Recent Advances in Kaempferia Phytochemistry and Biological Activity: A Comprehensive Review

Abstract

Background: Plants belonging to the genus Kaempferia (family: Zingiberaceae) are distributed in Asia, especially in the southeast region, and Thailand. They have been widely used in traditional medicines to cure metabolic disorders, inflammation, urinary tract infections, fevers, coughs, hypertension, erectile dysfunction, abdominal and gastrointestinal ailments, asthma, wounds, rheumatism, epilepsy, and skin diseases. Objective: Herein, we reported a comprehensive review, including the traditional applications, biological and pharmacological advances, and phytochemical constituents of Kaempheria species from 1972 up to early 2019. Materials and methods: All the information and reported studies concerning Kaempheria plants were summarized from library and digital databases (e.g., Google Scholar, Sci-finder, PubMed, Springer, Elsevier, MDPI, Web of Science, etc.). The correlation between the Kaempheria species was evaluated via principal component analysis (PCA) and agglomerative hierarchical clustering (AHC), based on the main chemical classes of compounds. Results: Approximately 141 chemical constituents have been isolated and reported from Kaempferia species, such as isopimarane, abietane, labdane and clerodane diterpenoids, flavonoids, phenolic acids, phenyl-heptanoids, curcuminoids, tetrahydropyrano-phenolic, and steroids. A probable biosynthesis pathway for the isopimaradiene skeleton is illustrated. In addition, 15 main documented components of volatile oils of Kaempheria were summarized. Biological activities including anticancer, anti-inflammatory, antimicrobial, anticholinesterase, antioxidant, anti-obesity-induced dermatopathy, wound healing, neuroprotective, anti-allergenic, and anti-nociceptive were demonstrated. Conclusions: Up to date, significant advances in phytochemical and pharmacological studies of different Kaempheria species have been witnessed. So, the traditional uses of these plants have been clarified via modern in vitro and in vivo biological studies. In addition, these traditional uses and reported biological results could be correlated via the chemical characterization of these plants. All these data will support the biologists in the elucidation of the biological mechanisms of these plants.

1. Introduction

From the first known civilization, medicinal plants have met primary care and health needs around the world [1,2,3]. Natural products, derived from plants, have enriched the pharmaceutical industry since time immemorial. So far, people of the developing countries depend upon the traditional medicines to cure daily aliments [4]. The medicinal plants are characterized by a diversity of chemical and pharmacological constituents, owing to their complicity and the abundance of secondary metabolites. There are several factors that caused the variations of the secondary metabolites such as ecological zones, weather, climates, and other natural factors via the effects on the biosynthetic pathways [1,2,3].

Zingiberaceae (the ginger family) is distributed worldwide comprising 52 genera and more than 1300 plant species [5,6]. Kaempferia is a diverse family with members distributed widely throughout Southeast Asia and Thailand, including some 60 species [5]. Several Kaempferia species are used widely in folk medicine, including K. parviflora, K. pulchra, and K. galanga, (Figure 1). In Laos and Thai, traditional medicines derived from K. parviflora rhizomes are reported for the treatment of inflammation, hypertension, erectile dysfunction, abdominal ailments [6,7], and improvement of the vitality and blood flow [8]. Japanese use the extract of K. parviflora as a food supplement and for the treatment of metabolic disorders [9]. K. pulchra is used extensively as a carminative, diuretic, deodorant, and euglycemic, as well as for the treatment of urinary tract infections, fevers, and coughs [4]. The rhizomes of K. galanga are used as an anti-tussive, expectorant, anti-pyretic, diuretic, anabolic, and carminative, as well as for the curing of gastrointestinal ailments, asthma, wounds, rheumatism, epilepsy, and skin diseases [10].

Figure 1.

Traditional medicinal used Kaempheria species.

Extracts and purified compounds from select Kaempferia species are used for the treatment of knee osteoarthritis and the inhibition of a breast cancer resistance protein (BCRP), anti-inflammatory, anti-acne, anticholinesterase, anti-obesity-induced dermatopathy, wound healing, anti-drug resistant strains of Mycobacterium tuberculosis, neuroprotective, anti-nociceptive, human immunodeficiency virus type-1 (HIV-1) inhibitory activity, in vitro anti-allergenic, and larvicidal activity against Aedes aegypti [4,6,7,8,9,10,11]. The scientific literature such as, Google Scholar, Scifinder, PubMed, Springer, Elsevier, Wiley, Web of Science, were screened in the period between 1972–2019 in order to collect the up-to-date information of the traditional uses/applications, biological studies, and chemical characterization of Kaempheria species. All these collected data were addressed and summarized in our review article to highlight the potential ethnopharmacological importance of these plants.

2. Materials and Methods

The scientific literature such as Google Scholar, Scifinder, PubMed, Springer, Elsevier, Wiley, Web of Science, etc., including all the traditional uses/applications, biological studies, and chemical characterization of Kaempheria species were collected between 1972–2019. All these collected data were adjusted and summarized in our review article due to the potential ethnopharmacological importance of these plants.

The correlation between the Kaempheria species was evaluated based on the main chemical classes of compounds. The data matrix of seven Kaempferia species (K. angustifolia, K. elegans, K. galanga, K. marginata, K. parviflora, K. pulchra, and K. roscoeana) and six chemical classes (abietanes, labdanes and clerodanes, flavonoids, phenolic compounds, and chalcones) were subjected to principal component analysis (PCA) to identify correlation between different Kaempferia species. In addition, the similarity based on the Pearson correlation coefficient was determined via subjecting the dataset to an agglomerative hierarchical cluster (AHC). The PCA and AHC were performed using an XLSTAT statistical computer software package (version 2018, Addinsoft, NY, USA, www.xlstat.com).

3. Distribution

Zingiberaceae (the ginger family) comprises 52 genera and more than 1300 plant species. Kaempferia is distributed worldwide with diverse members occurring throughout southeast tropical Asian countries such as Indonesia, India, Malaysia, Myanmar, Cambodia, and China, as well as Thailand, including some 60 species [5]. K. pulchra is a perennial herbal plant and widely cultivated in numerous tropical countries, involving Indonesia, Malaysia, Myanmar, and Thailand [12].

