Advances in Chemical Constituents and Pharmacological Activity of Pholidota spp.

Xiucai WU, Shuang LIANG, Zhengying SU

College of Pharmacy, Guangxi University of Chinese Medicine, Nanning 530200, China

Abstract In recent years, a large number of studies have shown that the effective compounds extracted from Pholidota spp. have pharmacological activities such as anesthesia, analgesia, anti-fatigue, anti-hypoxia, anti-tumor and anti-oxidant. Because of significant activity and small side effects, Pholidota spp. have attracted much attention. In this article, the effective chemical constituents and pharmacological activity of Pholidota spp. are reviewed comprehensively in order to provide reference for the further rational development of Pholidota spp. and development of new drugs.

Key words Pholidota spp., Medicinal plant, Chemical constituent, Pharmacological activity

1 Introduction

Pholidotasp. (Orchidaceae) is a perennial epiphyte. It is widely distributed in China, mainly in high-altitude jungles and rocks in Zhejiang, Guangxi, Jiangxi, Fujian and Taiwan, China.Pholidotaspp. are a class of Chinese herbal medicines with a long history of medicinal use. Their medicinal use is recorded inEssentialsoftheMedicinalNatureofRawHerbs, with pseudobulb or whole grass as medicine.Pholidotaspp. are sweet and slightly bitter in taste, and cold in nature, with functions of nourishing Yin, moistening lung, clearing heat, cooling blood, purging fire, detoxifying, drying dampness, relieving itching and diminishing swelling. In clinics,Pholidotaspp. are used to treat dizziness, headache, cough, hematemesis, nocturnal emission, dysentery, leucorrhea and infantile malnutrition. The chemical composition ofPholidotaspp. is complex. The compounds that have been successfully separated and identified include flavonoids, phenanthrenes, phenols, terpenes, steroids, polysaccharides, aliphatics and minerals. Different chemical ingredients show different pharmacological activities, such as anesthesia, analgesia, inhibiting central nervous system, anti-fatigue and anti-hypoxia[1-2].Pholidotaspp. are important Chinese medicinal materials. They have great application prospects in the treatment of diseases and have high scientific research value and medicinal value. In this article, the progress in the research on chemical constituents and pharmacological activities ofPholidotaspp. is introduced briefly, to provide a reference for the further reasonable development ofPholidotaspp. and development of new drugs.

2 Chemical composition

According to related literature reports, the compounds isolated fromPholidotaspp. are diverse, and there are about 72 kinds of compounds, including flavonoids, polysaccharides, terpenes, phenols, aliphatics, phenanthrenes,etc[3-4]. However, the distribution of compounds in different parts ofPholidotaspp. is different. Shen Zonggenetal.[5]detected the infrared spectra of the extracts of leaves, roots, bulbs and rhizome ofPholidotacantonensisRolfe. It was found that the infrared spectra of extracts of different parts have differences in waveform and spectral absorption intensity, which was mainly due to the inconsistent content of compounds contained in specific parts and the interference of other compounds. In addition, crude extracts ofPholidotaspp. obtained by different extraction processes also show different pharmacological activities[6].

2.1FlavonoidsFlavonoids have high contents inPholidotaspp. Common extraction solvents include ethyl acetate, petroleum ether, n-butanol and ethanol. Li Peiyuanetal. extracted flavonoids fromP.cantonensisRolfe. with different solvents. The results show that the content of flavonoids extracted with ethyl acetate was 39.6 mg/g, and that extracted with petroleum ether was only 10.6 mg/g[2, 7]. There are various types of flavonoid monomers inP.cantonensisRolfe. This may be because that different monomers have different polarities, leading to different extraction effects between different solvents. Chen Xiaobingetal.[3]submitted the powder ofP.cantonensisRolfe. to repeated extraction and concentration, adsorption with macroporous adsorption resin, elution with water and 10%, 40% and 80% ethanol solutions for chromatographic separation, thin-layer chromatography, combination of similar fractions, repeated silica-gel column chromatography, crystallization separation and repeated recrystallization, and three flavonoid compounds were finally obtained: 7-hydroxy-3-(4′-hydroxyphenyl) isoflavone, quercetin, 7-hydroxy-3-(4′-methoxyphenyl) chromone.

