Analysis Of Chemical Constituents in Cistanche Species

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Yong Jiang, Peng-Fei Tu, et al

Abstract

Species of the genus of Cistanche (Rou Cong Rong in Chinese) are perennial parasite herbs and are mainly distributed in arid lands and warm deserts. As a superior tonic for the treatment of kidney deficiency, impotence, female infertility, morbid leucorrhea, profuse metrorrhagia, and senile constipation, Cistanche herbs earned the honor of “Ginseng of the desert”. Recently, there has been increasing scientific attention to Herba Cistanche for its remarkable bioactivities including antioxidation, neuroprotection, and anti-aging. The chemical constituents of Cistanche plants mainly include volatile oils and non-volatile phenylethanoid glycosides (PhGs), iridoids, lignans, alditols, oligosaccharides, and polysaccharides. Pharmacological studies show that PhGs are the main active components for curing kidney deficiency, antioxidation, and neuroprotection; galactitol and oligosaccharides are the representatives for the treatment of senile constipation, while polysaccharides are responsible for improving body immunity. In this paper, the advances on the chemical constituents of Cistanche plants and their corresponding analyses are reviewed.

Keywords: Cistanche Herba, Cistanches Chemical, constituents Analysis, Phenylethanoid glycosides

1. Introduction

Cistanche Hoffmg. Et Link, one of the genera of the Orobanchaceae family, with 22 species in the world, is mainly distributed in the arid lands and deserts in the northern hemisphere, such as Xinjiang, Inner Mongolia, Ningxia autonomous regions, and Gansu, Qinghai provinces of China, as well as Iran, India, Mongolia, etc. [1]. Their growth environments are very severe: extreme arid climate, severe variation of temperatures, intensive sunshine, less than 250 mm of annual precipitation, and depauperate soils [2,3]. The Cistanche species belong to the perennial parasite herbs, which commonly attach onto the roots of sand-fixing plants, such as Haloxylox ammodendron, H. persicum, Kalidium foliated, and Tamarix plants, etc. [3]. There are six Cistanche species in China, according to the record of Taxonomical Index of Chinese Higher Plants [4]. However, a further study confirmed that only four species and one variation of Cistanche exist in China, i.e. Cistanche deserticola Y.C. Ma, C. tubulosa (Schenk) R. Wight, C. salsa (C.A. Mey.) G. Beck, C. salsa var. albiflflora P.F. Tu et Z.C. Lou and C. sinensis G. Beck [5].

Rou Cong Rong (Herba Cistanche), first recorded in Shen Nong’s Chinese Materia Medica, refers to the dried succulent stems of the Cistanche plants. Herba Cistanche has been considered as a superior tonic and earned the honor of “Ginseng of the deserts”. The scientific values of Herba Cistanche lie in the treatment of kidney deficiency, impotence, female infertility, morbid leucorrhea, profusemetrorrhagia, and senile constipation[6,7]. It has been the most frequently prescribed drug against kidney deficiency in China for successive dynasties. Among Cistanche species, only C. deserticola has been reordered in the Chinese Pharmacopoeia (2000 edition) [8], and C. tubulosa was added to the 2005 Chinese Pharmacopoeia as an alternative, for its similar chemical constituents, pharmacological activities, and its relatively affluent resource compared to C. deserticola [9–11]. However, in recent years, the wild C. deserticola is on the edge of extinction due to over-harvesting, and it has been collected as one of the Class II plants needing protection in China. Due to the deficiency of the natural resources of the official Herba Cistanche, other species of this genus, such as C. salsa and C. Sinensis, are also used as substitutes in many areas [10].

Scientific research on Cistanche plants started in the 1980s [12], and the chemical analysis indicated that various compounds, including essential oils, phenylethanoid glycosides (PhGs), iridoids, lignans, alditols, oligosaccharides, and polysaccharides are the main constitutes of Cistanche plants [13,14]. Pharmacological research showed that the extracts from Cistanche plants possess a wide spectrum of activities, such as curing kidney deficiency and senile constipation, advancing the ability to learn and memorize, treating Alzheimer’s disease, enhancing immunity, anti-aging, and anti-fatigue [14–21]. With the improvement of living standards and the coming of an aging society, Cistanche plants have gained more attention and have been used more and more widely due to their distinguished pharmacological activities.