4. Traditional Uses

Several Kaempferia species are used widely in folk medicine, including K. parviflora, K. pulchra, and K. galanga (Figure 1). In Laos and Thai, traditional medicines derived from K. parviflora rhizomes are reported for the treatment of inflammation, hypertension, erectile dysfunction, abdominal ailments [6,7], and improvement of the vitality and blood flow [8]. Japanese folk medicine documented a positive effect of K. parviflora extract when used as a food supplement and for the treatment of metabolic disorders [9]. K. pulchra is used extensively as a carminative, diuretic, deodorant, and euglycemic, as well as for the treatment of urinary tract infections, fevers, and coughs [4]. K. galanga is sold as an industrial crop in the market, and its rhizome has been used as a flavor spice of various cooking [13]. The rhizomes of K. galanga is used as an anti-tussive, expectorant, anti-pyretic, diuretic, anabolic, carminative, as well as for curing of gastrointestinal ailments, asthma, wounds, rheumatism, epilepsy, and skin diseases [10]. In Malaysian folk medicines, several gingers belonging to the Zingiberaceae family especially, Kaempheria genus, are used in the treatment of several diseases such as stomach ailments, vomiting, cough, bruises, epilepsy, nausea, rheumatism, sore throat, wounds, eyewash, sore eyes, childbirth, liver complaints, muscular pains, ringworm, asthma, fever, malignancies, swelling, and several other disorders [14].

5. Biological Activity

Extracts and purified compounds of Kaempferia species are used for the treatment of knee osteoarthritis and the inhibition of a breast cancer resistance protein (BCRP), anti-inflammatory, anti-acne, anticholinesterase, anti-obesity-induced dermatopathy, wound healing, anti-drug resistant strains of Mycobacterium tuberculosis, neuroprotective, anti-nociceptive, human immunodeficiency virus type-1 (HIV-1) inhibitory activity, in vitro anti-allergenic, and larvicidal activity against Aedes aegypti [11]. Kaempheria plant extracts and isolated compounds demonstrate numerous and promising biological and pharmaceutical activities, which are summarized in Figure 2.

Figure 2.

Reported biological activities for Kaempheria species.

5.1. Anticancer Activity

Rhizome ethanolic extracts of K. galanga and the purified component ethyl trans p-methoxycinnamate (105) demonstrate moderate cytotoxic activity against human cholangiocarcinoma (CL-6) cells with IC₅₀ of 64.2 and 49.4 μg mL⁻¹, respectively. Significant cholangiocarcinoma (CCA) efficacy as indicated by suppressing tumor growth and lung metastasis in CL6-xenografed mice [15] is also observed. Swapana et al. [16] documented that K. galanga isopimarene diterpenoids, sandaracopimaradiene-9α-ol (2), kaempulchraol I (14), and kaempulchraol L (17) exhibit promising activity against human lung cancer with IC₅₀ of 75 µM, 74 µM, and 76 µM, respectively, and mouth squamous cell carcinoma (HSC-2) inhibition with IC₅₀ of 70 µM, 53 µM, and 58 µM, respectively [16]. The latter compound, isolated from K. pulchra, is reported to have weak anti-proliferative activity against human pancreatic and cervix cancers [17]. Chawengrum et al. [18] stated that K. pulchra labdene diterpenoids, (−)-kolavelool (81), and (−)-2β-hydroxykolavelool (82) exhibit cytotoxic activity against human leukemia cells (HL-60) with IC₅₀ values of 9.0 ± 0.66 and 9.6 ± 0.88 μg mL⁻¹, respectively [18]. Acetone, petroleum ether, chloroform, and MeOH extracts of K. galanga rhizomes show moderate cytotoxicity in a brine shrimp lethality bioassay compared with vincristine sulfate as the reference compound [19]. Moreover, a methanolic extract of K. galanga rhizomes induces Ehrlich ascites carcinoma (EAC) cell death in a dose-dependent manner [20]. 5,7-Dimethoxyflavone (86) isolated from K. galanga was found to reduce cancer resistance to tyrosine kinase inhibitors (TKI) by inhibiting breast cancer resistance protein (BCRP), one of the efflux transporters that increased efflux of TKI out of cancer cells. This was observed both in vitro with a dose-dependent increase in the intracellular concentration of sorafenib in MDCK/BCRP1 breast cancer resistance cells, with an EC₅₀ of 8.78 μM as well as in vivo by increasing sorafenib AUC in mice tissues when co-administered with compound 88, as reported by kinetic results [21]. The isolated methyl-β-D-galactopyranoside specific lectin from the rhizome of K. rotunda exhibited in vitro antitumor activity against Ehrlich ascites carcinoma cells at a pH between 6–9 and a temperature range between 30–80 °C. Tumor inhibition was also observed in vivo in EAC-bearing mice [22].

The cytotoxicity of MeOH, petroleum ether, and EtOAc extracts against C33A cancer cells via MTT and scratch assays compared with essential oils of K. galanga rhizomes showed activity for the EtOAc and MeOH fractions at 1000 μg mL⁻¹ with 11% and 14% cell viability and weak efficacy with petroleum ether extracted essential oils in a MTT assay. Cell growth inhibition was observed with all extracts in the scratch assay [23]. Compound (140) isolated from K. angustifolia was described to have strong activity with an IC₅₀ of 1.4 µg mL⁻¹, which was comparable to 5-fluorouracil as a reference drug. Compound (138) also showed moderate inhibition against human lung cancer. 2′-Hydroxy-4,4′,6′-trimethoxychalcone (flavokawain A; 119) exhibited potent activity against HL-60 and MCF-7 cell lines. The results of Tang et al. [24] revealed that flavokawain A (119) exhibited cytotoxic activity against MCF-7 and HT-29 cell lines with GI₅₀ values of 17.5 µM (5.5 µg mL⁻¹) and 45.3 μM (14.2 µg mL⁻¹), respectively. Kaempfolienol (65) and zeylenol (133) were also found to have moderate activity against HL-60 and MCF-7 cells with IC₅₀ values <30 µg mL⁻¹ and against HL-60 only with an IC₅₀ value of 11.6 µg mL⁻¹ respectively [24].

5.2. Anti-Obesity Activity

An ethanolic extract, a polymethoxyflavonoid-rich fraction (PMF) and a polymethoxyflavonoid-poor fraction from K. parviflora were screened against an obesity-induced dermatopathy system using Tsumura Suzuki obese diabetes (TSOD) mice as an obesity model (Hidaka, Horikawa, Akase, Makihara, Ogami, Tomozawa, Tsubata, Ibuki, and Matsumoto) [11]. The ethanolic extract reduced mouse body weight and the thickness of the subcutaneous fat layer more than the PMF fraction that is used as a dietary supplement in controlling skin disorders caused by obesity [11].

5.3. Anti-HIV Activity

Viral protein R (Vpr) is one of the HIV accessory proteins that can be targeted for controlling viral replication and pathogenesis. A CHCl₃ fraction of K. pulchra exhibits Vpr-inhibitory activity at 25l g mL⁻¹. In addition, isopimarene type diterpenoids isolated from the rhizomes of the plants, kaempulchraol B (43), kaempulchraol D (45), kaempulchraol G (46), kaempulchraol Q (20), kaempulchraol T (36), kaempulchraol U (50), and W (22) inhibit the expression of Vpr at concentrations from 1.56 to 6.25 µM [25].

