Evaluation of Chemical Constituents and Important Mechanism of Pharmacological Biology in Dendrobium Plants

Dendrobium species, commonly known as “Shihu” or “Huangcao,” represents the second largest genus of Orchidaceae, which are used commonly as tonic herbs and healthy food in many Asian countries. The aim of this paper is to review the history, chemistry, and pharmacology of different Dendrobium species on the basis of the latest academic literatures found in Google Scholar, PubMed, Sciencedirect, Scopus, and SID.


Introduction
The origin of orchids (Orchidaceae) probably has to be backdated to 120 million years ago. It is the largest family group among angiosperms, as well as the most highly evolved family of the flowering plants, with approximately 25,000 to 35,000 species under 750 to 900 genera [1][2][3][4]. Dendrobium species, commonly known as "Shihu" or "Huangcao, " is the second largest genus in Orchidaceae. Most Dendrobium species grow best in relatively high and mountainous areas, at 1400-1600 m above sea level, at a mild temperature, and in a humid and foggy environment. Characterized by a broad geographical distribution, which allows Dendrobium species to grow into tremendous diversities producing a large number of interspecific hybrids with different morphological features, they are widely distributed in Asia, Australia, and Europe, for instance, in India, Sri Lanka, China, Japan, Korea, New Guinea, and New Caledonia [5]. In the early age, using molecular approaches would delimit the subtribe-Dendrobiinae, affecting approximately 1100 species (900 in Dendrobium Sw.) from Indo-Asian and Pacific regions [6,7], and more than 1200 species in Australasia are from various Dendrobium species. Today, Indo-Asian and Pacific regions have one of the largest and most diverse and taxonomically problematic orchid groups [8]. Interestingly, there has been a long history of the usage of first-rate herbs and folk traditional herbs in India and China [9].
Since the ancient times (600 B.C.) in India, the oldest references regarding the use of medicinal herbs are found in the Sanskrit literature, namely, "Charaka Samhita. " The earliest treatise on "Ayurveda" describes the property of plant drugs and their uses. In the Ayurvedic system of medicine, Flickingeria macraei is used in "Ayurveda. " It is commonly named as "jeevanti" and is used as an astringent to the bowels, as an aphrodisiac, and in asthma and bronchitis [10]. Other commonly used orchid drugs in the Ayurvedic system are salem, including jewanti (Dendrobium alpestre). Similarly, it is the first time for China to regard orchids as herbal medicines [11]. The Emperor "Shen-Nung" advised on the medicinal properties of Dendrobium species in "materia medica" in the 28th century B.C. [12]. As early as 200 B.C., the Chinese pharmacopoeia "The Sang Nung Pen Tsao Ching" mentioned Dendrobium as a source of tonic, astringent, analgesic, and anti-inflammatory substances [13]. In Song Dynasty (960-1279 A.D.). It mentioned the medicinal uses of orchids, namely Dendrobium species according A Diagnosis of Medical Herbs from the "Zheng Lei Ben Cao". In Ming Dynasty (1368-1644) many references on the use of orchids as medicinal herbs were available [14].
However, cells possess two distinctive antioxidant defense systems to counteract the damage, including enzymatic antioxidants and nonenzymatic antioxidants. Enzymatic antioxidants comprise catalase, superoxide dismutase (SOD), glutathione peroxidase (GPx), and others associated with enzymes/molecules. Nonenzymatic antioxidants include ascorbic acid (vitamin C), -tocopherol (vitamin E), andcarotene, which play a key role in removing reactive oxygen species.
Oxidative stresses have been classified as exogenous factors and endogenous factors. Factors related to environmental stress include water/soil drought stress, chilling injury stress, and sound wave stress. There were studies on the effects of cold storage on cut Dendrobium inflorescences, showing that chilling injury symptoms for floral buds and open flowers of Dendrobium could lead to oxidative stress, stemming from the production of reactive oxygen species. In this process, the decrease of cellular functions by peroxidation of membrane lipids when lipoxygenase enzymes are degraded in cells. However, this physiological process in floral buds and open flowers is part of antioxidant defense systems, which can decrease the content of oxygen free radicals and other oxygen compounds. It indicates the protective cellular functions and antioxidant capacity. This is an adaptive nature to ensure some plants survive in the freezing winter [62].
