloid (Tables 2 and 3), while there are several aspects need considering before its translation from bench to bedside.

| S TRUC TURE-AC TIVIT Y REL ATIONS HIP
Coptisine is a typical quaternary proberberine alkaloid (QPA) with a parent nucleus of isoquinoline ( Figure 5), which plays a vital role in the secondary metabolism of herbals like CC. 87  anti-malarial activity against plasmodium falciparum while QPAs with a high lipophilicity exerted more potent anti-bacterial activity. 87 It is reported that an aromatic ring C contributes to a higher activity of G-quadruplex induction and stabilization ability. 90   Nitro Ring A Anti-acetylcholinesterase activity was elevated 89 Hydrophilic radical C-13, ring C Anti-malarial activity was improved 87 High lipophilicity C-13, ring C More potent anti-bacterial activity 87 Aromatic Ring C A higher activity of G-quadruplex induction and stabilization ability 90 Hydroxyl C-9, ring D Hydroxyl radical scavenging effect was promoted 91 Methylenedioxy C-9 and C-10, ring D Dioxymethylene Ring D The inhibitory effect of aldose reductase was enhanced 92 Oxidized dioxymethylene Ring A Di-methoxy Ring D Increased LDLR expression and AMPK activation 93 normal IEC-6 cell. 88 More details are yet unclear and investigations are still needed.

| CLINIC AL US E , DOSAG E AND ADVER S E RE AC TIONS
Documented in ancient pharmaceutical books, CC has been used since 2000 years ago in the treatment for ocular inflammation, diarrhoea and damp-heat-caused abdomen disorders, which are also the common indications of CC's clinical use by now. Since CC exerts effect of clearing away damp-induced heat, we can also be informed from some Chinese plant medicine books of its anti-tumour action. 94 However, there is still a long journey to transfer the knowledge to clinical application and CC clinical trial still remains at an early stage. 95 By far, there is yet no record of single-dosed coptisine in clinical, while berberine, the most abundant isoquinoline alkaloid in CC, has a history of treating bacteria-correlative diarrhoeas in the late 1900s. 96 On the other hand, dose-effect relationship determines how well the drug works. In clinical, owing to the affecting factors such as age, disease location, administration route and processing method, CC exhibits a very wide daily single dose range of 1.5-40 g. 97 As for coptisine, shown in Table 5 and coptisine have relatively wide range of safety.We also notice that, even ignoring the distribution loss from blood to tissues, the plasma level of coptisine with the highest dose in animal experiment is in fact, not able to reach the minimum concentration level used in cell experiment, so the main death cause of mice in LD 50 study is probably due to the gastrointestinal toxicity, rather than systemic toxicity.

