Dendrobium officinale Kimura et Migo: A Review on Its Ethnopharmacology, Phytochemistry, Pharmacology, and Industrialization

Ethnopharmacological Relevance. Dendrobii Officinalis Caulis, the stems of Dendrobium officinale Kimura et Migo, as a tonic herb in Chinese materia medica and health food in folk, has been utilized for the treatment of yin-deficiency diseases for decades. Methods. Information for analysis of Dendrobium officinale Kimura et Migo was obtained from libraries and Internet scientific databases such as PubMed, Web of Science, Google Scholar, ScienceDirect, Wiley InterScience, Ingenta, Embase, CNKI, and PubChem. Results. Over the past decades, about 190 compounds have been isolated from Dendrobium officinale Kimura et Migo. Its wide modern pharmacological actions in hepatoprotective effect, anticancer effect, hypoglycemic effect, antifatigue effect, gastric ulcer protective effect, and so on were reported. This may mainly attribute to the major and bioactive components: polysaccharides. However, other small molecule components require further study. Conclusions. Due to the lack of systematic data of Dendrobium officinale, it is important to explore its ingredient-function relationships with modern pharmacology. Recently, studies on the chemical constituents of Dendrobium officinale concentrated in crude polysaccharides and its structure-activity relationships remain scant. Further research is required to determine the Dendrobium officinale toxicological action and pharmacological mechanisms of other pure ingredients and crude extracts. In addition, investigation is needed for better quality control and novel drug or product development.

(Chinese: 石斛, shihu) of Chinese materia medica [8]. In 2005 Chinese Pharmacopoeia (ChP), tiepishihu (Chinese: 鐵皮石 斛) was one species of medicinal shihu called Dendrobium candidum Wall. ex Lindl. [9]; however this Latin name was later disputed and considered the synonym of Dendrobium moniliforme (L.) Sw. [10,11]. In 2010 ChP, tiepishihu was renamed as Dendrobium officinale Kimura et Migo (aka Dendrobium officinale, Figure 1(a)). This Latin name was firstly denominated by two Japanese scholars in 1936 when they found the new species of Dendrobium in China [12]. Facilitating the preservation, the fibrous stems of Dendrobium officinale can be twisted into a spiral and dried as tiepifengdou (Figure 1(b)) or directly cut into sections and dried as well.
What is more, in 2010 ChP, tiepishihu was initially isolated as one single medicine; its processed stem was called Dendrobii Officinalis Caulis (valid botanical name: Dendrobium catenatum Lindl., taxonomic classification and synonyms in Table 1); in the meanwhile, Dendrobium nobile Lindl., Dendrobium chrysotoxum Lindl., Dendrobium fimbriatum Hook., and their similar species were collectively referred to as shihu [13].

Ethnopharmacological Use
The stems of Dendrobium officinale are mainly used as health food in folk. There are a variety of methods to enjoy its fresh stems, for example, chewing, juicing, decocting, and making dishes [14]. In addition, combining with other tonic Chinese herbs is viable, such as "Panacis Quinquefolii Radix" (xiyangshen, American Ginseng), "Lycii Fructus" (gouqizi, Barbary Wolfberry Fruit), and "Dioscoreae Rhizoma" (shanyao, Rhizome of Common Yam) [15]. As reported, the combination of Dendrobium officinale and American Ginseng could strengthen cell-mediated immunity, humoral immunity, and monocyte-macrophages functions of mice [16]. The functions and indications of tiepishihu and shihu are quite similar in traditional Chinese medicine (TCM) [17,18]. However, TCM physicians use shihu more frequently than tiepishihu. As precious medicinal materials, maybe the high price limits the application of tiepishihu. Because of the output promotion, Dendrobium officinale gradually got more applications, especially in recent decades. Research showed that low-grade fever after gastric cancer operations, atrophic gastritis, mouth ulcers, and diabetes were treated by the fresh Dendrobium officinale in TCM [19]. Combined with modern medicine, Dendrobium officinale can be used to treat many diseases including Sjögren's syndrome, gastric ulcer, alcoholic liver injury, chronic obstructive pulmonary disease, diabetes, obesity, rheumatoid arthritis, hypertensive stroke, cataract, weak constitution, or subhealth [2,[20][21][22]. However, these functions were from an earlier investigation and need further research to probe.