In addition, sound wave stress is one of the environmental stresses, similar to the low temperature stress. Studies of the effects of sound wave stress on D. candidum yielded data indicated it as a lipid peroxidation parameter which can regulate the levels of MDA. Firstly, the MDA content in different organs is increased and then declines afterwards, which will then be followed by an increase again. That gives a net increase of the level of MDA. It was noted that the MDA level appears to be the lowest when the activities of antioxidant enzymes are the highest. However, the levels of MDA are yet to be fully understood. We believe the antioxidant enzymes could protect plant cells from oxidative damage in sound wave stress [63]. However, the correlation between the mechanisms of antioxidant action and the sound wave stress and chilling injury stress has yet to be identified.
Water deficit caused by soil drought is one of the most frequent environmental stresses. The effects of exogenous drought menace, prompting further increases in the activity of ROS and decrease in the malondialdehyde (MDA) content, to prevent the breakage of DNA and protein degradation from doing damage to plant life [64]. It is well known that nitric oxide (NO) is a ubiquitous signal molecule involved in many life processes of plants, seed germination, hypocotyl elongation, leaf, expansion, root growth, lateral roots initiation, and apoptosis, and so forth. It is also involved in multiple plant responses to environmental stress. Data demonstrated that, at lower concentrations of exogenous NO with 50 mmol L −1 SNP, the activation of POD, SOD, and CAT was significantly increased, and the MDA content decreased with 50Ml SNP.NO could protect D. huoshanense against the oxidative insult caused by a drought stress; meanwhile, a high level of RWC can be maintained. Furthermore, it suggests that the molecular messenger NO can trigger epigenetic variation and increase the demethylation ratio of methylated sites for D. huoshanense by using DNA analysis. These results may imply that the expression of some genes is involved in the response to drought stress triggered by NO [65].
Up the table: the antioxidant effect of DNP4-2 on ABTS, hydroxyl, and DPPH free radicals, suggesting the levels of DNP4-2 higher than DNP1-1, DNP2-1, and DNP3-1; however, the antioxidant effects of DDP2-1 on hydroxyl and DPPH free radicals were higher than ABTS free radicals. Moreover, the DDP1-1 and DDP 3-1 on inhibitory effect were low than other compounds. We believe that the focus on antioxidant potential of DNP4-2 and DDP2-1 structures in near future.
action toward ABTS free radicals, and it also shows a weak DPPH free radical scavenging action. On the contrary, D. denneanum polysaccharide exerts a powerful DPPH free radical scavenging action, but its ABTS scavenging effect is not obvious [54]. In addition, both D. huoshanense and D. chrysotoxum polysaccharides reveal an insufficient ABTS free radical scavenging effect. However, it manifests potential hydroxyl radical scavenging activity. Overall, the free radical scavenging activities of polysaccharides on hydroxyl and DPPH free radicals remain at a high level, but the inhibitory effect on ABTS free radicals is weak. The above results, compared with other types of polysaccharides from D. denneanum and D. nobile, are shown in Tables 2 and 3, and others are shown in Table 4 : it is shown that DPPH and ABTS free radical scavenging (%) of DNP4-2 are better than other compounds; however, the hydroxyl free radical scavenging (%) of DNP is better than other compounds.
indicated that phenanthrenes and dihydrophenanthrenesin D. loddigesii have significant effects on inhibiting the production of NO and DPPH free radicals. These compounds are known as (numbered as 1a-7a) phenanthrenes (1a), phenanthrenes (2a), phenanthrenes (3a), phenanthrenes (4a), dihydrophenanthrenes (5a), dihydrophenanthrenes (6a), and dihydrophenanthrenes (7a). Based on the above results, the scavenging activity of loddigesiinols toward NO free radicals is pronounced. The inhibitory actions of phenanthrenes and dihydrophenanthrenes from D. loddigesii on the production of NO and DPPH free radicals are recognised. The relevant data and information are shown in Table 5 [71].
sanene on iNOS mRNA induced by LPS in mouse peritoneal macrophages. Meanwhile, there are several inflammatory cytokines, such as TNF-, IL-8, and IL-10, which were inhibited. Thus, the beneficial effects of dendrochrysanene compounds as anti-inflammatory agents were identified [72].