There have been several reviews on the study of chemical constituents and pharmacological activities of Cistanche plants [13–15]. The present paper focuses on the chemical analysis of this genus and the progress on chemical constituent studies.

2. Volatile compounds

The commonly used extraction methods for the volatile compounds of TCMs include steam distillation and lipophilic organic solvent extraction. Using steam distillation, the essential oils of C. salsa and C. tubulosa were extracted, and 38 and 21 components were identified by GC–MS, respectively (Table 1). The main constituents in the essential oils of C. salsa consist of alkanes, alcohols, aldehydes, and some heterocyclic compounds, while palmitic acid and linoleic acid are the two major constituents of the total oils of C. tubulosa [22,23]. The volatile compounds of C. deserticola were extracted by petroleum ether, and 25 constituents were identified by GC–MS. The three richest constituents are methyl 14-methylpentadecanoate (13.61%), ethyl palmitate (12.39%) and 2,5,6-trimethylolethane (7.60%) [24]. Another report on the volatile components of C. deserticola showed that eugenol was the main component when using a simultaneous distillation-extraction method [25]. The different analytical results of these two papers [24,25] might be caused by different extraction methods and different analytical conditions of GC–MS.

Besides these, Ma reported a supercritical flfluid extraction (SFE) method to extract the non-polar constituents from C. salsa. The analysis of the extract by GC–MS showed some esters and low molecular compounds containing oxygen or nitrogen existing, besides the alkanes. This result demonstrated that more polar compounds could be extracted by SFE through the addition of a polar modifier [26].

3. Non-volatile compounds

The non-volatile compounds of Cistanche plants mainly include phenylethanoids, iridoids, lignans, alditols, oligosaccharides, and polysaccharides. Up to now, more than 100 non-volatile compounds have been isolated from Cistanche plant . The distribution of various types of compounds in Cistanche plants is listed in Table 2. In 1995, Moriya [27,28] reported that the plant material of C. salsa had been wrongly identified before when he investigated the sources of Herba Cistanches from the Japanese medical markets, so the chemical constituents isolated from C. salsa in the 80s have been reassigned to C. deserticola in this review.

3.1. Phenylethanoid glycosides

3.1.1. Chemical structures of PhGs

PhGs have been regarded as the major active components of Cistanche species. To date, 34 PhGs (phenylethanoid glycosides) have been isolated from Cistanche plants, including 22 disaccharide glycosides, 10 trisaccharide glycosides, and 2 monosaccharide glycosides (Table 3). By analyzing the structures of PhGs in Cistanche, the following structural characteristics have been summarized: the sugar moiety of disaccharide glycosides consists of glucose and rhamnose, with a Glc (3→1) Rha linkage. The glucose commonly links directly with the aglycone, and in its position of C4 or C6, where a coumaroyl or caffeoyl is usually located. When the PhG is to be a trisaccharide glycoside, additional glucose or rhamnose usually appears at the C6 position of the inside glucose. Among those PhGs (phenylethanoid glycosides) from Cistanche species, crenatoside (34) is an exceptional one, for an ether ring exists between the  position of aglycone and C-2 position of the inside glucose in its structure [34]. Recently, the X-ray single-crystal structure of salidroside (15), a PhG isolated from C. deserticola, has been reported for the first time [44].

The pharmacological activity studies of PhGs (phenylethanoid glycosides) have demonstrated that they have various functions, such as antioxidation, neuroprotection, enhancing immune and sexual function, hepatoprotection, anti-radiation, etc. [15–17,40,48–50]. Among them, neuroprotection is becoming a hot topic. Some single components or fractions of PhGs (phenylethanoid glycosides) have been reported to inhibit the apoptosis of neuronal cells induced by various chemicals [51–57], and their neuroprotection in vitro has also been proved by several animal models in vivo [58–64]. These results indicate that PhGs (phenylethanoid glycosides) could be an attractive candidate for the treatment of neurodegenerative disorders, such as dementia or Parkinson's disease.