5.4. Antimicrobial Activity

Arabietatriene (62) isolated from K. roscoeana exhibits antibacterial activity against Gram-positive bacteria Staphylococcus epidermidis and Bacillus cereus [26]. Anticopalic acid (72), anticopalol (77), and 8(17)-labden-15-ol (68) isolated from K. elegans also exhibited antibacterial activity against B. cereus [18]. Acetone, petroleum ether, chloroform, and MeOH extracts of K. galanga rhizomes exhibit moderate antibacterial activity against Gram-positive and Gram-negative bacteria in comparison with ciprofloxacin [19]. Ethyl p-methoxycinnamate (105) also isolated from K. galanga rhizomes have been shown based on a resazurin micro-titer assay to inhibit Mycobacterium tuberculosis H37Ra, H37Rv, multidrug-resistant, and drug-susceptible isolates with MIC 0.242–0.485 mM [27]. Its essential oil also displays strong antibacterial activity against Staphylococcus aureus and Salmonella typhimurium, and weak activity against Escherichia coli [28]. Moreover, essential oils extracted from three varieties of K. galanga exhibited potent larvicidal activity [29]. An ethyl acetate extract of K. rotunda inhibits S. aureus and E. coli [30]. A rhizomes extract of K. galanga inhibits Epstein–Barr virus with no cytotoxic effect in Raji cells [14]. In contrast, isolated diterpenoids from K. roscoeana exhibited no activity against Plasmodium falciparum (Chloroquine-resistant) [26]. Fauziyah et al. [31] described that an ethanolic extract of K. galanga alone exhibits 100% growth inhibition of the multi-drug resistant (MDR) Mycobacterium tuberculosis (isolates at 500 µg mL⁻¹). However, a combination of this extract with streptomycin, ethambutol, and isoniazid showed inhibition values of 55%, 76%, and 50%, respectively. Ethanol, methanol, petroleum ether, chloroform, and aqueous extracts of K. galanga rhizome showed antimicrobial activity against human pathogenic bacteria and fungi, while the ethanolic extract exhibited the strongest inhibition of S. aureus using an inhibition zone assay [32]. However, flavokawain A (119) and other compounds reported from K. angustifolia had no antimicrobial activity against tested microbes [24].

5.5. Antioxidant Activity

The CHCl₃ and MeOH extracts of the rhizomes of K. angustifolia showed strong antioxidant activity against DPPH expressed with 615.92 mg trolox equivalent (TE)/g of extract. In an azinobis (3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS) assay, MeOH extracts showed good antioxidant properties with a value of 38.87 mg TE/g. However, n-hexane extract exhibited significant antioxidant activity with 901.76 mg TE/g in a cupric-reducing antioxidant capacity assay, while EtOAc extract exhibited significant reduction ability against ferric reducing antioxidant power (FRAP) with a value of 342.23 mg TE/g. Also, kaempfolienol (65) showed potent free radical scavenging activity in a DPPH assay, as well as, 2′-hydroxy-4,4′,6′-trimethoxychalcone (119) in ABTS, CUPRAC, and FRAP assays [33,34]. A methanol extract of rhizomes of K. galanga exhibited a concentration-dependent antioxidant activity in DPPH, ABTS, and nitric oxide (NO) radical scavenging assays [20]. Moreover, the essential oil extracts of conventionally propagated and in vitro propagated K. galanga had significant DPPH radical scavenging activity [35]. As well, the ethanol extract of K. rotunda exhibited antioxidant activity in a DPPH assay with IC₅₀ (67.95 μg mL⁻¹) [30].

5.6. Anti-Inflammatory Activity

The cyclohexane, chloroform, and ethyl acetate extracts with diarylheptanoids isolated from K. galanga showed a pronounced inhibition of Lipopolysaccharides (LPS)-induced nitric oxide in macrophage RAW 264.7 cells compared with indomethacin [13]. The EtOH extract and compounds (1, 52, 53, 119, 120) isolated from K. marginata had promising anti-inflammatory activity based on the suppression of NO production and inducible nitric oxide synthase (iNOS) mRNA and cyclooxygenase-2 (COX-2) genes expression [36,37]. Diterpenoids (9–10) isolated from K. pulchra had topical anti-inflammatory activity in 12-O-tetradecanoylphorbol-13-acetate-induced ear edema in rats with ID₅₀ 330 and 50 µg/ear, respectively. Biological activity may be due to the activation of Maxi-K channels in neurons and smooth muscles [38]. The ethanol extract of K. parviflora exhibited potent inhibition of PGE2. The plant extract and 3′,4′,5,7-tetramethoxyflavone (86) were also reported to exhibit a dose-dependent inhibition of iNOS-mRNA expression. Additionally, H₂O, EtOH, EtOAC, CHCl₃, and n-hexane soluble sub-fractions exhibited good in vivo anti-inflammatory activity by decreasing rat paw edema [39]. An 80% EtOH extract reduced UV-induced COX-2 expression in mice skin that was attributed to the anti-oxidative activity of polyphenolics against the oxidizing properties of UV radiation [40]. A 60% EtOH and EtOAc-soluble fraction of 100% methanol extracts of K. parviflora decreased knee osteoarthritis, which was likely due to methoxylated flavones [41]. Ethyl p-methoxycinnamate (105) isolated from K. galana inhibited cytokines as IL-1 and TNFα and endothelial function in rats [42].

Tewtrakul, et al. [43] found that the isolated methoxylated flavonoids from K. parviflora, 5-hydroxy-3,7,3′,4′-tetramethoxyflavone (96), 5-hydroxy-7,4′-dimethoxyflavone (93), and 5-hydroxy-3,7,4′-trimethoxyflavone (95) exhibited anti-inflammatory activity against the PGE₂ production, with IC₅₀ values of 16.1 μM, 24.5 μM, and 30.6 μM, respectively [43]. Tewtrakul and Subhadhirasakul [44] described methoxyflavones 96, 93, and 95 from a hexane extract of K. parviflora rhizomes that exhibited activity against NO release in RAW_264.7 cells with IC₅₀ values of 16.1 μM, 24.5 μM, and 30.6 μM, respectively. In addition, 5-hydroxy-3,7,3′,4′-tetramethoxyflavone (96) inhibited PGE₂ release with an IC₅₀ value of 16.3 μM, with negative activity on Tumor Necrosis Factor alpha (TNF-α) with IC₅₀ >100 μM [44]. Petroleum ether extract from K. galanga was active against acute inflammation at 300 mg/kg in rats and inhibited the inflammation and MPO levels at 100 mg kg⁻¹ in the chronic model [45].