Sjögren's Syndrome (SS).
Sjögren's syndrome (SS) is a chronic autoimmune disease with disorder of the exocrine glands. The symptoms are dry eyes, dry mouth, dry throat and thirst with blurred vision, and so forth. The abnormal distribution of salivary glands in SS leads to an inflammatory effect and pathological processes triggering lymphocyte infiltration and apoptosis. Lymphocyte infiltration and apoptotic pathways, shown by regulation of Bax, Bcl-2, and caspase-3, have been reported in submandibular glands (SG). Furthermore, in pathological processes were also found that the subsequent signal of cell expression to mRNA of proinflammatory cytokines, such 30 as tumor necrosis (TNFa), interleukin (IL-1 ), and IL-6. As well as, a high level of expression of aquaporin-5 (AQP-5) is identified. AQP-5 is one of a water channel protein, and plays an important role in 31 the salivary secretions [73,74]. Treatment with D. officinale polysaccharides (DP) could suppress the progression of lymphocyte infiltration and apoptosis in SS and rectify the chaos of proinflammatory cytokines including TNF-, IL-1 beta, and IL-6 in SG [71,75] (Figure 1). mRNA expression of TNF-was inhibited. The process of regulation resulted in a series of marked responses, such as translocation of NF-B, prolonged MAPK, cytochrome C release, and caspase-3 activation, which have been identified [55,76]. In addition to the findings on DP treatment, there are reports on the findings on the extracts of D. candidum and D. nobile.
A clinical study found that, after 1 week of oral administration of the extract of D. candidum, salivary secretion was increased by approximately 65%. The extract promoted the expression of aquaporin-5 useful for treatment of Sjögren's syndrome (SS).
Chrysotoxine isolated from D. nobile can increase the expression of AQP-5 in dry eyes, one of the symptoms of SS, and restore the distribution of AQP-5 in lacrimal glands and corneal epithelia, by inhibiting the release of cytokines, such as IL-1, IL-6, and TNF-. In the meantime, it can activate the mitogen-activated protein kinase (MAPK) signaling pathways. Furthermore, it elicits an increase in the production of matrix metalloproteinase-9 (MMP-9). Ultimately, it leads to an increase of saliva and tear secretion. The medical efficacy of the extracts of D. officinale, D. nobile, and D. candidum species has been demonstrated [43] (Figure 1).

Neuroprotective Effect (Parkinsonian Syndrome).
Five bioactive derivatives isolated from Dendrobium species, namely, chrysotoxine (CTX), moscatilin, crepidatin, nobilin B, and chrysotobibenzyl, are potential neuroprotective compounds with antioxidant activity which can be used in the treatment of Parkinson's disease (PD). The IC 50 values of DPPH free radical scavenging activities of chrysotoxine (CTX), moscatilin, crepidatin, and nobilin B were 20.8 ± 0.9, 28.1 ± 7.1, 38.2 ± 3.5, and 22.2 ± 1.4, respectively. The above data show that crepidatin is better than other compounds in DPPH free radical scavenging capacity. CTX could selectively antagonize MPP + in dopaminergic pathways in the brain; also 6-hydroxydopamine (6-OHDA) has been inhibited by mitochondrial protection and NF-B modulation in SH-SY5Y cells. Thus, it could explain how it may be beneficial in preventing PD [44,77].
In addition, results of CTX compound in Dendrobium nobile Lindl. used in treatment of PD have also been clearly reported. We evaluated the pharmacokinetics of oral (100 mg/kg) and intravenous (25 mg/kg) administration of CTX preparation using high performance liquid chromatography-tandem mass spectrometric (HPLC-MS/MS) method in animal tests [78]. Results indicate efficacy  and safety in treating PD conditions. The antioxidant mechanisms towards 6-OHDA and SH-SY5Y and regulation of antiapoptosis in cell signaling pathways were described [52].

