An Overview on Cardamonin

Abstract

Cardamonin, as shown by the increasing number of publications, has received growing attention from the scientific community due to the expectations toward its benefits to human health. In this study, research on cardamonin is reviewed, including its natural sources, health promoting aspects, and analytical methods for its determination. Therefore, this article hopes to aid current and future researchers on the search for reliable answers concerning cardamonin's value in medicine.

Introduction

In the last decades, a lot of efforts have been dedicated to research on chalcones. This group of aromatic enones (1,3-diphenyl-2-propenone core structure) belongs to the flavonoid family and is often responsible for the yellow pigmentation of plants.^1–3 In fact, the name chalcones comes from the classic Greek word chalkos, “χαλκóς,” which means copper/bronze. However, and of course, the scientific community's interest is beyond a matter of color and mostly aims at the promising cancer chemopreventive properties as well as other remarkable bioactive characteristics like the antioxidant and antibacterial potential.⁴ Moreover, they have the inherent advantage of occurring naturally, often in plants already present in our diet,⁵ thus simplifying the process of having these compounds approved within developed pharmaceutical formulations.

Several chalcones have been subject of interest in medicinal chemistry⁴ like hesperidin methyl-chalcone (already tested in clinical trials),⁶ xanthohumol,^7–10 licochalcone A,¹¹ flavokawin,¹² and xanthoangelol.¹³ In the authors' opinion, cardamonin (Fig. 1) can be included in this list as can be seen by the increasing number of publications (Fig. 2).

FIG. 1.

Cardamonin structure.

FIG. 2.

Number of published documents per period of time. Source: SciFinder search engine, all publications concerning cardamonin, that is, CAS registry number 1939-14-9.

This article attempts to overview all the work published so far considering the health promoting properties of cardamonin, all plant sources, and finally, a list of all analytical methodologies that have been developed.

Sources Of Cardamonin

Although chalcones were first synthetized in the laboratory in the end of the XIX century,³ it is still a topic of research nowadays. In general, they are synthetized by acid or base catalyzed Claisen-Schmidt condensation (Fig. 3A) of an aldehyde and a ketone followed by dehydration.^2,14–16 There are also articles based on the Suzuki reaction^17,18 and an interesting example of chalcone synthesis (including cardamonin) that can be found in literature using a bromomagnesium salt.¹⁹

FIG. 3.

General scheme for chalcone synthesis: (A) chemical synthesis, (B) simplified biosynthesis of hydroxylated chalcone.

Of course, naturally occurring synthesis is chemically more complex and involves several enzymes.^3,20 The initial product is phenylalanine transformed to cinnamic acid by phenyl ammonium-lyase (EC 4.3.1.24), and then, in several steps where malonyl-CoA plays a major role, a hydroxylated chalcone is obtained (Fig. 3B); quite commonly, the chalcone can be transformed into the corresponding flavanone by a chalcone isomerase.²¹

The first isolation of naturally occurring chalcones was done in 1910.³ Chalcones are mainly found in the petal pigments, but have been found as well in the heartwood, bark, leaf, fruit, and root of many plant species.³

Cardamonin's name comes from the fact that it can be found in cardamom spice (Fig. 4), but since the first article where it was described,²² it has been found in many other (some of them edible) plant species, such as Alpinia blepharocalyx,^23,24 Alpinia gagnepainii,²⁵ Alpinia conchigera,^26,27 Alpinia hainanensis,^28–40 Alpinia malaccensis,⁴¹ Alpinia mutica,^42,43 Alpinia pricei,⁴⁴ Alpinia rafflesiana,^45–48 Alpinia speciosa,^22,49,50 Amomum subulatum,⁵¹ Artemisia absinthium,⁵² Boesenbergia pandurata,^53–60 Boesenbergia rotunda,^61,62 Carya cathayensis,⁶³ Cedrelopsis grevei,⁶⁴ Combretum apiculatum,⁶⁵ Comptonia peregrina,⁶⁶ Desmos cochinchinensis,⁶⁷ Elettaria cardamomum,⁶⁸ Helichrysum forskahlii,⁶⁹ Kaempferia parviflora,⁵⁴ Morella pensylvanica,⁶⁶ Piper dilatatum,⁷⁰ Piper hispidum,⁷¹ Polygonum ferrugineum,⁷² Polygonum lapathifolium,⁷³ Polygonum persicaria,^74,75 Populus fremontii,⁷⁶ Populus×euramericana, a hybrid between Populus deltoides and Populus nigra,⁷⁷ Syzygium samarangense,⁷⁸ Vitex leptobotrys,⁷⁹ and Woodsia scopulina.⁸⁰

FIG. 4.