3.1.2. Analysis of PhGs

As the major active components in Cistanche plants, PhGs (phenylethanoid glycosides) are usually used as markers for the quality evaluation of crude drugs or their corresponding formulations.

3.1.2.1. Analysis of PhGs by thin-layer chromatography (TLC).

Zhang first established a TLC identification method for acteoside (2), echinacoside (11), and cistanoside A (3) in Herba Cistanches by silica gel, using ethyl acetate–methanol–9% acetic acid (20:3:2) as developing solvent, and FeCl3 solution as coloring reagents [65]. This method was also used in Chinese Pharmacopoeia (2000) for the identification of acteoside (2) [8]. However, in Chinese Pharmacopeia (2005), the adsorbent of thin layer chromatography has been changed from silica gel to polyamide in order to obtain a much better separation effect, and methanol–acetic acid-water (2:1:7) has been used as a developing solvent. Two major PhGs in Herba Cistanches, Echinacoside (11) and acteoside (2) could be simultaneously identified [9].

3.1.2.2. Analysis of PhGs by Ultraviolet Spectrophotometry (UV).

As mentioned above, the cinnamoyl group often exists in the structures of PhGs, thus, PhGs could be determined directly by UV or by the colorimetric method after reacting with some coloring reagents [66–72]. However, as we know that the colorimetric method is not a reasonable approach for the accurate determination of chemical constituents in TCMs, due to its instability, poor reproducibility, and huge testing error. Moreover, it is more tedious to pre-process the samples detected by UV than by the other methods. Thus, now, the UV method is not used for the quantitation of the pure compound anymore, but only for the determination of total PhGsoccasionally.

3.1.2.3. Analysis of PhGs by high-performance liquid chromatography (HPLC). Among all of the analysis methods, HPLC is the most frequently used one for the qualitative and quantitation of PhGs, and Table 4 summarizes the methods published on the analyses of PhGs by HPLC in literature, which will be detailed as follows.

3.1.2.3.1. Analysis of PhGs in crude drugs, biological samples, and complex products by HPLC.

In 1995, Xu performed a comparison of the chemical constituents of C. deserticola with its substitute C. salsa. The HPLC analysis showed that the chemical composition of PhGs (phenylethanoid glycosides) between these two species was similar, but their quantity was different [73]. In the same year, Moriya made a comparison among the chemical components of C. deserticola (Cd), C. tubulosa (Ct), and C. salsa (Cs), using seven PhGs as markers. The results showed that cistanosides A (3), C (5), and a trace amount of tubuloside A (17) existed in Cd and Cs, whereas only tubuloside A (17) existed in Ct, without cistanosides A (3) and C (5). Also, the total amounts of PhGs in Ct and Cs plants had been found to be more than that in Cd plants [28]. It is valuable that this paper has compared the difference among the Cistanche genus through multi-components analysis; however, it is regretful that the quantitation of these seven PhGs (phenylethanoid glycosides) was performed only by one point external standard method, without a systematic methodology validation.

Tu made a qualitative analysis of six PhGs (phenylethanoid glycosides) and a quantitative analysis of two PhGs in the Cistanche genus by Rp-HPLC. The results showed that the chemical constituents of C. deserticola, C. salsa, C. salsa var. albiflflora, and C. tubulosa were similar, while those of C. Sinensis were different from the others [10]. Wang established a method for the analysis of seven PhGs in C. deserticola, C. tubulosa, and C. salsa with HPLC/MS/MS, and the results showed that the chemical ingredient distribution of the seven references PhGs is different in each species [74]. The fragmentation pathways of the glycosidic linkages, the ester bond, and some interesting neural losses of PhGs were discussed in this paper [74] and in another one [75]. However, the advantage of the HPLC–MS technique has not been demonstrated thoroughly in these analyses, because only the fragmentation mechanism of PhG standards was studied. Adopting these mechanisms to elucidate unknown PhG compounds to give more chemical information, and the fragmentation mechanism study of other skeleton compounds have been neglected.

