A minireview on phytochemical and medicinal properties of Clinacanthus nutans

Clinacanthus nutans (Burm.f.) Lindau has attracted considerable attention in the past two decades, particularly in Southeast Asia, due to its medicinal properties. It has broadly been used as a folk medicine to treat various illnesses ranging from snake bites, viral infection, inflammation, diabetes, and cancers. Natural phytochemical constituents isolated from this plant possess medicinal properties that can help maintain general health and prevent or treat certain diseases. This paper aims to provide an updated overview of its ethnomedicinal uses, phytochemical constituents, pharmacological activities, and toxicity.


INTRODUCTION
Despite tremendous advancement in therapeutic intervention, plant-based traditional medicines remain popular worldwide for treating various ailments. Medicinal plants represent a vast reservoir of bioactive molecules that are invaluable for treating a broad spectrum of diseases and promising sources for discovering interesting compounds for therapeutic intervention. Nevertheless, only about 15% of plant species have been thoroughly studied for their potential medicinal values (Süntar, 2020).
Clinacanthus nutans can grow up to 1 m in height with cylindrical, striate, and hairless stems (Fig. 1). The stems are small, soft, thin, and slightly curved, resembling an elephant trunk. The leaves are simple, opposite to its leaf blade narrowly elliptic and oblong or lanceolate shapes. Its leaf surface is pubescent when young and becomes glabrescent at maturity. The flowers are yellowish and are formed in clusters at the top branches and branchlets (Shim et al., 2013;Yahaya et al., 2015).

Ethnobotanical uses
Clinacanthus nutans is a well-known folk medicine, especially in Thailand and Malaysia. It has reportedly been used for various ailments such as snake bites, viral infection [herpes simplex viruses (HSV-1 and HSV-2), varicella-zoster virus (VZV), and human papillomavirus (HPV)], and cancer (Kamarudin et al., 2017;Kongkaew and Chaiyakunapruk, 2011;Kunsorn et al., 2013). Apart from that, C. nutans extracts are also useful in treating inflammation disorders such as swelling, bruises, strains, sprains of injuries, and rheumatism. It has also been used for gastrointestinal diseases, dysuria, diabetes, fever, and regulating the menstrual cycle (Shim et al., 2013).
Its fresh leaves are commonly served alone or together with herbs as tea because of their nutritional and antioxidant properties. Besides that, it is also used as a home remedy for cancer patients. In Thailand, the alcoholic extract was applied externally for skin irritations, snake/insect bites, and lesions caused by HSV and VZV (Sakdarat et al., 2009). The leaves could be consumed alone or mixed with other juices (Aslam et al., 2014) for general well-being. The combination of leaves and stem was also used to make an infusion or decoction to treat hepatitis infection (Teshima et al., 1998). The lotions and creams made solely from the plant had been reported by Sakdarat et al. (2006) to treat minor skin inflammation and insect bites.
In Malaysia, cancer patients have claimed their recovery from cancer illnesses after drinking a decoction made from C. nutans leaves over a certain period. Currently, various testimonies asserted the effectiveness of this herb for different cancer treatments and prevention. Due to the lack of scientific study and evidence, tremendous efforts have been invested in understanding and deciphering the molecular interactions of the phytochemical compounds and their molecular targets in the last few decades.
Chemical constituents with the established biological functions or potential therapeutic benefits are summarized in Table 1. Phytochemicals such as catechin, betulin, lupeol, kaempferol, squalene, and vitamin E are known to possess antioxidant, anticancer, and anti-inflammatory activities. Molecular docking analysis has predicted several bioactive compounds that could potentially be used in preventing disorders linked to hyperuricemia, wound healing, and hyperlipidemia. Among them were clinacoside A-C, cycloclinacoside A1, shaftoside, vitexin, orientin, isovitexin, and isoorientin (Narayanaswamy et al., 2016).