| FUTURE PROS PEC TS
Chemically modified drug plays a dominant role in clinical because it exerts potent therapeutical effect by affecting accurate and specific target. 56,102 Unfortunately, it meanwhile shows many adverse effects such as unselectively killing normal cells in chemotherapeutics. 103,104 During the past decades, natural products are attracting more and more attention for their preferable treating property with low toxicity. 105 For example, apigenin from Epimedium koreanum Nakai, emodin from Rheum palmatum L, quercetin from Hypericun ascyron L and curcumin from Curcuma louga L are all reported to modulate various chronic diseases within safe dose range. [106][107][108][109] Here in this article, we systematically review the existing literature concerning coptisine's diverse beneficial properties, and this continues to support the recommendation that coptisine can be applied to the treatment for cancer, inflammation, CVDs and metabolic disorders.
The main anti-cancer approaches include (1) invasion and metastasis prevention, (2) apoptosis or (3) autophagy induction, among which (1) and (2) are reported to be successfully achieved by coptisine treatment in many cancer cell lines to date. Apart from mechanisms mentioned above, cellular senescence is another promising approach in anti-cancer therapy. 110 It has been reported that berberine, a natural product which shares similar structure with coptisine, induced apoptosis and premature senescence, respectively, while used in high concentration of shorter treatment and lower concentration over longer period of treatment. 111,112 Therefore, it will be meaningful to evaluate coptisine's effect on cellular senescence of cancer cells.
Another essential issue which needs to be further detected in future investigation is the role of coptisine to act as small-molecule inhibitor of key markers involved in inflammation, CVDs, etc Berberine is revealed to diminish mRNA overexpression of caspase-1 and NLRP3 in MSU-challenged Raw 264.7 cells, and it also regulates pyroptosis in human hepatocellular carcinoma. 113,114 Since caspase-1 is a key marker participating in inflammasome assembling and pyroptosis occurrence, and coptisine displays considerable suppressing effect on NLRP3 inflammasome priming and assembly, another relevant subject for further study can be the role of coptisine as small-molecular inhibitor of caspase-1 and the downstream pyroptosis activation.
Cardiovascular diseases such as hyperlipidaemia and hypertension are global health issue and closely related to metabolic disorder which is accompanied by low-grade chronic inflammation. 115 Similar F I G U R E 6 Recommendations for future investigations on coptisine. Once mitochondrion is damaged, PARK2 binds to PINK1 on the surface of mitochondrial and ubiquitinates mitochondrial outer membrane proteins, which then bind to SQSTM1, a receptor which can interact with LC3. The formation of autophagosome inhibits ROS, the overproduction of which causes NLRP3 inflammasome assembling and the downstream pyroptosis and inflammatory response to coptisine, berberine exerts cardiovascular protection, lipid-lowering, vascular-relaxing and anti-atherosclerosis properties. Besides, berberine also prevents multiple pathophysiologic processes such as myocardial injury, neurohormonal activation and oxidative stress. [116][117][118] Accordingly, further efforts could focus on coptisine's effect on myocardial injury biomarkers (eg cardiac troponins), neurohormonal activation biomarkers (eg norepinephrine, ET-1) and oxidative/nitroxidative stress biomarkers (eg nitrotyrosine, MPO).
Autophagy is involved in the progression of multiple disorders including cancer and CADs. [119][120][121] To date, apart from regulating transduction of pathways such as NF-κB, MAPK and PI3K/AKT, berberine has been verified to mediate mitochondrial-induced apoptosis and protective autophagy in human breast cancer cells, 122 and it also induces autophagy and the downstream NLRP3 inflammasome activation in macrophages. 123 Moreover, berberine ameliorates CADs through triggering autophagy in both Beclin-1-dependent and Beclin-1-independent ways. 124 Since coptisine and berberine exert property of structural homology, the limitation of the existed studies includes the lack of investigation concerning the effect of coptisine on autophagy occurrence, which is closely related to the pathogenesis of multiple cancers, inflammation and CADs (Table 6 and Figure 6).
As mentioned in previous chapters, the plasma concentration of coptisine and other CC isoquinoline alkaloids demonstrates obvious non-liner relationship with dosage, and the low dissolution in intestinal fluid dominantly limits the absorption amount. In recent years, pharmaceutics methods like nano strategies and microrods have been employed to promote the intestinal dissolution of berberine.
Given the similar parent structure shared by berberine and coptisine, further study is advised to focus on new pharmaceutics strategy which is able to improve coptisine's dissolve rate.
To sum up, coptisine is a promising drug with multiple targets, while there is still a knowledge gap before coptisine meets the requirements to be introduced to clinic and further applied to the prevention and therapy of diseases such as cancer, inflammation, anti-bacteria and CVDs. Besides, more investigation is needed to promote coptisine's bioavailability and meanwhile reach the balance between toxicological safety and therapeutic efficacy.

ACK N OWLED G EM ENTS
This work is supported by grants from the National Natural Science

CO N FLI C T O F I NTE R E S T S
The authors declare no conflicts of interest.

DATA AVA I L A B I L I T Y S TAT E M E N T
No data, models or code was generated or used during the study.