Immunomodulatory Activity.
Lymphocytes can be classified as T lymphocytes, B lymphocytes, and macrophages, respectively. They are important to immune cells and play a key role for reactions and responses in the immune system. Generally, there are various types of lymphocytes which are activated by very complex signal transduction pathways. Among all, the most common type is the action of lipopolysaccharides (LPS) in macrophages, which are able to produce many different kinds of proinflammatory cytokines, especially TNF-, which is one of the main proinflammatory cytokines and plays a critical role in mediating signal transduction and stimulating the immune defense system [79]. The immunopotentiating action from Dendrobium species produced by concanavalin A-(Con A-) stimulated proliferation of splenocytes in mouse. Finding the part of, which the D. officinalis produced a more potent immunopotentiating action, although it did not provided related to information of biological activity [57]. Sesquiterpenes from D. nobile showed a comitogenic effect on Con A-and LPS-stimulated mouse splenocytes. Other chemical components, including polysaccharides and sesquiterpene glycosides were also confirmed. Related sesquiterpene glycosides with alloaromadendrane, emmotin, and picrotoxane type aglycones, namely dendroside A, dendronobilosides A. In vitro biological tests suggest the types of polysaccharides and sesquiterpene glycosides (given as dendrosides D-G) significantly promoted cell proliferation and more stimulation of mouse T and/or B lymphocytes [45,80]. On the other hand, compounds from D. moniliforme, namely, dendroside A, dendroside C, and vanilloloside, were found to stimulate the proliferation of B cells and inhibit the proliferation of T cells in vitro [46] (Table 6).
In addition, the leaf, stem (cell walls), and mucilage isolated of D. huoshanense using chemical and enzymatic analyzed by chromatographic and spectroscopic methods, results demonstrated the bioactivity from polysaccharides and it's structure, HPS-1B23. The potential effects for main composed of more monosaccharides, showing Xyl, Ara, Man, Glc, Gal, and GalA, by HPS-1B23, signify an increasing immunostimulating activity through upregulating the levels of several cytokines, including TNF-, IL-10, IL-6, and IL-1 [47]. In addition, the stem cell mucilage polysaccharides of D. huoshanense composed of -(1-4)-D-Glcp and -(1-4)-D-Manp linkages with partial acetylated mannosides were identified, which upregulated the growth factors GM-CSF and G-CSF. DHP-4A stimulated RAW 264.7 macrophages to secrete NO, TNF-, IL-6, and IL-10 by activating p38, ERK, JNK, and NF-B. The results provide clear scientific  evidence on regulation of hematopoietic growth factors and cytokines factors in the immune system by different polysaccharides from D. huoshanense [81,82]. Interestingly, the total polysaccharides of D. huoshanense induced the expression of interleukin-1 receptor antagonist (IL-1ra) in human monocytes. Which the IL-1ra was regulated by 37 a series of signaling pathways, like ERK/ELK, p38 MAPK, PI3K, and NF-B [83].
In addition, the water-soluble polysaccharides (DTP) derived from D. tosaense were isolated by using HPAEC-PAD, HP-SEC, GC-MS, and NMR spectroscopy. They significantly increased the number of natural killer (NK) cells, NK cytotoxicity, macrophage phagocytosis, and cytokine induction in splenocytes, when administered orally to BALB/c mice for 3 weeks [59].

Treatment of Diabetes. The compounds isolated from
Dendrobium huoshanense (DHP) have been evaluated for treatment of diabetes in recent years. The hypoglycemic and antioxidative activities of three polysaccharides, namely, D. officinale (DOP), D. nobile (DNP), and D. chrysotoxum (DCP), have been compared in diabetic mice. Result showed that the hypoglycemic effect of DHP was better than those of DNP and DOP. In addition, the antioxidant effect of DHP was better than those of DOP and DNP by regulating the superoxide dismutase, catalase, malonaldehyde, and lglutathione levels in the liver and kidney. Thus, the hypoglycemic and antioxidant activities of DHP need to be studied more extensively in the future [60].