2.2PolysaccharidesSo far, domestic and foreign researchers have focused on the pharmacological activity of polysaccharides fromPholidotaspp., but there are few studies on their physical and chemical properties. A research team of Fujian Agriculture and Forestry University has carried out a systematic study on the physical and chemical properties of polysaccharides fromPholidotaspp. The monosaccharides inPholidotaspp. include xylose, mannose, glucose and galactose, of which the molar ratio is 13.33: 24.13: 5.59: 3.10. The connection methods between the monosaccharides include 1→6 connection, 1→2 connection and 1→3 connection. Among them, 1→2 connection is dominant. The side chain groups of polysaccharides fromPholidotaspp.Pholidotaspp. have no carboxyl structure. They have a maximum absorption peak at 490 nm. The average molecular weight is 45 200 D. The intrinsic viscosity is 1.55 mL/g[8-9].

The most commonly used method for the extraction of polysaccharides fromPholidotaspp. is water extraction. Yang Haihuaetal.[4]investigated the effects of solid to liquid ratio, extraction time and extraction temperature on the extraction rate of polysaccharides fromPholidotaspp. using single-factor tests and L9(34) orthogonal test, to determine the optimal extraction process of polysaccharides fromPholidotaspp. After protein removal by salting-out method and repeated precipitation with ethanol, water extract ofPholidotasp. with a total polysaccharide content of 3.352% was obtained. Tian Chaoetal.[9]significantly improved the extraction effect of polysaccharides fromPholidotasp. by assisting certain physical conditions, such as heating extraction and ultrasonic extraction, and the total concentration of polysaccharides in the water extract was up to 14.01%.

2.3TerpenoidsAccording to research reports at home and abroad, there are 15 terpenoids that have been isolated and identified from the whole plant ofPholidotaspp. Most of them are triterpenoids, and monoterpenoids have not been reported. For the first time, researchers in China have isolated three triterpenoids fromPholidotasp., including cyclophlidone, cyclopholidonol and 25-methylene cycloartanyl p-hydroxy-trans-cinnamate[10]. Zhi MBetal.[11]isolated triterpenoids, pholidotine A and pholidotine B, fromPholidotayunnanensisRolfe. Li B[12]isolated triterpenoids, 24-methylenepollinastanone and 24-methylenecycloartan-3-one, fromP.cantonensisRolfe. Other triterpenoids identified include 24-methylenecycoartanol[4], hop-22 (29) -ene[12], cycloeucalenol[13], cycloneolitsol[14], pholidotin and 24-methylidenecycloartan-3-yl (E) -p-hydroxycinnamate[15]. At present, there are only two diterpenoids that have been isolated fromP.cantonensisRolfe., clerodane and labdane[12].

Among the terpenoids isolated, 7 of them derive fromP.cantonensisRolfe. (including two diterpenoids), accounting for nearly half of the total. It can be seen that terpenoids inP.cantonensisRolfe. are relatively abundant amongPholidotaspp.

2.49,10-dihydrophenanthrenesThe proportion of 9,10-dihydrophenanthrenes in the volatile chemical constituents ofPholidotaspp. is 3.78%[16]. Although the content is not high, these constituents are unique inPholidotaspp[17-19]. Therefore, they can be used as a potential physical and chemical index to identify the relationships betweenPholidotaspp. Another important feature of 9,10-dihydrophenanthrenes is that the side chains often carry multiple phenolic hydroxyl groups, which endow them with strong antioxidant activity. Therefore, in the development of antioxidants, 9,10-dihydrophenanthrenes have broad prospects.

