Traditional Uses, Botany, Phytochemistry, Pharmacology, Pharmacokinetics and Toxicology of Xanthium strumarium L.: A Review

Xanthium strumarium L. (Asteraceae) is a common and well-known traditional Chinese herbal medicine usually named Cang-Er-Zi, and has been used for thousands of years in China. The purpose of this paper is to summarize the progress of modern research, and provide a systematic review on the traditional usages, botany, phytochemistry, pharmacology, pharmacokinetics, and toxicology of the X. strumarium. Moreover, an in-depth discussion of some valuable issues and possible development for future research on this plant is also given. X. strumarium, as a traditional herbal medicine, has been extensively applied to treat many diseases, such as rhinitis, nasal sinusitis, headache, gastric ulcer, urticaria, rheumatism bacterial, fungal infections and arthritis. Up to now, more than 170 chemical constituents have been isolated and identified from X. strumarium, including sesquiterpenoids, phenylpropenoids, lignanoids, coumarins, steroids, glycosides, flavonoids, thiazides, anthraquinones, naphthoquinones and other compounds. Modern research shows that the extracts and compounds from X. strumarium possess wide-ranging pharmacological effects, including anti- allergic rhinitis (AR) effects, anti-tumor effects, anti-inflammatory and analgesic effects, insecticide and antiparasitic effects, antioxidant effects, antibacterial and antifungal effects, antidiabetic effects, antilipidemic effects and antiviral effects. However, further research should focus on investigating bioactive compounds and demonstrate the mechanism of its detoxification, and more reasonable quality control standards for X. strumarium should also be established.


Introduction
Since 1963, the fruits of Xanthium strumarium L. have been listed in the Pharmacopoeia of the People's Republic of China (CH.P), and currently over 60 formulas containing the fruits of X. strumarium have been applied for treating various diseases, including rhinitis, nasal sinusitis, headache, gastric ulcer, urticarial, rheumatism, bacterial and fungal infections, and arthritis [1][2][3]. So far, many studies have been devoted to the pharmacological and phytochemical studies of X. strumarium, and more than 170 chemical compounds have been isolated and identified from this plant, including sesquiterpene lactones, phenols, glycoside, alkaloids, fatty acid and others [4]. In addition, increasing evidence has indicated that X. strumarium possesses a wide spectrum of pharmacological activities including This plant is widely distributed all over the world, including Russia, Iran, India, North Korea and Japan. It is native to China and widely distributed in the area of Northeast China, Southwest China, North China, East China and South China. It often grows in plains, hills, mountains and wilderness roadsides. The flowering time ranges from July to August, and fruiting stage lasts from September to October in China [1].

Lignanoids and Coumarins
In recent years, some studies found that X. strumarium contain lignanoids and coumarins, moreover, 21 lignanoids and four coumarins have been discovered in this plant and are displayed in Figures 5 and 6. In 2017, xanthiumnolic B (100) was found from the fruits of X. strumarium and its anti-inflammatory activity has been demonstrated [40]. Later, 14 lignanoids were also isolated from the fruits of X. strumarium, including (

Glycosides
In 1962, Song et al. isolated a toxic glycoside component named AA 2 from the fruits of X. strumarium, which has been authenticated as atractyloside (142) by Wang in 1983 [49,59]. Subsequently, John et al. found another toxic ingredient known as carboxyatractyloside (143) in 1975 [50]. Research showed that the content of atractyloside in X. strumarium could be reduced after stir-flying, and its toxicity could be reduced. [60] Lately, seven other glycosides were separated from the fruits of X. strumarium, such as 3β-norpinan-2- [51], and all glycosides are displayed in Figure 8.

Glycosides
In 1962, Song et al. isolated a toxic glycoside component named AA2 from the fruits of X. strumarium, which has been authenticated as atractyloside (142) by Wang in 1983 [49,59]. Subsequently, John et al. found another toxic ingredient known as carboxyatractyloside (143) in 1975 [50]. Research showed that the content of atractyloside in X. strumarium could be reduced after stirflying, and its toxicity could be reduced. [60] Lately, seven other glycosides were separated from the fruits of X. strumarium, such as 3β-norpinan-2- (149), everlastoside C (150) [51], and all glycosides are displayed in Figure 8.

Other Compounds
Apart from these major types of phytochemical compounds mentioned above, there are some other chemical ingredients isolated from X. strumarium, including 5-methyluracil (167), uracil (168)

Other Compounds
Apart from these major types of phytochemical compounds mentioned above, there are some other chemical ingredients isolated from X. strumarium, including 5-methyluracil (167), uracil (168) Figure 11. Chemical structures of the anthraquinones and naphthoquinones in X. strumarium.