Besides qualitative analysis, there are also many reports on the quantitative analysis of Herba Cistanches, especially of two major PhGs (phenylethanoid glycosides), echinacoside (11) and acteoside (2). In 2000, Zhang established a quality standard for C. deserticola, including the content determination of acteoside (2) by HPLC, combined with the qualitative identification of fifive components by TLC [65]. In 2003, an Rp-HPLC method for the detection of echinacoside (11) and acteoside (2) in Herba Cistanches cultivated on different host plants and habitats was established. The author used two different mobile phases for the determination of echinacoside (11) and acteoside (2), i.e. acetonitrile-water–glacial acetic acid (13:86:1) for echinacoside and methanol-water–glacial acetic acid (32:67:1) for acteoside. The preliminary result showed that the contents of echinacoside and acteoside were obviously influenced by different hosts, and the contents of these two compounds in C. tubulosa hosted in cultivated Tamalrix L. were the highest [76].

Considering that it is a little tedious to determine two constituents in the same plant using two different solvents, a simpler Rp-HPLC method was established for simultaneous detection of echinacoside (11) and acteoside (2) [77]. Chen then adopted this method to determine the contents of echinacoside (11) and acteoside (2) in the wild and cultivated C. tubulosa [78]. The results showed that the content of echinacoside (11) was markedly higher than that of acteoside (2) in all the samples, and the content of these two active components in wild was higher than that in cultivated [78]. It deserves to mention that the sample preparation in this paper adopted the method of mixing multi-batches together, which means that the author has considered the obvious individual quality differences in Herba Cistanches.

Since the wild Cistanche species are on the edge of extinction, the planting of C. deserticola and C. tubulosa is being carried out in Xinjiang and Inner Mongolia, China. In order to give some theoretical guidance for the cultivation, different cultivated samples have been analyzed. Cao determined the content of PhGs (phenylethanoid glycosides) in spring and autumn with LC-MS, in order to compare C. deserticola samples collected in different seasons. Four PhGs (phenylethanoid glycosides), i.e. echinacoside (11), acteoside (2), cistanoside A (3), and 2 -acetylacteoside (1) were selected as markers, and their total content was observed to be higher in spring than in autumn [79]. Wang made a study on the chemical constituents variation at different growing times and different parts of the cultivated C. tubulosa, using the fingerprint and the content of echinacoside (11) as an index. He found that the chemical distribution of PhGs (phenylethanoid glycosides) was similar among different samples, but the quantity of each PhG, especially of echinacoside (11), was significantly different among various samples. After comparison, he concluded that the cultivating time of C. tubulosa should be over three years, and its harvest time must be controlled strictly before blooming. In this paper, the quality of cultivated plants was found to be no better than wild ones, so the author suggested that the cultivating technology should be promoted to improve the content of active compounds [80]. Yang studied the dry matter accumulation and echinacoside (11) content of C. tubulosa in Huabei plain. The result showed that the dry matter accumulation of C. tubulosa was in the “S”-shaped variant, and the content of echinacoside (11) was the highest when C. tubulosa grew up for 5 months [81].

Other than these, fingerprint, a new technique focusing on the systemic and comprehensive characteristics of the analyzed samples has also been used for the quality evaluation of Cistanche plants. As mentioned above, Wang analyzed the chemical constituents and their variation in cultivated C. tubulosa by using fingerprint and other indicators [80]. Xie established a chromatographic fingerprint of C. deserticola by HPLC (Fig. 1) and used it to evaluate the difference of inherent qualities of samples from different habitats. Finally, notable differences were found in the quality of the samples from different habitats [82]. The same phenomenon was even observed during our research on the quality evaluation of C. deserticola, so later more serious concern should be paid to the quality consistency of Cistanche species.

Except planting, cultivation by cells or callus is another attractive alternative to solve the resource shortage of Herba Cistanche. During the cultivation process, many analytical methods have been established to analyze the cultivated result and to optimize the cultivated conditions [83–88]. The corresponding analytical conditions have also been summarized in Table 4.

As for the analysis of PhGs in complex products, Zhang reported a quantitation method of isoacteoside (12) in the total Cistanche glycosides capsules by HPLC [89]. We established a method for the analysis of acteoside (2) in Shenqiyinao capsules by HPLC [90], and Lei made a determination of echinacoside (11) in Congrong spirit by HPLC [91]. The key point of analyzing PhGs (phenylethanoid glycosides) in the complex products is to avoid the disturbance of other components, so, pretreatment of the sample and optimization of the chromatographic conditions are usually necessary.

