Phytochemistry, Pharmacology and Traditional Uses of Plants from the Genus Trachelospermum L.

This paper is intended to review advances in the botanical, phytochemical, traditional uses and pharmacological studies of the genus Trachelospermum. Until now, 138 chemical constituents have been isolated and characterized from these plants, particularly from T. asiaticum and T. jasminoides. Among these compounds, lignans, triterpenoids, and flavonoids are the major bioactive constituents. Studies have shown that plants from the genus Trachelospermum exhibit an extensive range of pharmacological properties both in vivo and in vitro, including anti-inflammatory, analgesic, antitumor, antiviral and antibacterial activities. In Traditional Chinese Medicine (TCM) culture, drugs that include T. jasminoides stems have been used to cure rheumatism, gonarthritis, backache and pharyngitis, although there are few reports concerning the clinical use and toxicity of these plants. Further attention should be paid to gathering information about their toxicology data, quality-control measures, and the clinical value of the active compounds from genus Trachelospermum.


Introduction
The genus Trachelospermum L., a member of the dobane family Apocynaceae and first described as a genus in 1851, is widely distributed in Asia and is particularly native to the subtropical regions . The general name of the genus is Caulis Trachelospermi. Trachelospermum is also called as "Luoshi/ 络石 (in Chinese)", "rakusekito (u)/らくせきとう (in Japanese)", "ᄂ ᅡ ᆨᄉ ᅥ ᆨᄃ ᅳ ᆼ (in Korean)". The genus contains about 30 species, mainly distributed in tropical and subtropical zones. Ten species and six variant species are widespread in several provinces in China, especially the East and the Central South of China. The dried leaves and stems of the genus plants can be used as medicine. The stems of Trachelospermum plants have been used as local and traditional medicine in China, Japan and Korea, etc. (https://en.wikipedia.org/wiki/Trachelospermum). The species T. jasminoides and T. asiaticum are important medicinal sources. The dried stem part of T. jasminoides is recorded in various versions of Chinese Pharmacopoeia and is also used as a herbal medicine in Korea and Japan. In Traditional Chinese Medicine (TCM), the dried stem of T. jasminoides is used alone or mixed with other herbs for the treatment of rheumatism, blood cooling, gonarthritis, backache, pharyngitis and bruises diseases. The existing literature demonstrates that the therapy with the medicine is safe and effective both internally and externally. Plants of the genus Trachelospermum are enriched in multiple structurally bruises diseases. The existing literature demonstrates that the therapy with the medicine is safe and effective both internally and externally. Plants of the genus Trachelospermum are enriched in multiple structurally diverse and biologically important lignans [1] and their glycosides, as well as triterpenoids [2] and flavonoids [3]. Modern pharmacognosy and pharmacology have revealed that lignans have strong antitumor activites [4]. To date, there are no published comprehensive reviews on the phytochemistry, traditional uses, pharmacology and toxicological information of plants from genus Trachelospermum. In this review, we summarize the progress on phytochemical studies over the past decades, with all the elucidated compounds listed. The biological characterization of the extracts or components isolated from this genus are also discussed. We believe this paper will be a guide for the full utilization of Trachelospermum plants for new drug development and pharmaceutical applications.

Botany
The genus Trachelospermum belongs to the family Apocynaceae ( Figure 1). Trachelospermum plants pertain to lianas, which usually grow to a height of 10 m. The lianas are woody, stems are brownish and lenticellate, and leaves are blade ovate or narrowly elliptic. The petiole grows from 2 to 12 mm long. The flowers are normally white or purplish, 5-merous, with the small and deeply divided calyx, and 5-10 basal glands inside, apices are usually denticulate. The flowering stages range from March to July, and the fruit phases are normally from July to December [5].

Lignans
Lignans are the representative and predominated type of compounds from the genus Trachelospermum, and are valuable resources for drug design. So far, 33 lignans have been isolated from Trachelospermum plants. In this cluster, dibenzyltyrolactones are the principal compounds, while dibenzylbutane (compounds 1, 21, 26) and arylnaphthalene (compound 12) lignans have been isolated as well. Therefore, according to the Chinese Pharmacopoeia, tracheloside (3) is a quality control standard for the genus Trachelospermum plants, and it is also an active constituent with antitumor [4], anti-estrogenic [1], and α-glucosidase inhibitory activities [48], among others. Besides, other active compounds including arctiin (2), trachelogenin (9) and arctigenin (16) are also widely researched (Figure 7).