Anti-AR Effect
X. strumarium is a traditional medicine widely used in the treatment of nasal diseases, especially allergic rhinitis (AR). In modern pharmacological study, the mechanism of X. strumarium in treating AR has been studied extensively. In 2003, it was reported that WEX inhibited compound 48/80 (C 48/80)-induced systemic anaphylaxis in mice (0.01 to 1 g/kg, p.o.), and the mechanism may be related to the inhibition of histamine and TNF-α released from rat peritoneal mast cells (RPMC) [61,62]. In 2008, Zhao et al. found that WEX (0.25-1 mg/mL) can modulate the human mast cell-mediated and peripheral blood mononuclear cell (PBMNC)-mediated inflammatory and immunological reactions which induced by pro-inflammatory cytokines including interleukin (IL)-4, IL-6, IL-8, GM-CSF and TNF-α [63]. Furthermore, the MEX is found to possess the inhibitory effect on the activation of C 48/80 stimulated mast cells, and the mechanism was correlated to inhibit Ca 2+ uptake and histamine release, and increase cAMP in RPMC [64]. In addition, in 2014, Peng et al. demonstrated that the caffeoylxanthiazonoside (CXT) (5, 10, 20 mg/kg, p.o.) isolated from the fruits of X. strumarium was helpful to alleviate the nasal symptoms of ovalbumin (OVA) induced AR rats via anti-allergic, downregulating IgE, anti-inflammatory and analgesic properties [65].

Anti-Tumor Effect
Anti-tumor effects are also regarded as primary pharmacological properties of X. strumarium, and have been extensively investigated in lung cancer, breast cancer, cervical cancer, colon cancer, liver cancer, meningioma, and leukemia.

Anti-AR Effect
X. strumarium is a traditional medicine widely used in the treatment of nasal diseases, especially allergic rhinitis (AR). In modern pharmacological study, the mechanism of X. strumarium in treating AR has been studied extensively. In 2003, it was reported that WEX inhibited compound 48/80 (C 48/80)-induced systemic anaphylaxis in mice (0.01 to 1 g/kg, p.o.), and the mechanism may be related to the inhibition of histamine and TNF-α released from rat peritoneal mast cells (RPMC) [61,62]. In 2008, Zhao et al. found that WEX (0.25-1 mg/mL) can modulate the human mast cell-mediated and peripheral blood mononuclear cell (PBMNC)-mediated inflammatory and immunological reactions which induced by pro-inflammatory cytokines including interleukin (IL)-4, IL-6, IL-8, GM-CSF and TNF-α [63]. Furthermore, the MEX is found to possess the inhibitory effect on the activation of C 48/80 stimulated mast cells, and the mechanism was correlated to inhibit Ca 2+ uptake and histamine release, and increase cAMP in RPMC [64]. In addition, in 2014, Peng et al. demonstrated that the caffeoylxanthiazonoside (CXT) (5, 10, 20 mg/kg, p.o.) isolated from the fruits of X. strumarium was helpful to alleviate the nasal symptoms of ovalbumin (OVA) induced AR rats via anti-allergic, down-regulating IgE, anti-inflammatory and analgesic properties [65].