5.7. Anticholinesterase Activity

According to Sawasdee et al. [46], a MeOH extract as well as compounds (86–87) isolated from K. parviflora rhizomes inhibited acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with greater cholinesterase inhibitory toward AChE and BChE for (86), which was an observation of significance in the treatment of Alzheimer’s disease [46].

5.8. Anti-Mutagenicity Activity

CH₂Cl₂ and EtOAc soluble fractions of K. parviflora showed anti-mutagenicity and α-glucosidase inhibitory activity. Isolated methoxylated compounds (86, 97, 84, and 92) from these extracts exhibited potent activity with IC₅₀ values of 0.40, 0.40, 0.42, and 0.47 nmol/plate, respectively. Compounds (88, 87, and 91), also showed significant activity with IC₅₀ values of 20.4 μM, 54.3 μM, and 64.3 μM, respectively [47].

5.9. Effect on Cytochromes CYP 450

The results listed by Ochiai et al. [48] stated that the continued ingestion of (88) isolated from K. parviflora decreases liver CYP3A expression, which in turn increased levels of compounds metabolized by CYP3As such as midazolam [48].

5.10. Vascular Activity

The oral administration of CH₂Cl₂ extract of K. parviflora in middle-aged rats was found to decrease vascular responses to phenylephrine, increase acetylcholine-induced vasorelaxation and the production of nitric oxide (NO) from blood vessels, and decrease visceral, subcutaneous fat, fasting serum glucose, triglyceride, and liver lipid accumulation [49]. The effect of intravenous administration of a CH₂Cl₂ extract of K. galanga to rats reduced the mean arterial blood pressure [50]. This anti-hypertensive effect was attributed to ethyl cinnamate, which is a major compound in the extract [50]. The ethanol extract of rhizomes of K. parviflora caused dose-dependent relaxation on aortic rings as well as ileum pre-contracted with phenylephrine and acethylcholine [51].

5.11. Adaptogenic Activity

Hexane, chloroform, methanol, and ethanol extracts of K. parviflora exhibited adaptogenic activity compared with a crude ginseng root powder used as a reference [52]. A single oral dose of K. parviflora rhizome (60% EtOH extract) increased the whole-body potential expenditure in humans [53]. K. parviflora was also found to improvement physical fitness and health by decreasing oxidative stress [54].

5.12. Xanthine Oxidase Inhibitory Activity

Among the isolated methoxylated flavonoids from K. parviflora, (87 and 86) inhibit xanthine oxidase activity with IC₅₀ values of 0.9 and >4 mM, respectively [9].

5.13. Allergenic Activity

Isolated polymethoxyflavones from K. parviflora (86, 97), in addition to CH₂Cl₂, EtOAc, and H₂O extracts, alleviated type I allergy symptoms through suppressing Rat Basophilic Leukemia cells (RBL-2H3) cell degranulation, with (92) and (94) showing the highest anti-allergenic activity [55].

5.14. Neurological Activity

A methanolic extract (95% MeOH) of K. parviflora exhibited neuroprotective activity by increasing rat hippocampus serotonin, norepinephrine, and dopamine levels in comparison with a vehicle-treated group [56]. An acetone extract of K. galanga rhizomes and leaves also exhibited central nervous system depressant activity [57].

5.15. Nociceptive Activity.

A K. galanga rhizome extract exhibited anti-nociceptive activity in rats that was stronger than aspirin but weaker than morphine. The efficacy was abolished by naloxone, suggesting that the analgesic effect may be centrally and peripherally mediated [58].

5.16. Wound-Healing Activity

The co-administration of a K. galanga rhizomes extract (95% EtOH) with dexamethazone was found to have wound-healing activity in mice comparable to dexamethazone only [59].

5.17. Effects on Sexual Performance

Several 7-methoxyflavones (86, 87, 89, 91, 93–95) isolated from K. parviflora rhizomes improved sexual activity in males through the inhibition of PDE5, with 86 being the most potent [60]. The activity was attributed to methoxyls present at positions C5 and C7 [60]. K. parviflora rhizome extracts, standardized to 5% DMF, also improve erectile function in healthy men [61]. A K. parviflora extract as well as 5,7-dimethoxyflavones augment testosterone production, which decreases age-related diseases and hypogonadism [62]. Improved testosterone levels, sperm count, and sexual performance was observed in streptozotocin (STZ)-induced diabetic rats when treated with a K. parviflora extract (aqueous with 1% Tween-80) [63].

5.18. Miscellaneous

The rhizome extract (95% ethanolic) of K. parviflora reduced obesity via the inhibition of adipogenesis, lipogenesis, and muscle atrophy in mice [64]. In contrast, the K. parviflora derivatives of 5-hydroxy-7-methoxyflavone induce skeletal muscle hypertrophy [65]. A K. parviflora extract (95% EtOH) served as a potential anti-acne agent with anti-inflammatory, sebostatic, and anti-propioni bacteria activity [66].

Recently, K. parviflora alcoholic extract at 3–30 µg mL⁻¹ was evaluated regarding the molecular mechanisms associated with rheumatoid arthritis for up to 72 h compared with the dexamethasone as positive control [67]. They documented that the EtOH extract significantly decreased the gene expression levels of pro-inflammatory cytokines, inflammatory mediators, and matrix-degraded enzymes, but neither induced apoptosis nor altered the cell cycle. They also reported that the alcoholic extract inhibits cell migration, reduces the mRNA expression of cadherin-11, and selectively reduces the phosphorylation of mitogen-activated protein kinases (P38, MAPKs), signal transducers, and activators of transcription 1 (STAT1) and 3 (STAT3) signaling molecules, without interfering with the NF-κB pathway [67].

A K. galanga extract (acetone, petroleum ether, chloroform, or methanolic) exhibited dose-dependent anthelmintic activity with strong paralytic activity within one hour and death within 80 min at a 25 mg mL⁻¹ concentration [68].

6. Chemical Metabolites of Kaempferia Species

Chemical profiles of Kaempferia exhibited the presence of different types of secondary metabolites such as terpenoids, especially isopimarane phenolic compounds, diarylheptanoids [13], flavonoids [69,70,71], and essential oils [72,73]. This review summarized the reported variety of compound types, including isopimarane, abietane, labdan, and clerodane diterpenoids, flavonoids, phenolic acids, phenyl-heptanoids, curcuminoids, tetrahydropyrano-phenolic, and steroids. Diterpenoids, especially isopimarane types, were the most reported compounds from the plants of this genus, in addition to phenolics, flavonoids, and essential oils. Each class will be described and listed in the following items, and the structures will be summarized in Table 1, Table 2 and Table 3.