On the other hand, erianin, a phenanthrene from D. chrysanthum, is recognized as an antitumor agent. Reports showed that it has potent inhibitory activity in hepatoma Bel7402, melanoma A375, and HL-60 cells, as evidenced by inhibition of angiogenesis and induction of endothelial cytoskeletal disorganization in vivo and in vitro, but did not show antitumor activity [56,61]. Thus, further investigation is needed to identify if the antitumor mechanisms of erianin and denbinobin are similar.
The  [48]. In addition, denbinobin is a major phenanthrene isolated from stems of D. nobile. The inhibitory mechanisms of denbinobin in SNU-484 cells have been observed. It significantly decreased the expressions of matrix metalloproteinase (MMP-2) and (MMP-9) and induced apoptosis through downregulation of Bcl-2 and upregulation of Bax in cancer cells. These findings may be used to provide reference for further studies on the pharmacological mechanisms from denbinobin and polysaccharides in D. nobile [50,51,84].

Antilymphoma Activity of Dendrobium formosum.
Lymphoma is a cancer of the immune system. The ethanolic extract of Dendrobium formosum showed antilymphoma activity in vitro as evaluated by the MTT assay. It also significantly prolonged survival time in Dalton's lymphoma bearing mice [85].
3.8. Antimicrobial Activity and Antifungal Activity. Dendrobium is an important economic plant; however, there have been certain cultivation issues yet to be resolved, particularly fungal infection [87]. Pythium vexans has been reported to cause stem rot, crown rot, root rot, damping-off, and patch canker in Dendrobium plants [88]. The diseases could lead to damage to the seedlings of D. chrysotoxum, D. chrysanthum, D. thyrsiflorum, and D. aurantiacum, characterized by water-soaked, brown or yellowish lesions with a brown margin, resulting in dieback of the plants within a few days Nobilin D, nobilin E, nobilone Inhibitory on NO production [42] (SR) Phenanthrenes Inhibition of LPS-induced of nitric oxide production [38] (SR) Dendroside A, Dendronobilosides A Immunomodulatory activity [43,44] (SR) Glycosides (dendrosides D-G) Significant Stimulation of the proliferation of mouse T and/or B lymphocytes [43,44] (SR) Polysaccharides (DNP-W1, DNP-W2, DNP-W3, DNP-W4) Anticancer activity [45] (SR) 4,7-Dihydroxy-2-methoxy-9,10-dihy Anticancer activity: [   3.11. Antiplatelet Aggregating Activity. Studies on the aggregation of platelets induced through thrombin, arachidonic acid (AA), thrombin, collagen, and platelet-activating factor (PAF) were conducted by using 4 different aggregation inducers. Animal tests disclosed that different Dendrobium species including Dendrobium loddigesii and Dendrobium densiflorum possess antiplatelet aggregating activity. The results indicated some compounds isolated from two Dendrobium species more effectively inhibited AA-induced aggregation than they inhibited aggregation induced by PAF and collagen [96]. In animal tests, the antiplatelet aggregation of D. loddigesii species, which those compounds in part from moscatilin, moscatin and diacetate. They inhibit platelet aggregation was induced by AA was completely abolished by fraction 4 (50 g/mL) in rabbit platelets. Meanwhile, further demonstrated there are strongly inhibited both AA and collageninduced platelet aggregations about 100 g/mL. However, in PAF there are no significant effects. In addition, comparison of different compounds from D. densiflorum species, such as moscatilin, homoeriodictyol, scoparone, scopoletin, and gigantol, which the antiplatelet aggregation activity of their were identified in vitro. Especially for scoparone has been reported to possess potent antiplatelet aggregation who more than other compounds. Thus, it possible interactied by compounds-compounds for antiplatelet aggregation [26,97,98] (Table 7).

Conclusion
In this paper, the history, chemistry, and pharmacology of different Dendrobium species are reviewed. Especially for biological pharmacology ( Table 7). The pharmacological activities examined include antioxidant, anti-inflammatory, immunomodulatory, antitumor, antimicrobial/antifungal,