Pharmacological Activities and Phytochemicals of Etlingera pavieana (Pierre ex Gagnep)

Etlingera pavieana (Pierre ex Gagnep) R.M.Sm. (Zingiberaceae family) is commonly found in Southeast Asia. The rhizome of the plant is used as a spice and folk medicine in southeastern Thailand and Cambodia. The extracts, essential oil, and compounds from E. pavieana were found to possess a variety of pharmacological activities like anti-inflammatory, antioxidant, antiatherogenic, and antimicrobial effects. Furthermore, phytochemical studies have reported the presence of various chemical constituents, the main being phenylpropanoids such as trans -4-methoxycinnamaldehyde (MCD) and 4-methoxycinnamyl p -coumarate (MCC). Therefore, E. pavieana seems to be a potential source of natural products for treatment of various diseases and promotion of good health.


Introduction
Plant-based nutraceuticals or functional foods have gained attention due to their health promotion and safety in comparison to synthetic food ingredients [1,2]. Presently, worldwide researchers have focus on scientific evaluation of medicinal plants to detect their pharmacological activities. Zingiberaceae family is distributed worldwide and comprises approximately 52 genera and 1587 species [3]. It is about 300 species belonging to 26 genera found in Thailand [4]. The plants in this family are the natural sources for traditional medicine, foods, spice, and other ethnobotanical uses [4]. Etlingera pavieana (Pierre ex Gagnep) R.M.Sm. is a member of the Zingiberaceae family and a medicinal plant of southeastern Thailand [5]. Several in vitro and in vivo pharmacological experiments and phytochemistry studies of E. pavieana have been reported. This chapter has presented comprehensive information about morphological characteristics, traditional uses, pharmacology activities, and phytochemical constituents of E. pavieana, which provide the data to plan future studies.
Recently, trans-4-methoxycinnamaldehyde, another compound isolated from E. pavieana rhizomes, suppressed the formation of NO and PGE 2 as well as the expression of their synthesizing enzymes, iNOS and COX-2, on LPS-and Pam3CSK4induced RAW 264.7 cells. The IC 50 values of NO and PGE 2 inhibition were 49.9 ± 4.7 and 87.6 ± 5.6 μM, respectively. The mechanism underlying anti-inflammatory activity of MCD could be inactivation of NF-κB and JNK/c-Jun signaling pathways [15]. Moreover, MCD showed a significant anti-inflammatory activity in rat models of acute inflammation. It was evident from this study that MCD (3 mg/ear) reduced ethyl phenylpropiolate (EPP)-induced ear edema by 51.5% inhibition. The second animal model used in this study was carrageenan-induced paw edema. Rats were orally administrated with MCD at doses of 75, 150, and 300 mg/kg for 1 h before injection with carrageenan. MCD can significantly decrease paw edema in a dosedependent manner at 1, 3, and 5 h after carrageenan stimulation. Since edema formation induced by EPP and carrageenan is attributed to a release of several inflammatory mediators [41,42], it is implied that the mode of MCD anti-inflammatory action in vivo model is mediated in part by suppression of inflammatory mediators. We also investigated anti-inflammatory effect of essential oil of E. pavieana leaves on LPS-induced RAW 264.7 macrophages. The essential oil of E. pavieana leaves at 25-100 μg/mL exhibited a concentration-dependent inhibition effect on NO production without significant cytotoxicity (Figure 3A). Incubation of cells with essential oil caused reduction of iNOS protein and mRNA expression (Figure 3B, C). The compound responsible for anti-inflammatory effect of essential oil of E. pavieana leaves might be methyl chavicol, a main phytoconstituent of this essential oil (unpublished data).