Table 1.

Diterpenoids.

No	Name	R	R1	R2	R3	R4	R5	R6	R7	Plant	Ref
1	Sandaracopimaradiene	H	H	H	H	H	H	H	H	K. galanga K. roscoeana K. marginata	[4,16,17,25,26,36,74,75,76]
2	Sandaracopimaradiene-9α-ol	α-OH	H	H	H	H	H	H	H
3	8(14),15-Sandaracopimaradiene-1α,9α-diol	α-OH	H	α-OH	H	H	H	H	H	K. galanga K. pulchra K. sp.
4	1,11-Dihydroxypimara-8(14),15-diene	H	H	α-OH	H	H	α-OH	H	H
5	6β-Hydroxypimara-8(14),15-diene-1-one	H	β-OH	=O	H	H	H	H	H	K. galanga K. marginata
6	Sandaracopimaradien-6β,9α-diol-l-one	α-OH	β-OH	=O	H	H	H	H	H	K. galanga
7	Boesenberol I	α-OH	H	=O	H	H	H	α-OH	H
8	Boesenberol J	α-OH	β-OH	=O	H	H	H	H	H	K. galanga
9	Sandaracopimaradien-1α,2α-diol	H	H	α-OH	α-OH	H	H	H	H	K. roscoeana K. pulchra K. marginata	[26,38,75]
10	2α-Acetoxy-sandaracopimaradien-1α-ol	H	H	α-OH	α-OAc	H	H	H	H	K. pulchra K. marginata
11	Kaempulchraol E	α-H	β-OH	α-OH	H	H	H	H	H	K. galanga K. pulchra
12	Kaempulchraol F	H	H	α-OH	H	α-OH	H	H	H	K. pulchra	[4,16,17,25,26,74]
13	Kaempulchraol H	H	β-OH	α-OH	H	α-OH	H	H	H
14	Kaempulchraol I	H	H	α-OH	H	H	H	H	H	K. galanga K. pulchra K. roscoeana
15	Kaempulchraol J	H	H	α-OH	H	H	H	=O		K. pulchra
16	Kaempulchraol K	α-OH	β-OAc	H	H	H	H	H	H
17	Kaempulchraol L	α-OMe	β-OH	H	H	H	H	H	H	K. galanga K. pulchra
18	Kaempulchraol M	α-OH	H	α-OH	α-OH	H	H	H	H	K. pulchra
19	Kaempulchraol P	H	β-OH	H	H	H	H	H	H
20	Kaempulchraol Q	α-OAc	β-OH	H	H	H	H	H	H
21	Kaempulchraol R	α-OH	H	H	H	H	H	α-OAc	H
22	Kaempulchraol T	H	β-OH	H	H	H	H	α-OAc	H
23	Kaempulchraol V	α-OH	β-OH	H	H	H	H	β-OAc	H
24	Kaempulchraol W	α-OH	β-OH	H	H	H	H	β-OH	H
25	9 α-Hydroxyisopimara-8(14),15-dien-7-one	α-OH	H	H	H	H	H	=O	H
26	7β,9 α-Dihydroxypimara-8(14),15-diene	α-OH	H	H	H	H	H	β-OH	H
27	Isopimara-8(14),15-dien-7-one	H	H	H	H	H	H	=O	H	K. roscoeana	[26]
28	(1S,5S,9S,10S,11R,13R)-1,11-Dihydroxypimara-8(14),15-diene	H	H	α-OH	H	H	α-OH	H	H	K. roscoeana K. marginata K. pulchra	[4,17,25,26,74,75]
29	(1R,2S,5S,9S,10S,11R,13R)-1,2,11-Trihydroxypimara-8(14),15-diene	H	H	α-OH	α-OH	H	α-OH	H	H
30	7α-Hydroxyisopimara-8(14),15-diene	H	H	H	H	H	H	α-OH	H	K. roscoeana K. pulchra
31	Sandaracopimaradien- 9α-ol-l-one	α-OH	H	=O	H	H	H	H	H	K. sp	[76]
32	6β-Acetoxysandaracopimaradien-9α-ol-l-one	α-OH	β-OAc	=O	H	H	H	H	H
33	Sandaracopimaradien-6β,9α-diol-l-one	α-OH	β-OH	=O	H	H	H	H	H
34	6β-Acetoxysandaracopimaradien-lα,9α-diol	α-OH	β-OAc	α-OH	H	H	H	H	H
35	Sandaracopimaradien- lα,6β,9α-triol	α-OH	β-OH	α-OH	H	H	H	H	H
36	Roscorane B	H	H	H	H	H	α-OH	H	OH	K. roscoeana	[26]
37	Roscorane C	H	β-OH	H	OH	H	H	OH	H
38	Roscorane D	H	H	H	OH	H	H	OH	OH
39	(1R,2S,5S,7S,9R,10S,13R)-1,2,7-Trihydroxypimara-8(14),15-diene	H	H	H	α-OH	H	H	β-OH	H	K. marginata	[75]
40	(1S,5S,7R,9R,10S,11R,13R)-1,7,11-Trihydroxypimara-8(14),15-diene	H	β-OH	H	H	H	H	α-OH	H
41	(1R,2S,5S,7S,9R,10S,13R)-1,2-Dihydroxypimara-8(14),15diene-7-one	H	H	H	α-OH	H	H	H	H
52–54						42–51
No	Name		R1	R2			R3	R4	Plant		Ref
42	Kaempulchraol A		H	β-OH			H	α-OMe	K. pulchra		[4,17,25,74]
43	Kaempulchraol B		H	β-OH			H	β-OMe
44	Kaempulchraol C		H	β-OH			H	α-OH
45	Kaempulchraol D		H	β-OH			H	β-OH
46	Kaempulchraol G		H	β-OH			H	=O
47	Kaempulchraol N		α-OH	β-OH			H	α-OH
48	Kaempulchraol O		α-OH	β-OH			H	β-OMe
49	Kaempulchraol S		H	H			=O	α-OH
50	Kaempulchraol U		H	H			H	α-OH
51	Isopimara-8(9),15-dien-7-one		H	H			=O	H	K. roscoeana		[26]
52	8(14),15-Isopimaradiene-6α-ol		H	α-OH			H	---	K. marginata		[36]
53	1α-Acetoxy-sandaracopimaradiene		α-OAc	H			H	-
54	1α-Acetoxy-sandaraco pimaradien-2-one		α-OAc	=O			H	-
No	Name		Structure				Plant				Ref
55	(2R)-ent-2-Hydroxyisopimara-8(14),15-diene						K. pulchra				[4,17,25,74]
56	Kaemgalangol A						K. galanga				[16]
57	Roscorane A						K. roscoeana				[26]
58	R=OMe; Roscotane A						K. roscoeana				[26]
59	R=H; Roscotane B
60	Roscotane C
61	Roscotane D
62	R=H; Ar-abietatriene
63	R=[=O]; 7-Dehydroabietanone
64	R=α-OH; Abieta-8,11,13-trien-7α-ol
65	Kaempfolienol						K. angustifolia				[33,34]
66	(12Z,14R)-Labda-8(17),12-dien-14,15,16-triol						K. roscoeana				[26]
67	Propadane A						K. elegans				[18]
68	R=H --- 8(17)-Labden-15-ol
69	R=OH; Propadane B
70	Propadane C						K. pulchra
71	Cleroda-2,4(18),14-trien-13-ol						K. pulchra
72	R=H; Anticopalic acid						K. elegans
73	R=Me; Methyl anticopalate
74	(+)-15,16-Eoxy-8(17),13(16),14-labdatriene										[18]
75	(+)-Pumiloxide
76	13-Oxo-14,15-bis-nor-labd-8(17)-ene
77	Anticopalol						K. elegans
78	Labda-8(17),13(14)-diene-15,16-olide
79	(+)-Labda-8(17),13(Z)-diene-15,16-diol
80	Calcaratarin A						K. pulchra
81	R=H; (-)-Kolavelool										[18]
82	R= β-OH; (-)-2β-Hydroxykolavelool
83	R=β-OMe; Dysoxydensin E
84	13-Epi-roseostachenone
85	(+)-13-Epi-2α-hydroxykolavelool (13-epi-roseostachenol)						K. pulchra