3.1.2.3.2. Metabolic analysis of PhGs by HPLC.

In 2001, Lei first reported the metabolism process of PhGs (phenylethanoid glycosides) in the gastro intestine of beagle dogs, and four metabolites, echinacoside (11), acteoside (2), isoacteoside (12), and 2 -acetylacteoside (1) were isolated from feces by preparative HPLC [96]. In 2006, the metabolism of acteoside (2) and echinacoside (11), themain active constituents of Herba Cistanches were studied respectively, and their pharmacokinetics and bioavailabilities in rats were analyzed [97,98,134]. We established a sensitive LC-MS/MS method with a simple solid-phase extraction for the detection of acteoside (2) in rat plasma and tissue homogenates for the investigation of bioavailability and brain distribution in freely moving rats [97,134]. Jia developed a rapid and simple HPLC coupling with UV method to determine the content of echinacoside (11) in rat serum [98]. However, the bioavailabilities of echinacoside and acteoside were found to be only 0.83% and 0.12%, respectively, which was contradictory to the signifificant biological effects of PhGs (phenylethanoid glycosides) in animals [58–64]. In the future, further researches have to be made to elucidate the metabolic process and absorption mechanism of PhGs (phenylethanoid glycosides).

3.1.2.4. Analysis of PhGs (phenylethanoid glycosides) by high-speed counter-current chromatography (HSCCC).

HSCCC, a support-free liquid-liquid partition chromatography, eliminates irreversible adsorption of sample onto the stationary phase and has been widely used in preparative separation of natural products. Compared with the traditional solid-liquid column chromatography, it yields higher recovery and efficiency. Lei applied HSCCC to the separation and purifies- cation of acteoside (2) and 2-acetylacteoside (1) from C. salsa with a quaternary two-phase solvent system composed of ethyl acetate–n-butanol–ethanol-water (4:0.6:0.6:5, v/v). HPLC analysis of the CCC fractions revealed that the two PhGs (phenylethanoid glycosides) were over 98% purity [99]. Later, Li established a method using two solvent systems, one consisting of ethyl acetate–ethanol-water (5:0.5:4.5, v/v/v), and the other of ethyl acetate–n-butanol–ethanol-water (0.5:0.5:0.1:1, v/v/v/v) to isolate PhGs (phenylethanoid glycosides) from C. deserticola. Five PhGs (phenylethanoid glycosides), echinacoside (11), cistanoside A (3), acteoside (2), isoacteoside (12), and 2 -acetylacteoside (1) were isolated and purified, and the purities of these isolated compounds were all above 92.5% as determined by HPLC [100]. These methods supplied good references for the future isolation and purification of PhGs’ standards.

3.2. Benzyl glycosides

Recently, Lei reported the isolation and structure elucidation of three new benzyl glycosides, salsasides A–C (35–37, Fig. 2) from C. salsa, which was also benzyl glycosides isolated from Cistanche plants for the first time [47]. The structural features of these benzyl glycosides are similar to those of phenylethanoids isolated from this genus, except that the benzyl alcohol substituted phenethylol in the aglycone.

3.3. Iridoids

Up to now, three iridoid aglycones and fourteen iridoid glycosides have been isolated from Cistanche plants (38–54, Table 5) [102–109]. The structural features of iridoid glycosides from Cistanche plants are summarized as follows: glucose occurs in the C1 position of aglycone, with a confifiguration in H5 and H9; hydroxylation often occurs in C8 and C10 positions; sometimes, dehydration may happen between the hydroxyls of C10 with C1 or C3 to give an epoxy moiety.

3.4. Lignans

One lignan aglycones and fifive lignan glycosides have been isolated from C. deserticola and C. tubulosa plants (55–60, Table 6). The basic skeletons of these compounds are tetrahydrofuran and benzofuran lignans. The sources of that C. tubulosa from which several lignans have been isolated are mainly from Pakistan, while few lignans have been isolated from C. tubulosa collected in China. This further proved that the chemical differences existed between C. tubulosa from China and Pakistan [27,28].