Lignans
Lignans are the representative and predominated type of compounds from the genus Trachelospermum, and are valuable resources for drug design. So far, 33 lignans have been isolated from Trachelospermum plants. In this cluster, dibenzyltyrolactones are the principal compounds, while dibenzylbutane (compounds 1, 21, 26) and arylnaphthalene (compound 12) lignans have been isolated as well. Therefore, according to the Chinese Pharmacopoeia, tracheloside (3) is a quality control standard for the genus Trachelospermum plants, and it is also an active constituent with antitumor [4], anti-estrogenic [1], and α-glucosidase inhibitory activities [48], among others. Besides, other active compounds including arctiin (2), trachelogenin (9) and arctigenin (16) are also widely researched (Figure 7).

Lignans
Lignans are the representative and predominated type of compounds from the genus Trachelospermum, and are valuable resources for drug design. So far, 33 lignans have been isolated from Trachelospermum plants. In this cluster, dibenzyltyrolactones are the principal compounds, while dibenzylbutane (compounds 1, 21, 26) and arylnaphthalene (compound 12) lignans have been isolated as well. Therefore, according to the Chinese Pharmacopoeia, tracheloside (3) is a quality control standard for the genus Trachelospermum plants, and it is also an active constituent with antitumor [4], anti-estrogenic [1], and α-glucosidase inhibitory activities [48], among others. Besides, other active compounds including arctiin (2), trachelogenin (9) and arctigenin (16) are also widely researched (Figure 7).

Alkaloids
Alkaloids are less widespread in Trachelospermum plants. Up to now, only nine of this class of compounds have been isolated from T. jasminoides, with skeletons of the monoterpenoid indole type. Bioactivity research on Trachelospermum alkaloids is still rare [43,44].

Traditional Uses
Because of their versatile biological and pharmacological activities, Trachelospermum plants have been traditionally used for the treatment of rheumatism, blood cooling, gonarthritis, backache, pharyngitis and bruises. In TCM culture, T. jasminoide is dewcribed as bitter in taste, a little cold in nature and attributive to the liver and kidney meridians [50]. The traditional method of T. jasminoide consumption is usually decocting with water or wine. Studies on the side effects and safety evaluations of T. jasminoide are limited, although it is widely used in TCM. The Chinese Pharmacopoeia recommends a dose of 6-12 g for T. jasminoide [50].
T. jasminoide was listed for medicinal uses firstly in "Sheng Nong s herbal classic (神农本草经)" during the Han Dynasty more than one thousand years ago. According to "Ben Cao Gang Mu (本草纲目)" (Ming Dynasty), the effect of T. jasminoide is mild, and the main function of T. jasminoide is to treat swelling and pain of bones and joints. Based on "De Pei Ben Cao (得配本草)" (Qing Dynasty), T. jasminoide is used to treat sore throat combined with Belamcanda chinensis and Gardenia jasminoides. Moreover, T. jasminoide can be used combined with Radix Ginseng, Wolfiporia cocos to treat turbid urine. In addition, T. jasminoide can treat tuberculosis, snake venom and haemorrhage with the combination of Melastoma dodecandrum, accordance with "Jiang Xi Cao Yao (江西草药)". T. jasminoide is used to make wine containing several vine plants including Piper kadsura, Spatholobus suberectus, Acanthopanar gracilistµlus, Taxillus sutchuenensis and Chaenomeles sinensis to resist rheumatism and arthritis.
The preparations related to Trachelospermum recorded in the Chinese Pharmacopoeia are She Xiang Kang Shuan capsule and Zhong Feng Hui Chun pill, both of which are used for the treatment of dizziness, numbness and hemiparalysis caused by stroke [50].

Pharmacology
In recent years, the pharmacological activities of Trachelospermum have attracted attention. Modern research has shown that Trachelospermum plants play a role in anti-inflammatory and analgesic, antitumor and antiviral effects, although other pharmacology activities also have been documented.