Anti-Tumor Effect
Anti-tumor effects are also regarded as primary pharmacological properties of X. strumarium, and have been extensively investigated in lung cancer, breast cancer, cervical cancer, colon cancer, liver cancer, meningioma, and leukemia.
In 2007, by using CellTiter 96 assay in vitro, Ramı'rez-Erosa et al. found that xanthatin and xanthinosin, two sesquiterpene lactones isolated from the burs of X. strumarium, obviously restrain the proliferation of breast cancer MDA-MB-231 cells with the IC 50 values of 13.9 and 4.8 µg/mL, respectively [71]. Furthermore, Takeda et al. studied the mechanism of xanthatin against breast cancer MDA-MB-231 cells in 2011, and the results indicated that xanthatin (5-25 µM) inhibits cell growth via inducing caspase independent cell death which were irrelevant with FTase inhibition [72]. In addition, xanthatin (2.5-10 µM) can also up-regulate GADD45 γ tumor suppressor gene, and induce the prolonged expression of c-Fos via N-acetyl-L-cysteine-sensitive mechanism [73,74]. In 2016, the anti-tumor activity of EEXA on MFC7 cells was reported as well, with an IC 50 value of 70.6 µg/mL [70].
In  [20]. Simultaneously, fructusnoid C (IC 50 = 7.6 µM) also reported to exhibit cytotoxic effects on AGS cells [79]. EEXA and CFEEXA have been identified as the active ingredients against the growth of CT26 cells with IC 50 values of 58.9 and 25.3 µg/mL, respectively [70].
Furthermore, the anti-tumor effects of X. strumarium on liver cancers have also been reported in recent years. In 2013, Wang et al. found that the 1β-hydroxyl-5α-chloro-8-epi-xanthatin possessed significant in vitro cytotoxicity with an IC 50 value of 5.1 µM against SNU387 cells [25]. Later, in 2017, the cytotoxic effects of MEX and EAFMEX on HepG2 cells were verified as LC 50 (Lethal Concentration 50) values of 112.9 and 68.739 µg/mL [80]. Furthermore, Liu et al. demonstrated that xanthatin (5-40 µM) can induce HepG2 cells apoptosis by inhibiting thioredoxin reductase and eliciting oxidative stress [76].
Additionally, an investigation in 1995 indicated that Xanthatin and 8-epi-xanthatin both have cytotoxic effects on SK-MEL-2 cells with ED 50 values 0.5 and 0.2 µg/mL, respectively [17]. In 2012, the EEXS showed notable inhibitory activity on Mel-Ab cells through downregulation of tyrosinase via GSK3β phosphorylation at concentrations of 1-50 µg/mL [81]. Later, in 2013, Li et al. reported the anti-tumor effects of xanthatin both in vitro and in vivo. Previous results showed that xanthatin (2.5-40 µM) possess a remarkable anti-proliferative effect against B16-F10 cells, and the related mechanism probably associated with activation of Wnt/β-catenin pathway as well as inhibition of angiogenesis. Meanwhile, the in vivo evidence in mice (xanthatin, 0.1-0.4 mg/10 g, i.p.) also verified the results mentioned above [82].
In 1994, DFEEXA was reported to be toxic to leukemia P-388 cells with an IC 50 value of 1.64 µg/mL [83]. In addition, results of Nibret et al. showed that xanthatin has significant cytotoxic on HL-60 cells in 2011 [84]. Another report in 2017 reported that both MEX and EAFMEX have inhibitory effects on Jurkat cells, and EAFMEX showed higher toxicity to Jurkat cells when compared to MEX [80].
Besides, in 1995, Ahn et al. found that xanthatin and 8-epi-xanthatin have cytotoxic effects on CNS carcinoma XF-498 cells, and the ED 50 values were 1.7 and 1.3 µg/mL, respectively [17]. In 2013, Pan et al. reported that WEX can cause significant cytotoxic effects on arcoma S180 cells in vivo (S180 cells bearing mice, 5-20 g/kg) [85]. The in vitro anti-proliferative activity of CEXR and MEXR on laryngeal cancer HEP-2 cells were implemented at doses of 12.5-100 µg/mL, and the two extracts of X. strumarium showed potent cytotoxic activities against the HEP-2 cells [86].

Anti-Inflammatory and Analgesic Effects
In 2004, it was reported that WEX (10, 100 and 1000 µg/mL) inhibited inflammatory responses in Lipopolysaccharide (LPS)-stimulated mouse peritoneal macrophages via decreasing IFN-γ, LPS-induced NO production and TNF-α production in a dose dependent manner [87].  [89]. By using LPS inhibition assay and animal model of inflammation (carrageenan induced hind paw edema), the MEXL (100, 200 and 400 mg/kg) showed obvious anti-inflammatory activity both in vitro (IC 50 = 87 µg/mL) and in vivo [90]. A report in 2015 showed that MEXR (50-400µg/mL) can suppress inflammatory responses via the inhibition of nuclear factor-κB (NF-κB) and signal transducer and activator of transcription 3 (STAT3) in LPS-induced murine macrophages [91]. Moreover, the WEX was found to restrain LPS-induced inflammatory responses through suppressing NF-κB activation, inhibiting JNK/p38 MAPK phosphorylation, and enhancing HO-1 expression in macrophages [92]. In 2016, Hossen et al. demonstrated that the inhibitory effect of MEX on the inflammatory disease possibly related to signaling inhibition of MAPK and AP-1 [93]. In another study, Hossen et al. found the potential anti-inflammatory activity of MEXA on LPS-treated macrophages and an HCl/EtOH-induced mouse model of gastritis by inhibiting PDK1 kinase activity and blocking signaling to its downstream transcription factor, NF-κB [94]. Later, in 2017, Jiang et al. found a new phenylpropanoid derivative named Xanthiumnolic E isolated from X. strumarium, which has notable inhibitory effect on LPS-induced nitric oxide (NO) production with IC 50 value of 8.73 µM [26].
Additionally, X. strumarium was confirmed to inhibit some other kinds of inflammatory and painful diseases. In 2011, Huang et al. suggested that WEX inhibited the development of paw edema induced by carrageenan, and exhibited inhibitory activity on acetic acid effect and reduced the formalin effect at the late-phase (0.1, 0.5 and 1.0 g/kg, p.o.) [95]. In addition, the NFEEX at doses of 0.5, 0.75 and 1.0 mg/ear showed strong anti-inflammatory activity in the croton-oil-induced ear edema test, and reduced the amount of writhing induced by acetic acid in mice in a dose-dependent manner (100, 200 and 400 mg/kg) [96]. A report in 2011 demonstrated the anti-inflammatory activity of xanthatin by inhibiting both PGE 2 synthesis and 5-lipoxygenase activity at doses of 100 and 97 mg/mL, respectively [84]. Furthermore, Park et al. first explained the anti-inflammatory mechanism of EEX, which inhibited TNF-α/IFN-γ-induced expression of Th2 chemokines (TARC and MDC) by blocking the activation of the NF-κB, STAT1 and ERK-MAPK pathways in HaCaT keratinocytes [97]. The hot plate test, acetic acid induced writhing test and formalin test were applied to evaluate the analgesic activity of EEX, and it showed significant analgesic activity at concentrations of 250 and 500 mg/kg body weight [98].