Antiatherogenic effect
Atherosclerosis is a chronic inflammatory disorder which leads to cardiovascular diseases (CVDs) [43,44]; it is a major cause of death in the world [24,45]. Endothelial dysfunction is an early step in the development of atherosclerosis. It involves with reduced NO bioavailability, low-grade inflammation, and oxidative stress [44,[46][47][48]. The initiation of atherosclerotic lesion is influenced by the expression of cell adhesion molecules including vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) on the vascular surface of the endothelial cells resulting in recruitment of leukocytes into the vascular tissue [49]. Inhibiting the expression of ICAM-1 and VCAM-1 leads to reduction of leukocyte emigration and retardation of the development of atherosclerosis. Thus, the substance that inhibits the expression of these cell adhesion molecules may be considered as anti-atherosclerosis agent that prevents vascular inflammatory disorders.
The rhizomal ethanol extract of E. pavieana was assessed for its anti-vascular inflammatory effect in human umbilical vein endothelial cells (EA.hy926 cells). Endothelial activation is upregulated by various pro-inflammatory cytokines, including TNF-α secreted under inflammatory conditions. The E. pavieana extract inhibited TNF-α-induced expression of ICAM-1 and VCAM-1 protein and mRNA in a concentration-dependent manner. The inhibitory effect of the rhizome extract in endothelial cells is caused from interfering with the activation of NF-κB and JNK/c-Jun signaling pathways. Moreover, Akt activation by E. pavieana rhizome is associated with negative regulation of inflammation. This anti-vascular inflammatory activity was attributed in part due to the presence of the two most active phenolic compounds of which were 4-methoxycinnamyl p-coumarate and trans-4-methoxycinnamaldehyde [50].
It is believed that decrease in endothelium-derived NO, produced by endothelial NO synthase (eNOS), results in reduced NO bioavailability [44,49]. Another study was carried out to demonstrate antiatherogenic effect of E. pavieana rhizome. EA.hy926 endothelial cells incubated with the ethanol extract of E. pavieana rhizome (12.5-200 μg/mL) caused increased NO level in a concentration-dependent manner. This induction might be partly mediated by the activation of eNOS enzyme via phosphorylation at Ser1177 [11].

Antioxidant effect
Accumulating evidences suggest that not only inactivation of eNOS enzyme but also increased superoxide level leads to the reduction in NO bioavailability [24,49]. Superoxide anion is produced by the mitochondrial electron transport chain and several enzymes in the endothelial cells. Superoxide anion is then oxidized to hydrogen peroxide and other physiological reactive species such as hydroxyl radical and hypochlorous acid [44]. Moreover, it reacts with NO to form highly reactive peroxynitrite leading to eNOS dysfunction [24,47]. Chronic inflammation is also closely associated with oxidative stress which generated excess ROS [24].

Antimicrobial activity
Various solvent extracts of E. pavieana (ethanol, acetone, dichloromethane, ethyl acetate, petroleum ether, and hexane) were found to be active against Gram-positive bacteria (Bacillus cereus, B. subtilis, Staphylococcus aureus, Listeria monocytogenes) and Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Vibrio parahaemolyticus, and Salmonella typhimurium). Antimicrobial activity of leaves was higher than that of stem and rhizome [12]. Tachai and Nuntawong demonstrated that hexane, dichloromethane, and methanol extracts of E. pavieana rhizomes were inactive against Mycobacterium tuberculosis, while MCC exhibited its antimicrobial activity against M. tuberculosis with minimum inhibitory concentration at 50 μg/mL [7].

Conclusion
In this chapter, we have provided the information on botanical aspects, dietary and traditional uses, phytochemicals, and pharmacological activities of Etlingera pavieana which is distributed in Southeast Asia. The major active compounds are phenylpropanoids such as trans-4-methoxycinnamaldehyde, and 4-methoxycinnamyl p-coumarate. Its rhizomes exhibit anti-inflammatory, antioxidant, antiatherogenic, antimicrobial, and anticancer activities. The pharmacological activities reported here confirm therapeutic efficacy of E. pavieana rhizomes which might be developed into medicines or nutraceuticals for the treatment and prevention of various diseases, especially inflammation-related diseases. However, in vivo toxicology studies of E. pavieana rhizomes should be performed along with the clinical trials.