Pharmacological activities
Traditionally, C. nutans is a folk medicine for alleviating various health complications and ailments. In Thailand, numerous studies have shown that C. nutans leaf extracts exhibited excellent biological activities against viruses, inflammation, and cancer. In clinical trials, creams blended with the plant extract showing positive effects in alleviating patients with HSV and VZV infections (Charuwichitratana et al., 1996). Other studies also discovered that the medicinal products from this plant had replaced acyclovir topical to treat herpes simplex and herpes zoster in hospitals (Kongkaew and Chaiyakunapruk, 2011;Vachirayonstien et al., 2010). Sriwanthana et al. (1996) stated that C. nutans was traditionally used in cancer patients as primary complementary or alternative herbal remedies. In Thailand, the aerial parts of the plant prepared in decoction form showed an anticancer effect on KB cells (human nasopharyngeal carcinoma cell line) and mammary cancer-bearing rats by promoting the activity of natural killer cells (Na-Bangchang et al., 2012). People in Malaysia also have the same practice where they mixed C. nutans leaf in various formulations such as herbal or fruit juices. Many of them claimed to have recovered after using it for a certain period (P'ng et al., 2013). Thus, attempts to understand its modes of action are carried out mainly using C. nutans leaf extracts.
Despite controversial findings, some research findings revealed the chemoprevention and chemotherapy potential of C. nutans. For instance, the aqueous extract was found to possess significant antiproliferative activity against cervical cancer (HeLa) and erythroleukemia (K-562), while the chloroform extract showed profound inhibitory effects against K-562 and Raji cells (Yong et al., 2013). However, only Teoh et al. (2017) demonstrated its root extracts to exhibit antiproliferative and proapoptotic activities on breast cancer cell line, MCF-7.
Apart from that, its ethanol leaf extracts were also shown to have protective effects of DNA integrity by retaining the supercoiled structure of plasmid DNA under riboflavin photoreaction treatment (Yuann et al., 2012). Besides that, the leaf extract also elicited antioxidant activity and prevented the rupture of red blood cells induced by free radicals (Pannangpetch et al., 2007).
Male mice repeatedly administrated with the leaf methanol extracts at different concentrations of 250, 500, and 1,000 mg/kg for 14 days continuously showed a significant increase of acetylcholinesterase (AChE) activity in several organs (e.g., heart, liver, and kidney) but not in the brain. This indicated that the extract did not cause neurological dysfunctions in the treated mice (Lau et al., 2014). However, the bioactive compounds that contribute to the activation of AChE remain unknown.
The only polysaccharide-peptide complex reported so far was isolated from the leaves. It was made of 87.25% carbohydrate and 9.37% protein. This complex inhibited the growth of gastric cancer cells (SGC-7901) in a concentrationdependent manner. It also increased the nitric oxide production in RAW264.7 cells, suggesting an immunomodulating effect (Huang et al., 2016).
The metabolomic findings on C. nutans aqueous extracts at the concentrations of 500 and 1,000 mg/kg ameliorated the physiological sickness behavior in lipopolysaccharide-induced rats after 2 weeks. This improvement was correlated with antineuroinflammatory metabolite biomarkers' expression from nuclear magnetic resonance spectra compared to the sera obtained from the control group (Azam et al., 2019). Additional and updated studies supporting the pharmacological actions of C. nutans are deliberated and depicted in Table 2.

Toxicity
Several toxicological assessments of C. nutans extracts have been carried out on animals, but no lethal toxicity was reported so far. P'ng et al. (2013) observed no lethality and abnormal behavior in mice administrated with the methanolic leaf extracts (300, 600 and 900 mg/kg) for up to 14 days. Both treated and control groups showed no significant differences in terms of serum biochemical tests. In another study, the subchronic toxicity of the ethanol leaf extract was assessed in male Sprague Dawley rats for 90 days (Asyura et al., 2016). The results demonstrated hepatotoxicity and renal toxicity with no mortality in rats treated with 125-250 mg/kg of plant extracts. Conversely, Roslan et al. (2017) documented subacute toxicities in the female BALB/c Table 1. Phytochemical compounds found in C. nutans with known biological functions.