Anti-inflammatory and Analgesic Activity
Plants in the genus Trachelospermum, especially T. jasminoides and T. asiaticum, have a long history of use in China as anti-rheumatic agents and for the treatment of arthritis-related diseases. In agreement with the traditional usage of plants from the genus Trachelospermum, several studies have illustrated that plants in this genus possess anti-inflammatory and analgesic effects both in vitro and in vivo. In 2003, ethanol extracts from several vine plants (Spatholobus suberectus, Tripterygium wilfordii, Sinomenium acutum, Piper kadsura, T. jasminoides, etc.) used in TCM to treat inflammatory conditions were evaluated against a panel of key enzymes relating to inflammation. The anti-inflammatory abilities against enzymes such as cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2), phospholipase A2 (PLA 2 ), 5-lipoxygenase (5-LO) and 12-lipoxygenase (12-LO) were estimated. Among vine plants, T. jasminoides extract (extract/herbs = 0.85 g/30 g) exhibited significant anti-inflammatory ability against COX-1, COX-2, PLA 2 and 12-LO with the IC 50 values of 35, 138, 33 and 29 µg/mL respectively [51], which implied that T. jasminoides could prevent the generation of inflammatory mediators from arachidonic acid metabolism. Besides, the extract restrained the LPS-induced expression of inducible nitric oxide synthase (iNOS) protein and tumor necrosis factor-α (TNF-α) in RAW 264.7 cells in a dose-dependent manner (30-300 mg/mL) [52]. Meanwhile, the activating phosphorylations of p38 MAP kinase and NF-kB were inhibited by the extract in a dose-dependent manner, which were important for iNOS expression and NO production. Flavonoids were supposed to be contributors to the inflammatory effects of WET according to the HPLC analysis [3]. Compound 2 was identified by HPLC analysis and suggested to be the effective compound through exoteric experiments. Compound 35 isolated from the ethanol extract of T. jasminoides [53] was reported to be effective in reducing nitric oxide (NO) production in LPS-induced RAW 264.7 cells, in which inflammatory elements including TNF-α and interleukin 1β (IL-1β) were inhibited (inhibition values 23.3% and 64.1%).
In vivo, at a dose of 400 mg/kg, the T. jasminoides extract inhibited 12-O-tetradecanoylphorbol 13-acetate-induced mouse ear oedema, arachidonic acid-induced mouse ear oedema and acetic acid-induced writhing with the inhibition ratio of 65.7% and 61.8% inhibition ratio for oedema thickness and 45.8% inhibitory value for the writhing responses. The extract suppressed carrageenan-induced oedema in a dose-dependent and time-dependent manner in rats compared with the control groups [52].
Water extract of T. jasminoides (WET) showed antinociceptive effects in an acetic acid-induced writhing model, formalin test and carrageenan-induced edema. At a dose of 0.5 g/kg, WET performed markedly activity compared with control. Moreover, WET had significant inhibitory effects on TNF-α level, MDA level and activities of antioxidant enzymes such as SOD, glutathione peroxidase (GPx) and glutathione reductase (GRx) [3].
In the mouse model of type II collagen-induced arthritis (CIA), the mixture of ethanol extracts of Trachelospermi caulis and Moutan cortex radicis (TCMC) ameliorated histological deformation of joints and serum levels of rheumatoid arthritis biomarkers, such as cartilage oligomeric matrix protein, serum amyloid P and anti-collagen typeII IgG antibody. Additionally, TCMC suppressed pro-inflammatory cytokines (TNF-α, IL-1β and IL-6) and chemokines (macrophage inflammatory protein-1, monocyte chemoattractant protein-1) in CIA mice. Therefore TCMC repress the production of various inflammatory factors and the formation of osteoclasts through the inhibition of NF-kB and AP-1 activation [54].

Antitumor Activity
A herbal analgesic gel named Tong-Luo-San-Jie (TLSJ), was reported to be effective for alleviating bone cancer pain in rats. TLSJ is composed of ethanol extracts form the herbs T. jasminoides, Piper kadsura, Dioscorea nipponica, Corydalis yanhuso, etc. Walker 256 rat carcinoma cells were inoculated into Sprague-Dawley rats, then TLSJ was administered for 21 days. TLSJ treatment significantly restored bone cancer-induced decrease of paw withdrawal latency and mechanical threshold compared to inert gel. Meanwhile, it decreased the level of carboxyterminal pyridinoline cross-linked type I collagen telopeptides, bone-specific alkaline phosphatase and inhibited osteoclast activities in blood serum [55]. Furthermore, TLSJ was deemed valid in alleviating bone cancer-induced mechanical allodynia and thermal hyperalgesia by downregulating transient receptor potential channel expression in lumbar dorsal root ganglia and lumbar spinal cord interleukin-17A (IL-17A) in spinal astrocytes [56].
Moreover, the cytotoxic activity compounds 7, 9 and 16 were evaluated a1gainst human pancreatic cancer PANC-1 cells in nutrient-deprived medium. These compounds which have the (2R,3R)-absolute configuration exhibited preferential cytotoxicity compared with other lignan compounds in a concentration-dependent manner, with PC 50 values of 0.54, 6.82 and 5.85 µM, respectively [58]. Compound 111, a new isoflavonoid glycoside, was isolated from the ethyl acetate extract of T. jasminoides, which was found to have the inhibitory activity against HepG2 and HL-60 cancer cells with IC 50 values of 131.5 and 58.2 µM, respectively [42].