Photograph of green cardamom seeds by Luc Viatour (www.lucnix.be). Color images available online at www.liebertpub.com/jmf

Table 1 shows the taxonomic position of all species by the Integrated Taxonomic Information System (ITIS; www.itis.gov/, http://eol.org/). Some data immediately strike out like the fact that not only cardamonin can be found in many different species, but also they are taxonomically very much apart from each other. Curiously, they are also naturally very distant from each other, geographically speaking. This might be explained by the fact that chalcone isomerases have been found in bacteria,²¹ thus cardamonin could be the result of an uptake of a previously produced compound, or precursor, in the plant's rhizosphere by the actinomycetes present there. Nevertheless, and not surprisingly, since it includes cardamom spice, the Zingiberaceae family is the most represented.

Table 1.

Sources of Cardamonin Organized Taxonomically

Kingdom	Division	Class	Order	Family	Genus	Species	Reference
Plantae	Magnoliophyta	Liliopsida	Zingiberales	Zingiberaceae	Alpinia	Alpinia blepharocalyx	23, 24
						Alpinia conchigera	26, 27
						Alpinia gagnepainii	25
						Alpinia hainanensis	28–40
						Alpinia malaccensis	41
						Alpinia mutica	42, 43
						Alpinia rafflesiana	45–48
						Alpinia speciosa	22, 49, 50
					Amomum	Amomum subulatum	51
					Boesenbergia	Boesenbergia pandurata	53–60
						Boesenbergia rotunda	61, 62
					Elettaria	Elettaria cardamomum	68
					Kaempferia	Kaempferia parviflora	54
		Magnoliopsida	Asterales	Asteraceae	Artemisia	Artemisia absinthium	52
					Helichrysum	Helichrysum forskahlii	69
			Juglandales	Juglandaceae	Carya	Carya cathayensis	63
			Lamiales	Verbenaceae	Vitex	Vitex leptobotrys	79
			Magnoliales	Annonaceae	Desmos	Desmos cochinchinensis	67
			Myricales	Myricaceae	Comptonia	Comptonia peregrina	66
					Morella	Morella pensylvanica	66
			Myrtales	Combretaceae	Combretum	Combretum apiculatum	65
				Myrtaceae	Syzygium	Syzygium samarangense	78
			Piperales	Piperaceae	Piper	Piper dilatatum	70
						Piper hispidum	71
			Polygonales	Polygonaceae	Polygonum	Polygonum ferrugineum	72
						Polygonum lapathifolium	73
						Polygonum persicaria	74, 75
			Salicales	Salicaceae	Populus	Populus fremontii	76
						Populus x euramericana	77
			Sapindales	Rutaceae	Cedrelopsis	Cedrelopsis grevei	64
	Pteridophyta	Filicopsida	Polypodiales	Dryopteridaceae	Woodsia	Woodsia scopulina	80

Health Applications

Anti-inflammatory, antineoplastic, and antioxidant activity

Several authors^{26,36,46,52,81} have aimed to explain the anti-inflammatory activity of cardamonin by fully observing its influence over the signaling pathway of the nuclear factor-κB (NF-κB)—a protein complex that controls transcription of DNA and plays a crucial role in regulating immune responses to infection^1,82—and detail the mechanism of action on the lipopolysaccharide (LPS)-induced inflammatory gene expression. A 27% inhibition of LPS-induced NO production with a 1 μM can be found in literature.⁸³ Its interference over the NF-κB pathway and subsequently, the p65NF-κB protein cellular distribution inhibits cyclooxygenase-2 and inducible nitric oxide synthase.⁴⁷ It also appears to end up inhibiting prostaglandin E2, tumor necrosis factor α (TNF-α) release, thromboxane B2 production, and intracellular reactive oxygen species generation, all in a dose-dependent manner.^48,54 In most of these studies, RAW264.7 cells were used and analyzed by enzyme-linked immunosorbent assays, western blotting, and interestingly, luciferase gene reporter assays.⁸⁴

Wei et al.³⁷ studied the protective effect of cardamonin from acute lung injury in sepsis. Sepsis is a generalized inflammatory response that can be lethal by organ failure; one of the organs commonly affected are the lungs resulting in hypoxemia and pulmonary edema. Studies were carried out in mice, and results showed that cardamonin decreases systemic inflammatory responses, during sepsis, by downregulating TNF-α and interleukins (in this case, IL-1β and IL-6).