Plant part Chemical constituent References
Stem and root Lupeol Dampawan et al. (1977),
Besides increases of reactive oxygen species (ROS) and calcium ion, the upregulation of CHOP and IRE-1α proteins (ER stress) was also observed. Lu et al. (2018) Leaf (water extract) Sonicated water extract had the highest nitric oxide inhibitory effect in lipopolysaccharide-interferon-gammainduced RAW264.7 macrophages. 1 H-NMR metabolomic analysis suggested C-glycosyl flavones abundantly found in this extract plays an important role in anti-inflammatory effect.
Hexane and dichloromethane extracts showed better cytotoxicity effects on MCF-7 but the dichloromethane extract exhibited less inhibitory effect on normal breast cells. Through molecular docking, palmitic acid and linolenyl alcohol in dichloromethane extract were found to have the highest binding affinity with p53-binding protein Mdm-2. Ismail et al. (2020) mice organs after administering 300, 2,000 and 5,000 mg/kg of the ethanol leaf extract for 28 days. The C. nutans methanolic leave extract showed adverse effects on the CYP3A4 enzyme activity of human liver microsomes. If the plant extract is consumed together with a drug metabolized by CYP3A4, it can slow down xenobiotics' metabolism in the body. The xenobiotic accumulation for extended periods may become potentially toxic in the body system (Quah et al., 2017). It was also found that the male and female mice showed no alteration of their body weight after administrated with the methanolic leaf extracts at 1,000 and 2,000 mg/kg. Besides, there were no hematological, biochemical, and histology signs of toxicity after 28 days (Abdulwahid et al., 2018).
The metabolomic analysis carried out using highresolution proton nuclear magnetic resonance ( 1 H-NMR) on the acute toxicity of rats administrated with a single dose of leaf water extract at 5,000 mg/kg for 15 days did not show significant metabolic abnormalities. These findings were in accordance with the results derived from physical, hematological, biochemical, and histopathological observation (Khoo et al., 2018).
On the contrary, Aliyu et al. (2020) suggested that precautions should be taken if they intend to use the plant extract as a health supplement after observing hepatic and kidney toxicities in mice continuously consumed with C. nutans ethanolic leaf extract (1,000 mg/kg) for up to 28 days. Besides, a single dose at 2,000 mg/kg could also cause mild histological changes in the liver and renal with no hematological toxicity.

CONCLUSION
Even though extensive research has managed to shed light on the potential therapeutic values of C. nutans, scientific evidence is still scarce. For instance, many studies, including clinical trials, have shown a promising effect on antiviral activities, but its underlying molecular mechanisms are still unclear. More research focusing on multiple signaling pathways instead of targeting specific biological action will provide a better understanding of how these bioactive compounds exert their biological functions. Further investigations on the chronic toxicity effects of C. nutans plant extract also need to be done to ensure its safe consumption. These comprehensive data are essential in facilitating the discovery of potential drug target(s) and future development of drug(s) derived from C. nutans.

ACKNOWLEDGMENTS
The author thanks Dr. Bonaventure Vun Leong Wan for proofreading the manuscript, Dr. Cheong Bo Eng for providing the photo, and Universiti Malaysia Sabah for the support.

AUTHOR CONTRIBUTIONS
All authors made substantial contributions to conception and design, acquisition of data, or analysis and interpretation of data; took part in drafting the article or revising it critically for important intellectual content; agreed to submit to the current journal; gave final approval of the version to be published; and agree to be accountable for all aspects of the work. All the authors are eligible to be an author as per the international committee of medical journal editors (ICMJE) requirements/guidelines.

CONFLICTS OF INTEREST
The authors report no financial or any other conflicts of interest in this work.

ETHICAL APPROVALS
This study does not involve experiments on animals or human subjects.

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