Table 2.

Flavonoids and phenolics (Flavonoids).

86–97		98–101				102–103
No	Name	R1	R2	R3	R4	Plant	Ref
86	5,7-Dimethoxyflavone	H	Me	H	H	K. parviflora	[9,55,71,77]
87	4‘,5,7-Trimethoxyflavone	H	Me	H	OMe
88	3‘,4‘,5,7-Tetramethoxyflavone	H	Me	OMe	OMe
89	3,5,7-Trimethoxyflavone	OMe	Me	H	H
90	3,5,7,4‘-Tetramethoxyflavone	OMe	Me	H	OMe
91	3,5,7,3‘,4‘-Pentamethoxyflavone	OMe	Me	OMe	OMe
92	5-Hydroxy-7-methoxyflavone	H	H	H	H
93	5-hydroxy-7,4‘-dimethoxyflavone	H	H	H	OMe
94	5-Hydroxy-3,7-dimethoxyflavone	OMe	H	H	H
95	5-Hydroxy-3,7,4‘-trimethoxyflavone	OMe	H	H	OMe
96	5-Hydroxy-3,7,3‘,4‘-tetramethoxy flavone	OMe	H	OMe	OMe
97	5,3‘-Dihydroxy-3,7,4‘-trimethoxyflavone	OMe	H	OH	OMe
98	Kaempferol	H	OH	-	-	K. galanga	[42]
99	Kaempferide	H	OMe	-
100	Tectochrysin	Me	H	-	-	K. parviflora
101	Genkwanin	Me	OH	-	-		[46]
102	Pinocembin	H	-	-	-	K. parviflora K. angustifolia	[71]
103	Pinostrobin	Me	-	-	-
104	Sakuranetin
105	2″,2″-Dimethylpyrano-[5″,6″:8,7]-flavone					K. pulchra	[18]
106–109		110–113				114–115
116–117			118–119
No	Name	R1	R2		R3	Plant	Ref
106	Ethyl trans-p-methoxycinnamate	H	OMe		CH2Me	K. galanga	[13]
107	Ferulic acid	OMe	OH		H
108	trans-p-Hydroxy-cinnamic acid	H	OH		H
109	trans-p-Methoxy cinnamic acid	H	H		CH2Me
110	p-Hydroxybenzoic acid	H	OH		COOH		[13,50]
111	p-Methoxybenzoic acid	H	OMe		COOH
112	Vanillic acid	OMe	OH		COOH
113	Methyl 3,4-dihydroxybenzoate	OH	OH		COOMe
114	Methyl (2R,3S)-2,3-dihydroxy-3-(4-methoxyphenyl) propanoate	Me	-		-
115	Ethyl-(2R,3S)-2,3-dihydroxy-3-(4-methoxyphenyl) propanoate	CH2Me	-		-
116	(1R,3R,5R)-1,5-Epoxy-3-hydroxy-1-(3,4-dihydroxyphenyl)-7-(3,4-dihydroxy phenyl) heptane	H	-		-		[13]
117	(1R,3R,5R)-1,5-Epoxy-3-hydroxy-1-(3,4-dihydroxyphenyl)-7-(4-hydroxyphenyl) heptane 3-O-β-D-glucopyranoside	D-glc	-		-
118	2‘-hydroxy-4‘,6‘-dimethoxychalcone	H	-		-	K. parviflora K. angustifolia	[24,71]
119	2‘-hydroxy-4,4‘,6‘-trimethoxychalcone	Me	-		-
No	Name	Structure				Plant	Ref
120	Desmethoxyyangonin					K. marginata	[36]
121	Bisdemethoxycurcumin
122	1-(4-Hydroxy-3-methoxyphenyl)-7-(4-hydroxyphenyl)heptane-1,2,3,5,6-pentaol					K. galanga	[13]
123	(3R,5S)-3,5-Dihydroxy-1-(3,4-dihydroxyphenyl)-7-(4-hydroxy phenyl) heptane					K. galanga
124	Phaeoheptanoxide
125	Hedycoropyran B
126	1-O-4-Carbonxylphenyl-(6-O-4-hydroxybenzoyl)-β-D-glucopyranoside
127	Dihydro-5,6-dehydrokawain					K. parviflora	[13,50]
128	R=OH; (-)-Hydroxypanduratin A
129,	R=OMe; (-)-Panduratin A
130	Cinnamaldehyde					K. galanga	[78]
131	R=Me; Crotepoxide					K. angustifolia	[24,33]
132	R=Benzen; Boesenboxide
133 134	R=H; Zeylenol R=Me; 6-methylzeylenol
135	rel-(5aS,10bS)-5a,10b-Dihydro-1,3,5a,9-tetrahydroxy-8-methoxy-6H-benz[b]indeno[1–d]furan-6-one 5a-O-[α-l-rhamnopyranosyl-(1→6)-β-d-glucopyranoside]	R=α-L-rha-(1→6)-β-D-glc				K. parviflora	[79]
136	rel-(5aS,10bR)-5a,10b-Dihydro-1,3,5a,9-tetrahydroxy-8-methoxy-6H-benz[b]indeno[1–d]furan-6-one 5a-O-[α-l-rhamnopyranosyl-(1→6)-β-d-glucopyranoside]	R=α-L-rha-(1→6)-β-D-glc
137	(2R,3S,4S)-3-O-[α-l-Rhamnopyranosyl-(1 → 6)-β-d-glucopyranosyl]-3′-O-methyl-ent-epicatechin-(2α→O→3,4α→ 4)-(5aS,10bS)-5a,10b-dihydro-1,3,5a,9-tetrahydroxy-8-methoxy-6H-benz[b]indeno[1,2-d]furan-6-one 5a-O-[α-l-rhamnopyranosyl-(1→ 6)-β-d-glucopyranoside]	R=α-L-rha-(1→6)-β-D-glc

Table 3.