Dong et al.²³ showed that cardamonin can inhibit arachidonic acid-induced platelet aggregation in human whole blood; authors used indomethacin as a positive control. Similar positive results were obtained by Jantan et al.⁴² (IC₅₀=73 μM), acetylsalicylic acid was used as a positive control instead (IC₅₀=27 μM) for an arachidonic acid concentration of 500 μM. Acetylsalicylic acid was also used as a positive control in a different study⁵⁸; in such study, a 4.6% inhibition on carrageenan-induced hind paw edema (with acetylsalicylic acid, a 52.9% inhibition was obtained) with 300 mg/kg given orally. Cardamonin's effect over the platelet activating factor receptor binding was tested and a 42% inhibition value (cedrol, the positive control, in the same conditions gave a 74% value)⁴³; experiments were carried out with rabbit platelets.

It is now known that the unregulated NF-κB pathway plays a key role in neoplastic processes. Not surprisingly, several studies showing cardamonin's antimutagenic activity have also been published. Qin et al.⁸⁵ showed that cardamonin has a potent activity against multiple myeloma; studies were performed on human multiple myeloma cell lines (RPMI 8226, U266, and ARH-77) and results clearly indicated an antimyeloma activity by inhibiting the growth and proliferation of the mentioned cell lines. Cardamonin also appears to have an enhancement effect on the TRAIL-induced apoptosis, a promising target for selective cancer therapy.^49,86 Cardamonin was tested in several cancer cell lines, namely, HuCCA-1—human cholangiocarcinoma cancer cells, HepG2—human hepatocellular liver carcinoma cell line, A549—human lung carcinoma cell line, and MOLT-3—T-lymphoblast (acute lymphoblastic leukemia) cell line.⁶⁷

Lin et al.⁴⁴ tested some chalcones effects, including cardamonin, upon cell death of human squamous carcinoma KB cells. With solutions of 74 μM, a viability of ca. 50% was obtained for periods of 24, 48, and 72 h. Cardamonin has shown a preferential cytotoxicity (PC₁₀₀) against human pancreatic PANC-1 cancer cells in a nutrient-deprived medium superior to 256 μM.⁵⁹ In this study, where arctigenin was used as a positive control, with other compounds extracted from Boesenbergia pandurata, including a chalcone, lower PC₁₀₀ values were obtained.

Trakoontivakorn et al.⁵⁵ extracted cardamonin from finger-root and tested its antimutagenic activity against heterocyclic amines. They obtained a result of 6% inhibition of the N-hydroxylation of 3-amino-1-methyl-5H-pyrido[4,3-b]indole, with methanol being the control. Morikawa et al.⁶² obtained with a 30 μM, a 37% inhibition on the aminopeptidase N activity (a metalloprotease that plays an important role in tumor cell invasion, extracellular and tumor metastasis), curcumin being the reference compound.

Results obtained in trials with the Epstein-Barr virus (EBV) also point to cardamonin as an effective inhibitor of tumor promoter.⁵⁶ EBV, is a virus from the Herpesviridae family also named as human herpes virus 4 (HHV-4), which is widely known for causing infectious mononucleosis; however, it is now recognized that it is also implicated in the promotion of several types of neoplastic processes such as Hodgkin's lymphoma. An interesting IC₅₀ of 3.1 μM in studies on the inhibition of EBV activation, whereas an IC₅₀ of 1.5 μM was obtained for acetoxychavicol acetate considered by the authors as a “highly potent EBV activation inhibitor.”

Cardamonin showed potent antioxidant activity in an oxygen radical absorbance capacity assay.⁶⁷ However, Li et al.⁸⁷ did not find any relevant antioxidant activity in DPPH and superoxide anion assays at least in the concentrations they tested (as low as 1 μM). Simirgiotis et al.⁷⁸ extracted cardamonin from wax jambu fruits and carried on experiments concluding that it had a fifth of the IC₅₀ of gallic acid antioxidant activity in DPPH assays and 70% of the cytotoxic activity of epigallocatechin gallate in assays with SW-480 human colon cancer cell lines. Li et al.⁸⁷ also found relevant cytotoxic activities in hepatoma cells HepG2 cells (IC₅₀=31 μM) being, however, also cytotoxic with normal liver L-02 cells (IC₅₀=23 μM). A larger result for HepG2 cells can also be found in literature (IC₅₀>100 μM) in the same trials, where an IC₅₀ of 46 μM was obtained for Helacyton gartleri.⁶³ Aderogba et al.⁶⁵ evaluated cardamonin's toxicity using the 3-(4,5-dimethylthiazol)-2,5-diphenyl tetrazolium bromide (MTT) assay on Vero African green monkey kidney cells, it actually had a lower LC₅₀ (7.3 μM) than the positive control berberine (37 μM). A 10% to 20% antioxidant activity was also found with a 50 μM concentration using vitamin C as the positive control.⁸⁸