Polysaccharides.
Polysaccharides are the main component in dried Dendrobium officinale. Extraction and quantitative and qualitative analysis are described as follows, and the pharmacological effects of polysaccharides are in Table 3.

Extraction.
Generally, there are three methods that can isolate crude Dendrobium officinale polysaccharides (DOP): a solvent method (water extraction by alcohol sedimentation), a biological method (enzyme extraction), and a physical method (ultrasonic extraction and microwave extraction). Among the three, the solvent method is most popular. The physical method could be combined with the biological and solvent methods to accelerate the extraction process and promote the efficiency [23].
Since there are lipids, proteins, pigments, and other impurities after the process of separation of polysaccharides, other separation methods, such as ion-exchange chromatography, gel filtration chromatography, and HPLC, are needed to purify the crude polysaccharides [24]. However, polysaccharides are acknowledged as complex biological macromolecules; the ways and sequences of connections of the monosaccharides determine the difficulty of polysaccharides' analyses [25].      inhibition of gastric injury rate [75] Squeezing then filtration In vivo Gavage 0.5 and 2 g/kg Declined irritable and chemical gastric ulcer model's ulcer indexes in mice [76] 10 Evidence-Based Complementary and Alternative Medicine In vitro -0.1, 1.0, and 10 g/mL Ameliorated the abnormalities of aquaporin-5 (AQP-5) on A-253 cell [79] Water extract and alcohol precipitate, extraction rate: 29.87% In vivo Smear 5.0 g/L Increased average score and average quality of hair growth of C57BL/6J mice [80] in vitro

Quantitative and Qualitative
Analysis. The average content of neutral sugar in desiccated Dendrobium officinale is up to 58.3% [26]. Actually, different production origins, processing methods, growing years, and cultivated or wild and different parts of Dendrobium officinale are all related to polysaccharide content. Research showed that there were various polysaccharide contents of the same species cultivated in Guangdong with different origins from Yunnan, Zhejiang, and other provinces [27]. After drying each with different methods, DOP content was arranged as follows: hot air drying > vacuum drying > vacuum freeze drying > natural drying [28]. In addition, amounts of polysaccharide were greater in biennial Dendrobium officinale than annual or triennial ones [29], while the wild type contained more content compared to the cultivated type [30]. Research showed that polysaccharides distributing in different parts of Dendrobium officinale varied: middle stem > upper stem > lower stem > roots [31]. Therefore, accurate determination of polysaccharide content is of great significance. Fourier Transform Infrared Spectrometer (FT-IR), Gas Chromatography-Mass Spectrometer (GC-MS), and 1 H and 13 C NMR spectroscopies have been used to analyze the types of monosaccharide residues and the linkage sites of glycosidic bonds [32]. However, the research of polysaccharide's ratio of mannose to glucose, the existence of branches, and the substitution position of o-acetyl groups was inconsistent [33]. What is more, polysaccharides' pharmacological activities are strongly linked to the composition and content of their monosaccharides [26]. Therefore, further methods to explore the advanced structures and structure-activity relationships of Dendrobium officinale polysaccharides need to be established. Research showed that O-acetyl-glucomannan, Den-dronan5 ( Figure 2, A), from Dendrobium officinale [34] has been isolated and was affirmed immunomodulatory activity in vitro [35] and in vivo [36], as well as improvement in colonic health of mice [37].

Phenanthrenes.
From Dendrobium officinale, nine phenanthrenes ( -) were isolated. Dendrobium officinale contains a kind of bibenzyl and a kind of phenanthrene identified in D. chrysotoxum before: chrysotobibenzyl ( ) and erianin ( ). Both chrysotobibenzyl and erianin have antitumor effects. Erianin significantly inhibited the proliferation of HepG2 and Huh7 (human hepatoma cell lines) in vitro [38] and also prevented angiogenesis in human hepatoma Be17402 and human melanoma A375 in vivo [39].

Saccharides and Glycosides.
In the last few decades, at least 26 saccharides and glycosides have been found from Dendrobium officinale, (compounds -). Among them, Dictamnoside A ( ) showed immunomodulatory activity in mouse splenocyte assessed as stimulation of proliferation at 10 umole/L after 44 hours by MTT assay in the presence of Concanavalin A (ConA) [43].