Insecticide and Antiparasitic Effects
In 1995, Talakal et al. reported that EEXL possess anti-plasmodial activity against Trypanosoma evansi both in vitro and in vivo. The EEXL exhibited trypanocidal activity at all the four tested doses at 5, 50, 500 and 1000 µg/mL in vitro, and it can significantly prolong the survival period of the T. evansi infected mice at concentrations of 100, 300 and 1000 mg/kg [99]. In 2011, xanthatin was demonstrated to be the dominating insecticidal active compound against Trypanosoma brucei brucei with an IC 50 value of 2.63mg/mL and a selectivity index of 20 [84]. In addition, Go¨kce et al. showed that MEX exhibited both ingestion toxicity and ovicidal activity to Paralobesia viteana with an LC 50 of 11.02% (w/w) [100]. In 2012, by using schizont inhibition assay, the anti-plasmodial activity of EEXL against Plasmodium berghei was assessed, and it showed significant activity (IC 50 = 4 µg/mL) and high selectivity index in vitro [101]. Later, in 2014, Roy et al. found that WEXL had distinct insecticidal properties against Callosobruchus chinensis with strong toxicity, repellent properties, inhibited fecundity and adult emergence of the insects at 1%, 2% and 4% concentrations [102]. Moreover, it is reported that EEX revealed anti-nematode activity against Meloidogyne javanica in inhibiting egg hatching and inducing mortality among second stage juveniles (J2s) [103]. Furthermore, the effect of MEX on the mortality rates of Aedes caspius and Culex pipiens were investigated, and the results revealed that the LC 50 values of MEX were found to be 531.07 and 502.32 µg/mL against A. caspius and C. pipiens, respectively [80].

Antioxidant Effect
In 2010, it was reported that CEXR and MEXR showed significant free radical scavenging activity by 1,1-diphenyl-2-picrylhydrazyl (DPPH) method with LC 50 values of 10.28 and 40.40 µg/mL, respectively [86]. After administration of PEEXW (250 and 500 mg/kg, p.o., for 20 days), the contents of superoxide dismutase, glutathione peroxidase, glutathione reductase and catalase significantly increased in rats' brain [104]. Later, in 2011, Huang et al. found that WEX exhibited 70.6% to 76.4% and 35.2% to 79.1% scavenging activity on 2,2'-Azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) radicals and DPPH radical scavenging in the concentration of 0.05-0.2 mg/mL; simultaneously, the reducing activity of WEX increased and liposome protection effect enhanced in a concentration-dependent manner with the same doses [95]. In the treatment with the MEXS (100 and 200 mg/kg, p.o. for 10 days), the contents of SOD, CAT, GSH and GPx were obviously increased in the diabetic rats' tissues [105]. Moreover, in 2011, Sridharamurthy et al. evaluated the antioxidant effect of EEXR and CEXR by the scavenging activity of free radicals such as DPPH, super oxide, nitric oxide, and hydrogen peroxide [106]. Results showed that the IC 50 50 values of 85, 72 and 62 µg/mL. In addition, the antioxidant activity was possibly due to the presence of compounds in the extracts like flavonoid and phenolic [107]. In 2015, hexadecanoic acid, α-amyrin and 14-methyl-12,13-dehydro-sitosterol-heptadeconate were isolated from the leaves of X. strumarium, and their antioxidant potential was also evaluated. These three chemical components showed significant antioxidant activity in a dose dependent manner by DPPH and hydroxyl radical assay methods with the IC 50 [32]. A study in 2017 revealed that the EOX displayed notable activity for DPPH radicals with an IC 50 value of 138.87 µg/mL [108]. Furthermore, the antioxidant effects of the MEX obtained by the response surface methodology were measured by the scavenging activity towards the DPPH radical and Ferric ion reducing antioxidant power (FRAP). These results showed that methanol concentration and solid to solvent ratio were demonstrated to possess obvious effects on DPPH and FRAP values [28].