Vasorelaxant activity

Fusi et al.⁸⁹ showed that cardamonin can be vasodilator by inhibiting the entry of calcium to the cell by the voltage-dependent Ca_v2.1 channel and stimulating the exit of potassium by the calcium-activated KCa1.1 channel. Studies were performed in rat tail artery miocytes. Wang et al.⁴⁰ concluded that cardamonin can be a vasorelaxant, trials were done on rat isolated main superior mesenteric arteries. An IC₅₀ of 9 μM was obtained with the artery preconstricted with phenylephrine. Huang et al.²⁴ also made studies in the main branch of the superior mesenteric artery, they also concluded that cardamonin induced both endothelium-independent and -dependent relaxation.

Hypoglycemic activity

Yamamoto et al.³⁴ recently showed that cardamonin promotes the uptake of glucose by glucose transporter-4 (GLUT4), an insulin-sensible mediator of glucose from the cytosol to the plasma membrane in muscle cells and adipocytes, usually postprandially active by insulin. Efficient control of GLUT4 is very relevant to the treatment of diabetes mellitus type 2. Studies were performed in L6 myotubes and results showed that a 30 μM cardamonin solution could stimulate GLUT4 for about 1 to 4 h in similar levels to a 0.10 μM insulin solution. Previously, Liao et al.³⁵ had already shown that cardamonin could inhibit the proliferation of insulin-resistant cells. Studies were performed on rats previously induced to be insulin resistant by a 12-week diet rich in fructose.

Anti-infectious activity

Cardamonin, extracted from Piper hispidum, showed to be cytotoxic toward amastigotes of Leishmania amazonensis. The concentration inhibiting 50% of the parasite growth (IC₅₀) was calculated to be 8 μM, while with the reference amphotericin B, IC₅₀ was 0.2 μM. However, the fact that it did show some mild toxicity against peritoneal macrophages⁷¹ may complicate the development of pharmaceuticals against leishmaniasis (a still worrying disease caused by parasites from the genus Leishmania).

In addition, quite recently, López et al.⁷² found cardamonin in a Polygonum, and the studies performed lead them to conclude that cardamonin has antifungal activity toward Epidermophyton floccosum (anthropophilic dermatophyte that can cause athlete's foot and onychomycosis among others), however, it did not show any noteworthy activity against other fungi like Candida albicans, Saccharomyces cerevisiae, or Cryptococcus neoformans. The antifungal evaluation was performed over cell lines of all the mentioned fungi in an agar dilution method. Scanning electron microscope studies further made the authors conclude that the antifungal mechanism of action is of type wall inhibitor. Similar results of irrelevant activity against S. cerevisiae and C. albicans had been previously obtained²⁷ along with insignificant activity results against the fungi Fusarium oxysporum and Aspergillus niger, however, a 25 μg/mL minimum inhibitory concentration (MIC) was obtained for the bacteria Staphylococcus aureus and Escherichia coli and 50 μg/mL MIC for Bacillus subtillis. Derita et al.⁷⁵ also found some minor activity against Microsporum gypseum, Trichophyton rubrum, and Trichophyton mentagrophytes, all fungi responsible for dermatophytoses.

Tewtrakul et al.⁵³ obtained interesting results concerning the cardamonin ability to inhibit HIV-1 protease, a crucial enzyme in the lifecycle of HIV-1. In this study, cardamonin had an IC₅₀ of 115 μM, while the positive control (acetyl pepstatin) has an IC₅₀ of 0.50 μM. Posterior studies also showed, however, some inhibitor effects over the dengue virus type 2 (DV2) NS3 protease.⁶¹ Dengue is still endemic over 100 countries and there is no vaccine available so far or even any specific treatment. No positive control was used in the study; inhibition was assumed using the Lineweaver-Burk plot, whereas cardamonin had a 71% and 39% inhibition rate with a 2 μM dengue-2 protease complex using concentration of 1480 and 444 μM, respectively. Theoretical simulations about how cardamonin interacts with DV2 protease can also be found in literature.⁹⁰

Miscellaneous

Cho et al.⁹¹ showed that cardamonin can inhibit melanogenesis by melanocytes (cells located in the stratum basale of the skin's epidermis). Cardamonin appears to suppress the Wnt signaling pathway and could possibly be used as a potential whitening agent in cosmetics as well as in the treatment of hyperpigmentation disorders.

Huang et al.³² obtained results of antiemetic activity in trials with a young quail, with a 100 mg/Kg dose, they have obtained a 52% inhibition rate.