Alkaloids.
Alkaloids are the earliest chemical compounds isolated from Dendrobium genus. Dendrobine, a kind of Dendrobium alkaloid accounting for 0.52%, was isolated initially in 1932 [47]. It was later proved to be the special content of D. nobile [48]. As reported, the alkaloid in Dendrobium officinale belongs to the terpenoid indole alkaloid (TIA) class, with its total content measured at approximately 0.02% [49]. However, the isolation and identification of one single kind of alkaloid have been rarely reported.

Pharmacological Effects of Dendrobium officinale
Recently, more and more pharmacological actions of Dendrobium officinale were reported, such as hepatoprotective effect, anticancer effect, hypoglycemic effect, antifatigue effect, and gastric ulcer protective effect (Table 3).

Hepatoprotective Effect. The hepatoprotective capacity of
Dendrobium officinale is always related to its antioxidant ability, especially in acute or chronic alcoholic liver injury.
Research showed that Dendrobium officinale polysaccharides (DOP) accelerated the metabolism of serum TG and TC, while increased liver ADH and ALDH activities, which recovered disorders of lipid metabolism and accelerated excretion of alcohol and its metabolites [64]. In addition, ALT, AST, and TC of Dendrobium officinale treated mice models with chronic alcoholic liver injury were elevated compared to the normal groups [65]. Besides, compared to the model group   of mice with acute alcoholic hepatic injury, fresh Dendrobium officinale and tiepifengdou groups could increase the SOD and reduce MDA of serum and liver tissue [66].

Anticancer Effect.
The anticancer activity of Dendrobium officinale extract has been studied and proved, such as anti-HelaS3, anti-HepG2, and anti-HCT-116 in vitro, as well as anti-CNEl and CNE2 in vivo and in vitro [69]. Besides, DOP has manifested anticancer effects in mice with Lewis lung carcinoma (LLC). Its tumor inhibition rate was 8.5%-18.3% ( > 0.05); meanwhile, LLC mice spleen lymphocyte transformation and hemolysin levels ( < 0.05) were improved [67]. In cellular experiments, Liu's morphological analysis showed that DOP can inhibit the growth of human hepatoma cells (HepG2), human lung cancer cells (A549), human teratoma stem cells (NCCIT), and murine teratoma stem cells (F9) and promoted the proliferation of mouse spleen cells in vitro [68]. Research showed that two DOP fractions, DOP-1 and DOP-2, promoted splenocyte proliferation, enhanced NK cell-mediated cytotoxicity, and increased the phagocytosis and nitric oxide production of macrophages significantly ( < 0.05) [82]. Therefore, the anticancer effect of Dendrobium officinale may be accompanied by the activity of improving immune system.

Hypoglycemic Effect.
Hypoglycemic activity, another important property of Dendrobium officinale, has been studied a lot. Oral administration of DOP decreased levels of fasting blood glucose (FBG) and glycosylated serum protein (GSP) and increased level of serum insulin in alloxaninduced diabetic mice. In addition, DOP attenuated the occurrence of oxidative stress in the liver and kidney of alloxan-induced diabetic mice by decreasing MDA levels, increasing GSH concentrations and antioxidative enzyme activities [70]. Therefore, DOP may regulate blood sugar levels through blood-lipid balance effects and antioxidative damage effects of liver and kidney.
Dendrobium officinale exhibited a significant hypoglycemic effect in adrenaline hyperglycemia mice and streptozotocin-diabetic (STZ-DM) rats [71]. In addition, TP (total polysaccharides, 100 mg/kg), TF (total flavonoids, 35 mg/kg), and TE (water extract, 6 g/kg) groups of Dendrobium officinale significantly downregulated the phosphorylation of JNK (Thr183/Tyr185) and upregulated the phosphorylation of AKT ser 473 compared with the normal control group, which indicates that effective extracts of Dendrobium officinale have the effects of inhibiting JNK phosphorylation and promoting AKT ser 473 phosphorylation [72].

Antifatigue Effect.
The antifatigue effect of Dendrobium officinale was illustrated in vivo, when compared with the control groups; Dendrobium officinale could increase the glycogen stored in mice after exercise and decrease the level of serum urea and lactic acid accumulation ( < 0.05 or < 0.01). In addition, it could upregulate the expression of ciliary neurotrophic factor (CNTF) mRNA ( < 0.05 or < 0.01) [73]. In addition, compared to the control groups, Dendrobium officinale significantly increased carbon clearance indexes and burden swimming time and reduced the serum lactic acids [74]. In general, antifatigue effect of Dendrobium officinal was linked to the TCM use about enriching consumptive diseases, but its mechanism needs to be further clarified.