Antibacterial and Antifungal Effects
In 1983, Mehta et al. reported that the WEXFT possessed antimicrobial properties against Vibrio cholera [109]. Later, a study in 1997 revealed that the xanthatin isolated from the leaves of X. strumarium had notable potent activities against Staphylococus epidermidis, Bacillus cereus, Klebsiella pneumoniae, Pseudomonas aeruginosa and Salmonella fyphi with minimum inhibitory concentration (MIC) values of 31.3, 62.5, 31.3, 125 and 125 µg/mL, respectively [110]. In addition, it is reported that MEXL (500 and 100 mg/mL) exhibited strong activity against K. pneumoniae, Proteus vulgaris, P. aeruginosa, Pseudomonas putida, Salmonella typhimurium, B. cereus, Bacillus subtilis and S. epidermidis [111]. In 2015, Chen et al. also reported that β-sitosterol and β-daucosterol isolated from the X. strumarium have significant inhibitory effects against Escherichia coli, with MIC values of 0.17 and 0.35 mg/mL, respectively [112]. By using the disc diffusion method, Devkota et al. determined the antibacterial activity of MEXL and WEXL, and results showed that the two extracts inhibited growth towards K. pneumoniae, Proteus mirabilis, E. coli, B. subtilis, Enterococcus faecalis and Staphylococcus aureus at concentrations of 50,100,150,200 and 250 mg/mL [113]. Moreover, Sharifi-Rad et al. revealed that EOXL can significantly suppress the growth of S. aureus, B. subtilis, K. pneumoniae and P. aeruginosa with MIC values of 0.5, 1.3, 4.8 and 20.5 µg/mL, respectively; additionally, EOXL (30, 60 and 120 mg/mL) also exhibited obvious antibacterial activity against Shiga toxin-producing Escherichia coli [114,115]. Furthermore, Wang et al. revealed that WEX possessed antibacterial potentials against S. aureus and E. coli with MIC values of 31.25 and 7.81 mg/mL, respectively [116]. Using the disk diffusion, the antibacterial activity of EOXF on Rathayibacter toxicus and Pyricularia oryzae was evaluated, and the MIC values were 25 and 12.5 µg/mL, respectively [108].
Similar to the antibacterial potentials, the antifungal activities of X. strumarium were also deeply investigated. In the year of 2002, Kim et al. found an antifungal constituent from X. strumarium, which was named deacetylxanthumin. It can inhibit mycelial growth and zoospore germination of Phytophthora drechsleri with a MIC value of 12.5 µg/mL [117]. In 2011, Yanar et al. used radial growth technique to test the antifungal activities of MEX against Phytophthora infestans, and the MEX showed the lowest MIC value of 2.0% w/v which was lower than the standard fungicide (Metalaxyl 4% + Mancuzeb 64%, MIC value was 2.5%, w/v) [118]. Later, in 2015, Sharifi-Rad et al. investigated the antifungal ability of EOXL on Candida albicans and Aspergillus niger, and the MIC values were 55.2 and 34.3 µg/mL, respectively [114]. In vitro, using the disk diffusion method, the EOXL exhibited strong inhibition against Pyricularia oryzae and Fusarium oxysporum with MIC values of 12.5 and 50 µg/mL, respectively [108]. Furthermore, the EOXL showed remarkable growth inhibition of a wide spectrum of fungal strains, such as A. niger, Aspergillus flavus, F. oxysporum, Fusarium solani, Alternaria alternata and Penicillium digitatum with both MIC and MBC (minimum bactericidal concentration) values of 8 µg/mL [119].

Antidiabetic Effect
In 1974, Kupiecki et al. found that the WEX (15 and 30 mg/kg, i.p.) exhibited potent hypoglycemic activity in normal rats in a dose-dependent manner [120]. In 2000, the antidiabetic effect of caffeic acid isolated from X. strumarium was investigated on both streptozotocin-induced and insulin-resistant rat models. The results showed that caffeic acid (0.5-3.0 mg/kg, i.v.) can decrease the plasma glucose level via increasing the glucose utilization [121]. In 2011, Narendiran et al. found that MEXS at the doses of 100 and 200 mg/kg (p.o., for 30 days) had remarkable diabetic activity in normal-glycemic and streptazocin induced hyperglycemic rats [105]. A report in 2013 demonstrated that the methyl-3,5-di-O-caffeoylquinate showed strong ability to counteract diabetic complications via competitive inhibition of aldose reductase (AR) and galactitol formation in rat lenses [47]. In addition, it is reported that the CFMEXL exhibited notable inhibitory activity on α-glucosidase enzyme with the IC 50 value of 72 µg/mL [122]. Similarly, another study found that MEX also had a strong α-glucosidase inhibitory effect with IC 50 value of 15.25 µg/mL [28].