Recently, Hirata et al.⁹² observed that cardamonin inhibits cholesteryl ester transfer protein (CETP), the inhibition of this protein leads to the increase of HDL-cholesterol, however, with a significantly lower specific activity (ca. 5 nmol/mg/h) than xanthohumol (ca. 40 nmol/mg/h).

Pandji et al.⁶⁰ tested if cardamonin could be used in pest control (in trials with neonate larvae of Spodoptera littoralis), however, its efficiency as an insecticide was irrelevant.

Cardamonin metabolism was recently studied²⁸ in human P450 enzymes, results point to the isozymes CYP 1A2 and 2E1. Studies concerning the binding of cardamonin to serum albumin (the most abundant protein in human plasma, very important in the systemic transport of many relevant substances) had already been performed,⁹³ results lead to the conclusion that it binds site II (with an enthalpy change ΔH₀ of −25.3 kJ/mol and an entropy change ΔS₀ of 7.04 J mol⁻¹ K⁻¹). The binding to lysozyme has also been studied by spectroscopic methods⁹⁴: enthalpy change ΔH₀ of −12.1 kJ/mol and an entropy change ΔS₀ of 51.5 J mol⁻¹ K⁻¹. These are relevant information to the development of chalcone-based medication.

Analytical Methods

Zhang et al.²⁹ have analyzed cardamonin by a flow injection analysis method with a chemiluminescence detection based on the reaction between cerium (IV) and rhodamine 6G in an acidic medium, with a limit of detection (LOD) of 0.03 μM.

Wang et al.³⁰ used reverse micelle electrokinetic capillary chromatography to determine the compound with a LOD of 0.7 μM. Liu et al.³¹ also analyzed it by flow injection–micellar electrokinetic chromatography with a LOD of 13 μM. Recently, a HPLC-UV methodology has been developed with a LOD of 0.52 μM.³⁹

Cardamonin has been analyzed by square wave voltammetry on a hanging mercury drop electrode, the obtained LOD was of 0.55 μM,⁶⁸ with a peak potential of −1.0 V versus Ag|AgCl.⁹⁵

It has also been analyzed by electrospray ionization tandem mass spectrometry (ESI-MS). He et al.²⁸ did in negative mode with the following ions: MS—269, MS²—177, 165, 139, 124. Carvalho et al.⁶⁸ did in positive mode with the following ions: MS—271, MS2—167, MS3–139; as well as Terreaux et al.⁷⁰ and Ngo and Brown³⁸: MS—270, 193 and 167; and Itokawa et al.⁵⁰ 270, 269, 253, 193, 131, 103, and 77. It was determined by IR (KBr) first by Krishna and Chaganty²²—3170 (-OH), 1625 (C=O), and 970 cm⁻¹ (H-C=C-H)—and later by other authors—3400, 2924, and 1638 cm^{−1, 74} 3154, 1628, 1542, 1486, 1286, 1320, 1224, 1188, 1114, and 926 cm^{−1, 57} 3230, 3032, 2934, 2853, 1628, 1605 cm^{−1, 38} and 3140, 1630, 1495, 1340, 1220, 1180, 1120, 980, 795, and 750 cm⁻¹.^{50 1}H-NMR results can also be found in literature^{34,38,39,50,57,65,74} as well as 13C-NMR results.^22,50,57,74

Concluding Remarks

Cardamonin is another chalcone becoming increasingly relevant. Some authors claim that it appears to have anti-inflammatory, antineoplastic, vasorelaxant, hypoglycemic, and anti-infectious properties and the quest for potential health applications seems only to grow in the near future as shown clearly by the increasing number of publications. Nevertheless, since the number of articles is not the real qualitative measure of the compound's promising qualities in medicine and, as shown in this article, not all study results are significative (e.g., in some assays, it has shown low-level activity); researchers should be careful when approaching this molecule with high expectations. Furthermore, selectivity has not been fully studied; therefore, numerous side effects might be expected in future pharmaceutical formulations.

So far, cardamonin has been found in many different plants, but the pursuit for a cheap and an easily extractable source of cardamonin might still be of much interest, which will for sure be aided by all the analytical methodologies meanwhile developed.

Acknowledgments

This work has been supported by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) through grant no. PEst-C/EQB/LA0006/2011. IMV (SFRH/BD/69719/2010) and LMG (SFRH/BPD/76544/2011) wish to acknowledge FCT for her PhD studentship and his postdoctoral grant, respectively.

Author Disclosure Statement

All authors declare no competing financial interests or other conflict of interests.