Gastric Ulcer Protective Effect. Research showed that
Dendrobium officinale had a preventive effect of gastric injury caused by 60% ethanol-hydrochloric acid solution (ethanol was dissolved in 150 mM hydrochloric acid). Intragastric administration of SD rats with 200 mg/kg of Dendrobium officinale for two weeks decreased gastric secretion, IL-6 and TNF-cytokine levels compared with the lower dose groups and the control groups. This concentration (200 mg/kg) had the strongest inhibitory effect of gastric injury (76.6% inhibition of gastric injury rate) [75]. After the successful establishment of the irritable gastric ulcer model (induced by cold water immersion) and chemical gastric ulcer model (indometacin-induced, 40 mg/kg, gavage) the ulcer index was calculated by Guth standard scoring method. Freshly squeezed Dendrobium officinale juice (containing crude drugs 0.5, 2 g/kg) showed significant declining irritable and chemical gastric ulcer model ulcer indexes ( < 0.01) [76]. However, gastric ulcer is a chronic disease, the security of long-term administration of Dendrobium officinale still uncertain.

Others.
It is found that Dendrobium officinale had hypolipidemic and hypotensive effects. The fine powder solution of Dendrobium officinale (1.5, 3 g/kg) can reduce the levels of TG, TCHOL, and LDL-C in serum significantly and reduce the expression of TNF-and IL-6 in ApoE −/− mice. In addition, it could reduce areas of atheromatous plaque in aortic valve and arch in ApoE −/− mice and then decrease the expression of TNF-and IL-6 in aortic arch [77]. Research showed that stroke-prone spontaneously hypertensive (SHRsp) rats' living days and survival rates were extended by DOP, and hypotensive effect of DOP was significantly better than the nonpolysaccharide ingredients of Dendrobium officinale [78].
Moreover, Dendrobium officinale was used to treat Sjögren's syndrome (SS) with dry eyes and mouth due to impaired lacrimal and salivary glands [80]. Research showed that DOP could suppress the progressive lymphocytes infiltration and apoptosis and balance the disorders of proinflammatory cytokines in the submandibular gland (SG) in vivo. Further, DOP ameliorated the abnormalities of aquaporin-5 (AQP-5) that was supported by in vitro study on A-253 cell line and maintained its function of saliva secretion [79].
Meanwhile, research showed that the DOP group demonstrated higher average scores and an improved average quality of hair growth of C57BL/6J mice (5.0 g/L, the solution was ultra-pure water, each 0.2 mL, smeared for 21 d), compared with the control group. Besides, DOP significantly increased HaCaT cells survival rate and the VEGF mRNA expression levels compared with the control group [80].
Besides, the Dendrobium officinale had an obvious effect on the molecular diversity of intestinal Lactobacillus in mice model (irregular diet for 8 d after gavage of folium senna water decoction for 7 d) with constipation resulting from spleen deficiency (TCM syndrome type) [81]. Dendrobium officinale also can regulate the digestive function in carboninduced constipated mice models [83].

The Toxicology of Dendrobium officinale
After acute toxicity test, genetic toxicity test (Ames test, micronucleus test of bone marrow, and sperm shape abnormality test in mice) and 90-day feeding test in rats, the results showed that protocorms of Dendrobium officinale were without toxicity, genetic toxicity and mutagenicity within the scope of the test dose [84]. Furthermore, the 15% decoction of Dendrobium officinale was used for mice sperm malformation test, Ames test, and micronucleus test of bone marrow in mice, and all test results were negative. In addition, the acute oral toxicity test showed that the highest dose was 10 g/kg b.w. which belonged to the actual nontoxic category [85]. However, in the pesticide safety aspect, the Dendrobium officinale still need more stringent quality control [86].