Steroid and triterpenes.

138–139
No	Name	Structure	Plant	Ref
138	β-Sitosterol	R=H	K.marginata K. angustifolia	[24,33,36]
139	β-Sitosterol-β-D-glucoside	R=β-D-glc
140	Stigmasterol
141	(24S)-24-methyl-lanosta-9(11), 25-dien-3β-ol		K. angustifolia	[24]

6.1. Diterpenoids

Kaempferia plants were characterized with a predominance of diterpenoids, especially the isopimaranes in addition to abietane, labdane, and clerodane types (Table 1).

6.1.1. Isopimarane-Type Diterpenoids

The isopimaranes reported from the Kaempheria species (Table 1) are characterized with the presence of two double bonds; one is mostly ∆¹⁵⁽¹⁶⁾, while the other is between ∆⁸⁽⁹⁾ or ∆⁸⁽¹⁴⁾ [4,25,74]. From the rhizomes of K. galanga, 12 usual isopimarenes (1–8, 10, 11, 14, and 17) were observed that contained a ∆^8(14),15 motif in addition to the rarely reported oxygenated seco-isopimarane (56) [16]. From the rhizomes of K. marginata, five isopimarenes with a ∆^8(14),15 motif were observed (1, 2, 52–54) [36]. Only one thumbing isopimarenes, roscorane A (57), was reported from K. roscoeana, which was characterized by only one double bond ∆⁸⁽⁹⁾ and (7-8)-epoxy, as well as the absence of the exomethylene ∆¹⁵⁽¹⁶⁾ [26].

Biosynthesis of Isopimarane-Type Diterpenoids

Isopimarane diterpenoids are the most characteristic compounds for Kaempheria plants. (E,E,E)-Geranylgeranyl diphosphate (GGPP) is a well-known biosynthesized intermediate of diterpenoids as described by [80]. GGPP is firstly cyclized via copalyl diphosphate (CPP) synthases (CPS), and then by the unknown enzyme (PS), affording a charged intermediate (INM). Then, this intermediate is completely cyclized by the enzymatic reactions via the bifunctional (iso) pimaradiene synthases (AoCPS-PS, NfCPS-PS, and AfCPS-PS) (Scheme 1), as described by Xu et al. [81].

Scheme 1.

Plausible isopimaradiene biosynthesis [81] starting with (E,E,E)-geranylgeranyl diphosphate (GGPP): (E,E,E)-geranylgeranyl diphosphate; CPS: copalyl diphosphate (CPP) synthases; PS: Unknown enzyme; AoCPS-PS, NfCPS-PS, and AfCPS-PS: bifunctional (iso) pimaradiene synthases.

6.1.2. Abietane-Type Diterpenoids

Seven abietanes (58–64) (Table 1) have been isolated and characterized from the rhizomes of K. roscoeana, and one (65) was isolated and characterized from K. angustifolia [26,33,34]. These highly oxygenated metabolites contain one or more double bonds and an absence of exomethylenes, except for roscotane D (61), which contains no double bonds.

6.1.3. Labdane and Clerodane Diterpenoids

After isopimarenes, labdane and clerodane represent major diterpenoid classes from the Kaempheria species. Nineteen highly oxygenated labdanes and clerodanes (66–86) have been reported from Kaempheria rhizomes (Table 1) [18,26]. From these isolated labdanes, only (12Z,14R)-labda-8(17),12-dien-14,15,16-triol (66) has been isolated from K. roscoeana rhizomes. In contrast, several labdane and clerodane types of diterpenoids have been isolated from K. elegans and K. pulchra rhizomes collected in Thailand.

6.1.4. Flavonoids

Kaempheria species are characterized by rich biological activity due in part to the presence of a diversity of flavonoids (86–105) and phenolic compounds (106–137) (Table 2). K. parviflora rhizomes with flavonoid nuclei contain methoxy groups in specific positions (86–97) [9,55]. Pyrano-flavone, 2”,2”-dimethylpyrano-[5”,6”:8,7]-flavone (105), has been isolated from K. pulchra rhizomes collected from Thailand [18], and flavanones (97–99) have been isolated and identified from K. parviflora rhizomes [70,71]. K. galanga contains kaempferol and kaempferide (98, 99) [78].

6.1.5. Phenolic Compounds

From K. galanga rhizomes, diarylheptanoid compounds (116, 117, 122–125) are reported by Yao, Huang, Wang, and He [13]. From K. marginata rhizomes, curcuminoid (121) was characterized by Kaewkroek, Wattanapiromsakul, Kongsaeree, and Tewtrakul [36]. From K. galanga, rhizomes phenolic acids (106–113) were the major compounds isolated, including methoxylated cinnamic acid derivatives. Two (4-methoxyphenyl)-propanoates (114–115) were also isolated from the K. galanga rhizomes [13,50]. S- and R-isomers at C-4 of phenolic glycosides (135 and 136) as well as a rare phenolic glycoside (137) were observed in K. previflora rhizomes [79]. All the phenolic compounds (106–137) are summarized in Table 2.

6.1.6. Steroids and Triterpenes

Steroids represent a minor class of compounds reported from Kaempheria species. Only three steroids, β-sitosterol (138), β-sitosterol-β-D-glucoside (139), and stigmasterol (140) (Table 3) have been reported from K. marginata rhizomes [36]. Moreover, only one lanostane type triterpene, (24S)-24-methyl-lanosta-9(11), 25-dien-3β-ol (141), was isolated from K. angustifolia [24].