At present, there are 27 9,10-dihydrophenanthrene monomers isolated fromPholidotaspp. FromP.cantonensisRolfe., ephemeranthoquinone and orchinol have been isolated[20]; fromPholidotaarticulate, flavidin, isofavidinin and iso-oxoflavidinin have been isolated[21]; fromP.yunnanensisRolfe., 13 compounds have been isolated: lusianthridin, eulophiol, densiflorol B[22], coelonin[23], 2,4,7-tyihydroxy-9,10-dihydrophenanthrene, phoyunnanins A, phoyunanins B, phoyunnanins C, imbricatin, 4,4′,7,7′-tetrahydroxy-2,2-dimethoxy-9,9′,10,10′-tetrahydro-1,1′-biphenanthrene[17], phoyunnanins D, phoyunnanins E[15]and pholidotol[23]; and fromPholidotachinensisLindl., 11 compounds have been isolated: eulophiol, coelonin, lusianthridin, hircinol, cannabidihydrophenanthrene, erianthridin, 2,4,7-tyihydroxy-9,10-dihydrophenanthrene, phoyunnanin D, flavanthrin, blestrianin A[18]and 4,5-dihydroxy-2-methoxy-9,10-dilydrophenan[24].

3 Main pharmacological activities

3.1AnesthesiaShu Wenhai[25]performed local anesthesia experiments with three kinds of animals. It was found that the water extract ofPholidotasp. had local anesthetic effect. The water extract ofP.cantonensisRolfe. could block action potential of neural stem in toad, and the effect was similar to that of procaine. The water extract ofP.cantonensisRolfe. also had an anesthetic effect on the corneal surface of rabbit, and the effect was similar to that of dicaine. The 100% water extract was injected intradermally into guinea pig to test its pain response, and the positive rate of pain response was recorded. The results show that the water extract ofP.cantonensisRolfe. had the effect of infiltration and anesthesia.

3.2AnalgesiaLiu Jianxinetal.[26]found that the water extract ofPholidotasp. significantly inhibited the writhing response in mice caused by glacial acetic acid by using hot plate method, acetic acid writhing method and electric stimulation pain method, and the results show that the water extract ofPholidotasp. has analgesic effect. Liu Hongxuetal.[27]studied the pharmacologically active part ofP.cantonensisRolfe. It was found that the water extract ofP.cantonensisRolfe. could significantly increase the pain threshold of mice caused by hot plate and reduce the number of writing in mice induced by glacial acetic acid.

3.3Anti-fatigueandanti-hypoxiaZhou Honglinetal.[28]evaluated the physiological characteristics of mice from five aspects, anti-hypoxia under normal pressure, hypoxia caused by sodium nitrite, specific myocardial hypoxia, anti-ischemic hypoxia and endurance to analyze the anti-fatigue and anti-hypoxia physiological activities of extract ofPholidotasp. After injection of appropriate amount of extract ofPholidotasp., the specific manifestations of mice were tolerance to hypoxia environment, prolonged survival time and prolonged wheezing time under ischemia-hypoxia environment. The research results show that the extract ofPholidotasp. has certain efficiency in anti-fatigue and anti-hypoxia.

3.4Anti-tumorQu Gexiaetal.[29]used thePyriculariaoryzaescreening system and tumor cellinvitrocytotoxic activity screening system for activity tracking, and discussed the possible mechanism with human liver cancer cell line HpeG2. Wang Guanghuietal.[30]combined 50 and 30 g ofP.yunnanensisRolfe. with GP regimen. The results showed that the adjuvant therapy withP.yunnanensisRolfe., on the basis of chemotherapy, improved the clinical symptoms of patients and reduced the toxicity of chemotherapy, and the efficacy was better than that of single chemotherapy.

3.5Anti-cancerThe effects of the chemical constituents ofP.yunnanensisRolfe. of the chloroform layer on the growth of HepG2 cells, cell cycle and expression of cyclins were determined by using thiazolyl blue colorimetry, flow cytometry and protein electrophoresis. The results showed that the chemical constituents ofP.yunnanensisRolfe. of the chloroform layer could block the cell cycle of human liver cancer cell line HepG2. It indicates that chloroform extract ofP.yunnanensisRolfe. has a certain anti-cancer effect[30], but the mechanism of action needs further study.

4 Outlook

P.cantonensisRolfe. has a long history of application. The phenanthrenes, terpenes and polysaccharides contained in the plants are mostly biologically active. The domestic and foreign researches onP.cantonensisRolfe. mainly focused on the extraction and separation of chemical components. The material basis for efficacy and pharmacological action mechanism ofPholidotaspp. have not been clear. Therefore, in the future, the research on the material basis for efficacy and pharmacological action mechanisms ofPholidotaspp. should be further strengthened.