Antiviral Activity
The inhibition of HIV-1 viral enzymes such as reverse transcriptase, HIV-1 protease andα-glucosidase were assessed using 18 herb extracts. Among these extracts, water extract and methanol extract of T. asiaticum showed weak inhibitive activity against HIV-1 protease, with the inhibition rate being 23.4% and 23.1% on the concentration of 100 µg/mL, respectively [59]. The ethanol extract of T. jasminoides and T. liukiuense showed weak anti-proliferative effect against T-cell lymphotropic virus type I (HTLV-I) in HTLV-I-infected T-cell lines. Extracts from T. jasminoides exhibited activities against MT-1 and MT-2 cells (EC 50 values 10-100 µg/mL), while T. liukiuense only exhibited activity against MT-2 cells [60]. As for the effective ingredient, compound 9 isolated from T. jasminoides was recognised as a potential inhibitor of hepatitis C virus through interfering with the interactions between HCV glycoprotein E2 and the host entry factor CD81. Compound 9 inhibited cell culture-derived HCV and HCV pseudo-particles with the IC 50 of 0.325 and 0.259 µg/mL [61].

Antibacterial Activity
The essential oil compositions of T. jasminoides obtained from Chiang Ra and Chiang Mai city were identified by GC-MS (Agilent Technologies, Palo Alto, CA, USA) analysis. More than 90 kinds of constituents were identified, with E-nerolidol, α-phellandrene (from Chiang Rai) and trans-linalool (from Chiang Mai) being the major components of the essential oil. The antibacterial activities of the essential oils were determined against Gram-negative and Gram-positive bacteria and minimum inhibitory concentration (MIC) values were evaluated. Essential oils from Chiang Rai showed a higher diameter of inhibition than that acquired form Chiang Mai, with the lowest MIC values against E. aerogens and P. aeruginosa are 7.81 (Chiang Rai) and 15.62 (Chiang Mai), respectively. Constituents from the essential oil such as E-nerolidol as α-phellandrene have been reported to exhibit antibacterial activity [49].

Other Biological Activities
In modern research, Trachelospermum plants were reported to have a variety of activities besides the abovementioned fields. Ethanol extract of T. asiaticum was considered to be effective on intestinal barrier function in intestinal epithelial cells. In a model of monolayers of intestinal epithelial cells (Caco-2), chloroform and ethyl acetate fractions promoted transepithelial electrical resistance (TEER) values and decreased quantity of permeated ovalbumin (OVA) flux. Compounds 3 and 9 were identified as the active constituents of this intestinal barrier function by HPLC analysis [62].

Conclusions
This review presents a comprehensive summary of the botany, phytochemistry, traditional uses and pharmacology of the genus Trachelospermum. To date, 138 compounds from Trachelospermum were characterized, and lignans, triterpenoids and flavonoids are the main compounds. The reports on the bioactivities of extraction and compounds from Trachelospermum are chronicled. Research on bioactive components are concentrated in lignans and flavonoids, which may contribute either directly or indirectly to the biological effects of the Trachelospermum genus.
There are multiple Trachelospermum species in the genus, with T. jasminoides and T. asiaticum being the two species that have received most attention due to their important medicinal value. Studies implemented through in vivo and in vitro experiments have demonstrated the bioactivities of Trachelospermum plants, most of which support their traditional medicine uses. Pharmacology studies are mainly focused on the anti-inflammatory and analgesic, antitumor and antiviral activity, and some preparations containing T. jasminoides have been developed into novel agents to prevent stroke and rheumatoid arthritis. However, the pharmacological effects of only a few components, such as compounds 3, 7, 9, etc. have been studied. Precise investigations of the chemical composition of popular drugs are needed, as well as studies on the possible mechanism of action of the bioactive compounds and their structure-function relationships. Information on toxicity evaluations and randomized clinical trials for the genus Trachelospermum plant is very limited, although this plant is frequently used in TCM. Thus, further investigations on the toxicity, effective ingredients and clinical studies of species of the genus Trachelospermum are urgently needed to meet the requirements of evidence-based medicine.