Antilipidemic Effect
Recently, investigations into the antilipidemic effects of X. strumarium have been conducted. In 2011, the CEXR and EEXR were evaluated for anti-lipidemic activity in Triton WR-1339 induced hyperlipidemia in Swiss albino rats. The results showed that CEXR and EEXR (200 and 400 mg/kg p.o.) can significantly decrease the contents of plasma cholesterol, TG, LDL, and VLDL and increase plasma HDL levels, which was possiblely related to their significant antioxidant activity [106]. Later, in 2016, Li et al. found that WEX (570 and 1140 mg/kg, p.o., for 6 weeks) could improve the synthesis of fatty acid and TG, thus decreased the circulating free fatty acid (FFA) levels, indicating that WEX is involved in solving the abnormality of FFA in the circulation, which is executed by promoting the storage of the excess fat, rather than the elimination of added fat [123]. Furthermore, after treatment with WEX (3.7 and 11.11 g/kg, p.o., for 4 weeks), the blood glucose, TC, TG, LDLC levels decreased and HDLC levels increased in diabetic mice [124].

Antiviral Activity
In 2009, it was reported that the WEX (0.01, 0.1 and 1.0 g/kg, i.g., for 10 days) possessed antiviral activity against duck hepatitis B virus, and it can delay pathological changes [125]. In addition, five compounds were isolated from the fruits of X. strumarium, and their antiviral abilities were also evaluated. The results indicated that norxanthantolide F, 2-desoxy-6-epi-parthemollin, xanthatin, threo-guaiacylglycerol-8 -vanillic acid ether and caffeic acid ethyl ester exhibited notable activity against influenza A virus with IC 50 values of 6.4, 8.6, 8.4, 8.4 and 3.7 µM, respectively by a cytopathic effect (CPE) inhibition method [13].

Other Pharmacological Effects
Apart from the pharmacological effects displayed above, X. strumarium also possesses some other activities. In 2016, the CXT (10, 20, and 40 mg/kg, i.p.) isolated from fruits of X. strumarium showed significant anti-septic activity in animal models of Cecal ligation and puncture (CLP) operation. Meanwhile, the CXT can increase survival rates of septic mice induced by CLP and decrease TNF-α and IL-6 levels induced by LPS in serum of mice [126]. After treatment with WEX (570 and 1140 mg/kg p.o., for 6 weeks), the glucose tolerance and insulin sensitivity improved, meanwhile, lipogenesis increases and lipid oxidation decreased in the liver of high-fat diet rats [127]. In 2014, Lin et al. demonstrated that the EEX (75 and 300 mg/kg, p.o.) can significantly inhibit paw swelling and arthritic score and increase body weight loss and decrease the thymus index in animal model of rheumatoid arthritis induced by Complete Freund's Adjuvant (CFA) [128]. Moreover, the overproduction of TNF-α and IL-1β was notably suppressed in the serum of all EEX-treated rats. The anti-pyretic activity of MEXW (200 and 400 mg/kg, p.o.) was estimated on yeast induced hyperpyrexia, and it showed significant reduction in elevated body temperature [129]. Using Maximal Electroshock (MES) and Pentylenetetrazole (PTZ) induced seizures models, the anticonvulsant activity of PEEXW was tested, and results showed that PEEXW can reduce the mean duration of extensor phase and delay onset of myoclonic spasm and clonic convulsion of treated groups at doses of 250 and 500 mg/kg [130]. In 2016, Panigrah et al. explored the antiurolithiatic effect of HEEXB, and showed that HEEXB can restore the impairment induced by ethylene glycol including hyperoxaluria, crystalluria, hypocalciuria, polyurea, raised serum urea, creatinine, erythrocytic lipid peroxidise and nitric oxide, kidney calcium content as well as crystal deposition. The mechanism may be related to inhibition of various pathways involved in renal calcium oxalate formation, antioxidant property and down regulation of matrix glycoprotein, osteopontin (OPN) [131]. A report in 2012 indicated the antiulcer effect of EEXL in pylorus ligation induced gastric ulcers, and its gastro-protective mechanism may be due to DNA repair, free radical scavenging and down regulation of oxidativenitrosative stress along with cytokines [132]. In an in vivo study, with the CXT treatment (10, 20 and 40 mg/kg, p.o.), the cardiac hypertrophy reduced and fractional shortening (FS), ejection fraction (EF), cardiac output (CO) and heart rate (HR) reversed via suppressing the expression of pro-inflammatory cytokines and the NF-κB signaling pathway [133].

Summary of Pharmacologic Effects
In conclusion, X. strumarium has a wide range of pharmacological effects including anti-AR effects, anti-tumor effects, anti-inflammatory and analgesic effects, insecticide and antiparasitic effects, antioxidant effects, antibacterial and antifungal effects, antidiabetic effects, antilipidemic effects, and antiviral effects. (Table 3). It is noteworthy that the research areas of modern pharmacy primarily focus on chemical components and extracts, which indicated the promising potential of X. strumarium for treating disease. Nevertheless, the chemical constituents and corresponding pharmacological effects of X. strumarium are not systematically sorted out and analyzed. Therefore, it is necessary to investigate the pharmacological activity, structure-activity relationship and mechanism of X. strumarium both in vitro and in vivo experiments in the future.