The Industrialization of Dendrobium officinale
Due to the special trophic mode, seed germination of Dendrobium officinale needs the root symbiotic bacteria [87,88]; the reproduction of wild Dendrobium officinale is limited with low natural reproductive rates. The past three decades witnessed excess herb-gathering of Dendrobium officinale destroying much of the wild habitat resource in China [89]. In 1987, Dendrobium officinale was on the list of national thirdlevel rare and endangered plants [90]. However, artificial cultivation based on tissue culture technology significantly prompted the yield of Dendrobium officinale.
Recently, increased awareness of the tonic therapeutic effect of Dendrobium officinale has increased the demand and as a consequence the price [91]. However, the high-profit margin of Dendrobium officinale has already led to an increase in the market for counterfeits and adulterants [92] mainly by other confusable species of Dendrobium [91]. The appearance of Dendrobium officinale and other species of Dendrobium is very similar, especially after processing into "tiepifengdou"; it is difficult to distinguish them through morphological identification [93]. It is apparent that Dendrobium officinale germplasm resources' separation and purification determine its characters and quality [94]. In terms of microscopic identification, Dendrobium officinale could be identified by vascular bundle sheath observed under the fluorescence microscopy and the distribution of raphides under normal light microscopy [95]. In addition, the taxonomy, phylogeny, and breeding of Dendrobium species have made great progress as the advance of molecular markers in the past two decades [96].
Under such circumstances, pharmacognosy [97], DNA molecule marker technologies including Amplified Fragment Length Polymorphism (AFLP) [98], Inter Simple Sequence Repeat (ISSR) [99], Start codon targeted (SCoT) and target region amplification polymorphism (TRAP) [100], and sequence related amplified polymorphism (SRAP) analysis [101], and so on have been applied to identify Dendrobium  officinale from other Dendrobium species. Further, Yunnan province has completed Dendrobium officinale fine gene map and found more than 48,200 protein-coding genes [102]. Therefore, the identification of Dendrobium officinale is more precise due to the gene technology, but genetic fingerprints are difficult to evaluate the quality, so the gene technology combining with the physical and chemical identification is necessary.
In recent years, the development of Dendrobium officinale health care products is promising [15]. Many related patented products are being registered or have been authorized, including Dendrobium officinale ingredients such as antiaging compounds [103], lactobacillus drink [104], antiasthenopia eye ointment [105], immunoenhancement compounds [106], hypotensive extractive [107], and hypoglycemic and hypolipidemic compounds [108]. Some of these patents have been put into production like "tiepifengdou," one of the most famous processed products of Dendrobium officinale [101]. However, there are few medicines of Dendrobium officinale [109] besides tiepishihu of Chinese materia medica in TCM.
In summary, the TCM theory and ethnopharmacology could inspire modern researches committed to yield and quality control of Dendrobium officinale, while some standards or laws (such as ISO/TC 249 and CITES) regulated artificial cultivation and protected wildlife resources. Finally, industrialization will drive further researches and is conducive to develop deep-processing products, especially the insufficient new drugs, which will also promote the industrialization and form a virtuous circle simultaneously ( Figure 3).

Conclusion
Dendrobium officinale, one of the most famous species of Dendrobium, has long been regarded as precious herbs and health foods applied in TCM and in folk. In this paper, the ethnopharmacology, phytochemistry, pharmacology, and industrialization of Dendrobium officinale were summarized. In recent years, the interest of exploring ethnopharmacologybased bioactive constituents of Dendrobium officinale has increased considerably. Rapid propagation technology has gradually matured, so yield is no longer the bottleneck of Dendrobium officinale development. In addition, the confusable identification and uneven quality still exist, and better quality control standards under modern researches are necessary.
Consequently, the following points deserve further investigation. (1) Polysaccharides are the main composition in Dendrobium officinale with numerous pharmacological researches, but investigation related to its structure-activity relationships remains scant. (2) The pharmacological effects of Dendrobium officinale crude extract and polysaccharide were similar, indicating whether other active ingredients were lost during extraction. (3) There is no enough systemic data about toxicology of Dendrobium officinale. (4) How does TCM theory play a role in Dendrobium officinale further indepth development as theoretical guidance and inspiration source.
Over all, further studies at the molecular level are needed to promote the exploration of chemical compositions and pharmacological mechanisms. In addition, the industrialization of Dendrobium officinale not only protected the germplasm resources but also attracted a large quantity of researches in China, which makes the innovation of Dendrobium officinale novel drug and product a promising prospect.