6.1.7. Volatile Oils

Kaempheria species were documented as very rich plants with volatile oils such as K. galanga [29,73,82,83], K. angustiflora [29], and K. marginata [29]. The volatile oil of K. galanga has been reported as a potential market product in India and over all the world with market values around 600–700 US$/kg on the international market [83]. Phenylpropanoids and/or cinamates were represented as major constituents of volatile oils derived from Kaempheria species followed by monoterpenes [29,73,82]. The phenylpropanoid compound, trans-ethyl cinnamate, was documented as a principal component of volatile oils of all the studied Kaempheria species up to date with concentrations varied from 16–35% of the total identified [29,73,82,83]. The volatile oils of Kaempheria species were reported to have numerous biological activities such as anti-microbial [83], antioxidant [35], nutraceutical [83], nematicidal toxicity [82], and larvicide activities [29]. Table 4 summarized the main components (142–157) of the reported volatile oils of Kaempheria species.

Table 4.

Main components of volatile oils of Kaempferia species.

No	Name	Plant	Ref
142	δ-3-Carene	K. galanga	[29,35,82,83]
143	E-Ethyl cinnamate
144	Ethyl-p-methoxycinnamate
145	γ-Cadinene
146	1,8-Cineole
147	Trans-cinnamaldehyde
148	Borneol
149	Pentadecane
150	γ-car-3-ene
151	Linoleoyl chloride
152	Caryophyllene oxide
153	Cubenol
154	Caryophyllene
155	Limonene
156	Camphene
157	α-Pinene

7. Principal Components Analysis (PCA) and Agglomerative Hierarchical Clustering (AHC) for Kaempferia Species

To assess the correlation between the various Kaempferia species, chemical classes of different compounds were subjected to PCA and AHC (Figure 3). According to the similarity, the analysis showed that we can group the Kaempferia species under three groups: the first group comprised K. galanga, K. marginata, K. pulchra, and K. roscoeana, and these species are correlated to isopimaranes compounds. The Pearson correlation coefficient (r) between K. marginata and K. pulchra was the highest with r = 0.938, while between K. marginata and K. roscoeana, it was 0.771, between K. roscoeana and K. pulchra, it was 0.766, and between K. marginata and K. galanga, it was 0.615 (Table 5).

Figure 3.

(A) Agglomerative hierarchical clustering (AHC) and (B) Principal component analysis (PCA) based on the chemical composition of different chemical classes of seven Kaempferia species (K. angustifolia, K. elegans, K. galanga, K. marginata, K. parviflora, K. pulchra, and K. roscoeana).

Table 5.

Proximity matrix (Pearson correlation coefficient) of the seven Kaempferia species based on the chemical classes reported.

	K. angustifolia	K. elegans	K. galanga	K. marginata	K. parviflora	K. pulchra
K. elegans	−0.539
K. galanga	−0.042	−0.339
K. marginata	−0.500	−0.241	0.615
K. parviflora	0.833	−0.312	0.075	−0.280
K. pulchra	−0.675	0.053	0.378	0.938	−0.372
K. roscoeana	−0.643	−0.225	0.206	0.771	−0.513	0.766

The second group contained K. angustifolia and K. parviflora (r = 0.833), and this group showed a close correlation to flavonoids and phenolics. However, the K. elegans was separated alone, and showed a close relation to labdane and clerodane compounds. The similarities within each group might be ascribed to the genetic relations, as well as the environmental and microclimatic conditions [1,2,3].

In a study of a genetic variation of Kaempferia species based on chloroplast DNA [5], K. marginata and K. galanga were grouped together, which is agreeable with our results (r = 0.615) according to the PCA data of the present study based on the chemical composition. However, in contrast to the data from the PCA, K. angustifolia and K. parviflora were separated in different groups, but K. elegans and K. parviflora were grouped together. In another recent study, based on the DNA and morphological characteristics [84], K. angustifolia and K. parviflora were grouped together in agreement with the chemical variation of the present study.

8. Conclusions

Kaempheria species are widely used plants in traditional medicine worldwide. All the biological activity data for these plants and their isolated constituents have resulted in numerous leads for medicinal drugs. Mainly, seven rhizomes of Kaempheria plants afforded a vast array of diterpenoids, especially the isopimarane type, along with significant bioactive methoxylated flavonoids. From all these documented chemical and biological results, these plants have been and continue to be a promising source for medicinal natural products and food industrial products.

Abbreviations

K.	Kaempheria
Sp.	Species
PCA	Principal component analysis
AHC	Agglomerative hierarchical clustering
CCA	Significant Cholangiocarcinoma
HSC-2	Mouth squamous cell carcinoma
EAC	Ehrlich ascites carcinoma cancer cells
HL-60	Human leukemia cancer cells
CL-6	Human cholangiocarcinoma cells
TKI	Tyrosine kinase inhibitors
BCRP	Breast cancer resistance protein
MTT	(3-[4,5,[4,5-Dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide) assay
CH2Cl2	Dichloromethane
BChE	Butyrylcholinesterase
NO	Nitric oxide
CUPRAC	Modified cupric reducing antioxidant capacity
PDE5	Phosphodiesterase type 5 inhibitor
AP	Aerial parts
AChE	Acetylcholinesterase
RBL-2H3	Rat Basophilic Leukemia cells
P38	Type of mitogen-activated protein kinases
STAT1 and 3	Signal transducers and activators of transcription 1 and 3
MeOH	Methanol
EtOAc	Ethyl acetate
MCF-7	Breast cancer cells
HT-29	Colorectal adenocarcinoma cell
PMF	Polymethoxyflavonoid-rich fraction
TSOD	Tsumura Suzuki obese diabetes
GGPP	(E,E,E)-Geranylgeranyl diphosphate
CPP	Copalyl diphosphate
CPS	Copalyl diphosphate synthases
EtOH	Ethanol
AChE	Acetylcholinesterase
ABTS	2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) assay
Vpr	Viral protein R
DPPH	1,1-Diphenyl-2-picrylhydrazyl assay
FRAP	Ferric reducing antioxidant power
CYP3A	Cytochrome P450, family 3, subfamily A
NF-κB	Nuclear factor pathway
Rh	Rhizomes
BChE	Butyrylcholinesterase
STZ	Streptozotocin
MPO	myeloperoxidase
DMF	Dimethylformamide
MAPKs	Type of mitogen-activated protein kinases
PGE2	Prostaglandin E2

Author Contributions

A.I.E., T.A.M. and M.-E.F.H. suggested and designed the study. A.I.E., T.A.M., A.F.E., and A.M.A.-E.G. did the data preparation and structure drawing. A.I.E., T.A.M., A.M.A.-E.G., and M.-E.F.H. collected the data. A.S.A., A.A.S., T.Y., A.R.H.F., and M.N. wrote the original manuscript. A.I.E., T.A.M., M.-E.F.H., P.W.P., A.U., A.S.A., A.A.S., and H.R.E.-S. edited the final manuscript. All the authors reviewed and approved the manuscript.

Funding

This research received no external funding.

Conflicts of Interest

The authors declare no conflict of interest.