Pharmacokinetics
Up to now, there are few reports on the pharmacokinetics of the extracts or monomers of X. strumarium. Previous pharmacokinetics studies of X. strumarium mainly focused on its active compounds including xanthatin, cryptochlorogenic acid, and toxic ingredient such as atractyloside. In 2014, a sensitive, specific and rapid ultra-high performance liquid chromatography (UHPLC) tandem mass spectrometry (UHPLC-MS/MS) method was applied to research pharmacokinetic properties of xanthatin in rat plasma. After intravenous injection of xanthatin at a dose of 2.4 mg/200 g, 4.8 mg/200 g and 9.6 mg/200 g, respectively. The t 1/2 of three concentrations were found to be 108. 58 [134].
After intragastric administration of the atractyloside at doses of 11.4, 22.8, and 45.6 mg/kg, the peak time (T max ) values were determined to be 0.38, 1.85, 0.27 h, respectively, the t 1/2 were 13. 64, 9.62, 8.61 h, respectively, and the peak plasma concentration (C max ) values were 41.98, 24.61, 263.40 µg/mL, respectively. In addition, the area under the concentration-time curve (AUC) was also determined, and the AUC 0-t was 132.70, 222.90, and 345.20 µ gh/L. The results showed that the toxicokinetic behavior of atractyloside in rats was non-linear within the experimental dose range [135].
Furthermore, Shen et al. studied the pharmacokinetics of neochlorogenic acid and cryptochlorogenic acid in X. strumarium and its processed products after intragastric administration in rats. The results showed that the T max of neochlorogenic acid and cryptochlorogenic acid in processed fruits of X. strumarium were 2.94 ± 0.18, and 3.00 ± 0.46 h, respectively; the t 1/2 of neochlorogenic acid and cryptochlorogenic acid in processed fruits of X. strumarium were 2.35 ± 1.11, 1.97 ± 0.66 h. Moreover, the T max of neochlorogenic acid and cryptochlorogenic acid in raw fruits of X. strumarium were 3.75 ± 0.46, 2.75 ± 0.27 h, and the t 1/2 of neochlorogenic acid and cryptochlorogenic acid in raw fruits of X. strumarium were 1.70 ± 0.61, 2.12 ± 0.68 h. The neochlorogenic acid in fruits of X. strumarium, after being processed, takes effect quickly and lasts for a long time, while the cryptochlorogenic acid takes effect slowly and has a short action time [136].

Toxicity
In 1990, it was reported that X. strumarium has medium to strong allergenic effects and is poisonous to mammals, and atractyloside and carboxyatractyloside are considered to be the major toxic compounds [137]. X. strumarium is prudently ranked into the medium grade with less toxicity in the Shennong Bencao Jing, a monograph of materia medica. Some other Chinese materia medicas aslo record that X. strumarium possessed mild toxicity, such as Bencao Pinhui Jingyao, Bencao Huiyan. Thus, it is obvious that the ancient Chinese people have had a clear understanding of the toxicity of X. strumarium for a long time [138].
In recent years, many investigations have indicated the toxic effects and related mechanisms of the extracts and monomers of X. strumarium (Table 4). In 2005, Li et al. found that the median lethal concentration (LD 50 ) value of the WEX in mice was 201.14 g/kg (i.g., crude herbs mass equal) [139]. In addition, a report in 2012 suggested that the LD 50 value of the WEX in mice was 167.60 g/kg (crude herbs mass equal, i.g.), however the LD 50 value was 194.15 g/kg (i.g., crude herb mass equivalent) in Fu's research report [140,141]. These changes can be attributed to the toxicity of X. strumarium which varied with the processing method, genetic characteristics and growing conditions [138]. Furthermore, the LD 50 value of the EEX in mice was 275.41 g/kg (crude herbs mass equal, i.g.), which was higher than WEX [140]. Another study showed that the carboxyatractyloside (10-100 mg, i.v.) can induce death in swine [142].
Recently, animal experiments and clinical studies on X. strumarium showed that hepatotoxicity is the main toxicity. In 2011, Wang et al. demonstrated that kaurene glycosides including atractylosid (50-200 mg/kg, i.p.) and carbxyatractyloside (50-150 mg/kg, i.p.) induced hepatotoxicity in mice by way of its induction of oxidative stress as lipid peroxidation in liver [143]. Besides, the chief mechanism of atractyloside poisoning is deemed to be inhibition of the mitochondrial ADP transporter [144]. Furthermore, the WFEEX and NFEEX (0.06, 0.3, 0.7 g/kg, i.g., for 28 days), which have marked hepatotoxicity to rats, can cause pathological changes, such as enlarged hepatic cell space, karyolysis, and inflammatory cell infiltration [145]. Moreover, it has been reported that WEX (21.0 g/kg i.g., for 28 days) significantly increased the content of ALT, AST in mice serum and decreased weight loss [146]. In addition, a study in 2014 found that WEX (7.5, 15.0 and 30.0 g/kg, i.g., for 5 days) can increased the serum ALT, AST, ALP, TBIL levels and the contents of LDL/vLDL, β-HB, glutamate, choline, acetate, glucose in male rats [147]. Finally, in 2018, Zeng et al. indicated that the contents of GLDH, α-GST increased and miRNA-122 decreased after administered WEX (16.7 g/kg i.g., for 7 days), which can be used as sensitive biomarkers for studying the regularity of hepatotoxicity of X. strumarium [148]. Apart from hepatotoxicity, Mandal et al. studied the neurotoxicity of the MEXA in mice and results show that MEXA (100,200, 300 mg/kg) can obviously depress the action of central nervous system [149].  [154] Many other studies have demonstrated that different medicinal parts and extraction parts are also cytotoxic to normal cells including hepatocytes, nephrocytes, ovary cells, etc. The cell inhibition ability of atractyloside on rat hepatocytes was investigated, and the results demonstrated that atractyloside (0.01-0.05 g/L) induced dose-dependent hepatotoxicity according to obvious decreases of cell viability, intracellular gluta-thione (GSH) content and albumin secretion [150]. Furthermore, atractyloside and carbxyatractyloside was reported to improve LDH activity and inhibit cell proliferation at the concentration of 100 µmol/L [147]. In 2013, Yu et al. indicated that WEX at concentrations 100 µg/mL can inhibit growth of HK-2 cells [151]. Moreover, HEXA (25-100 µg/mL) also causes in vitro DNA damage at cytotoxic concentrations through sister chromatid exchanges, chromosome aberrations, and comet assay, meanwhile, it also shows significant reduction in CHO cell viability [152]. In 2016, Su et al. compared the cytotoxicities of the components with different polarities, and study indicated that EAFEEX (IC 50 = 231.1 µg/mL) was the most toxic part [153].
In recent years, few investigations have focused on the toxic effects of X. strumarium on reproduction. In 2014, it was reported that the WEX possessed reproductive toxicity to zebrafish embryos, including decreases in hatch rate, and increases in mortality rate, heart rate and swimming speed [154].

Future Perspectives and Conclusions
In summary, X. strumarium, which possesses anti-AR effects, anti-inflammatory and analgesic effects and anti-tumor effects, has been widely applied to clinical practice in many countries. In the meantime, many modern studies on X. strumarium were also carried out, and its pharmacological activities and chemical compositions have been preliminarily investigated. Nevertheless, how to find out the mechanism of pharmacological activities and its related compounds, develop clinical efficacy of X. strumarium and ensure medication safety are still extremely crucial now.
First, the chemical compounds and pharmacological activity studies of X. strumarium mainly focused on its fruits, but there are few investigations on the roots, leaves, stems and other parts of X. strumarium. In order to enlarge the source domain of the active compounds and maximize the plant utilization rate, it is very critical for researchers to conduct a comprehensive evaluation of other parts of this plant. Second, the fruits of X. strumarium are officially recognized as Cang-Er-Zi in the Chinese Pharmacopoeia (2015 Edition), but many other Xanthium species such as X. mongolicum Kitag, Xanthium spinosum L. and Xanthium canadens Mill were used as X. strumarium alternatives in many areas of China. Therefore, the physical properties, chemical compositions and pharmacological activities should be used to identify and differentiate the different varieties, and it is important to guarantee the safety and efficacy with these herbs to ensure its suitability for clinical use. Third, in China, X. strumarium is commonly used after processing in clinical medicine, but the mechanism of its detoxification still needs further study. The degree of processing depends mainly on the subjective experience of people, and it is difficult to ensure the consistency of the quality of Chinese Medicine. Thus, the intelligent sensory technology combined with artificial intelligence technology, such as machine vision, electronic nose and electronic tongue can be applied to standardize processing methods. Fourth, on the basis of current research progress in vivo and in vitro, many active compounds of X. strumarium have been found and identified, which are probably developed into effective drugs. Among them, xanthatin possessed strong anticancer activity against many kinds of tumors, which means that it has the potential to become an anticancer drug in the future. However, systematic investigations on pharmacokinetics, target-organ toxicity and clinical research of xanthatin will help to develop its bioactive constituents as novel drugs. Fifth, traditional Chinese medicine has the characteristics of multi-component, multi-target and multi-channel, and a single component cannot completely reveal its pharmacological activity. Recently, quality marker (Q-Markers) technologies have started to contribute to scientifically interpreting the correlation degree of effectiveness-material basis-quality control of significant components in traditional Chinese Medicine. For X. strumarium, Q-Markers technologies are able to clarify its possible action, toxicity mechanism and symbolic components, and it is helpful to establish the whole quality control and quality traceability system of X. strumarium.

Conflicts of Interest:
The authors declare no conflict of interest.