3.5. Saccharides and their derivatives

3.5.1. Chemical study on saccharides and their derivatives

Carbohydrates comprise a high proportion of the dry mass of plants of Cistanche species [110]. Among them, one of the monosaccharides, galactitol has been reported as the main active component with laxative activity in Herba Cistanches [18,19,103,104]. While, the polysaccharides have been regarded as the active constituents with advancing body immunity, anti-aging, and anti-cancer activities in Herba Cistanches [20,21,111–113].

In the 90s, the studies on polysaccharides of Cistanche species had been focused on the isolation/purification and the analysis of the composition of monosaccharides [110,112,114–116]. The exact structures of polysaccharides from Cistanche species have not been clarifified until 1997. In Table 7, the elucidated structural properties of polysaccharides isolated from Cistanche species have been listed. Interestingly, all of these have been isolated from C. deserticola, and the polysaccharides in other Cistanche plants have not been studied.

Except these, some oligosaccharide derivatives, such as cistanoside F, cistanoside I, cistantubuloses A1/A2, and cistansinensose A1/A2 have also been isolated from Herba Cistanches (Fig. 3), which are actually the residues of PhGs (phenylethanoid glycosides) after losing the phenethylol aglycone. Since there are configurations existing in glucose in nature, sometimes, these oligosaccharide derivatives also exist as anomers, and this phenomenon could be observed from the paired NMR signals [37,39,40,11,45].

3.5.2. Analysis of saccharides and their derivatives

In order to evaluate the quality of Herba Cistanches comprehensively, galactitol, the main active component with laxative activity in Herba Cistanches [18,19,97,98] has been recently selected as an indicator to evaluate the quality of Herba Cistanches, combined with PhGs (phenylethanoid glycosides). In order to comprehensively evaluate the quality of C. tubulosa from different areas, Cai developed a method of quantitation of galactitol coupled with echinacoside (11) and acteoside (2) by HPLC. ELSD was selected as the detector for galactitol, due to its weak terminal absorption in the UV spectrum, and a Prevail Carbohydrate ES polymer gel column was used for its separation. Batches of C. deserticola and C. tubulosa from various habitats were measured, and the processing method of fresh C. tubulosa decoction pieces were also optimized by this method [92,93]. Their results showed that the contents of galactitol, echinacoside (11), and acteoside (2) in the C. tubulosa decoction piece by the described method were several times higher than those dried by insolation or by traditional method [93]. Additionally, Zhang ever established a TLC identification method of mannitol in C. deserticola, using ethyl acetate–pyridine–water (7:2:1) as developing solvent, and 1% KMnO4 solution as coloring agent [65].

As for the content determination of polysaccharides in Cistanche species, phenol–sulfuric acid is the most frequently used method, and the content of polysaccharides in C. salsa through different extraction methods was determined to be from 11.61% to 13.22% [123–125]. However, those are only some preliminary analytical results due to the limitation of the colorimetric method.

3.6. Alkaloids and their corresponding analysis

Up to now, only two alkaloids have been isolated from Cistanche species, that is betaine (65) and N, N-dimethyl glycine methyl ester (66) (Fig. 3) [126]. Betaine (65) is an alkaloid distributed commonly in plants, so there are more reports on its qualitative and quantitative analysis. Zhang compared the content variation of betaine in C. deserticola before and after processing, using a TLC identification combined with a colorimetric method [127]. This TLC method was also collected in Chinese Pharmacopoeia 2000 [8], while that quantitation method by colorimetry was later adopted by others to optimize the extraction technology of Herba Cistanches [128,129]. In 2007, Gong reported an HPLC method for the detection of betaine in Cistanche plants coupling with ELSD detector, and betaine had been found to exist only in C. deserticola, but not in C. tubulosa. Thus, the author suggested that betaine should be used as a marker to distinguish these two kinds of Cistanche plants [101]. However, considering that the sample batches are only two for each species, and one of the habitats of C. tubulosa (Yunnan) is uncertain, we recommended that this conclusion should be proven further. Additionally, the TLC identification of betaine for Herba Cistanche has been removed from Chinese Pharmacopoeia since 2005, due to its nonspecific property. Thus, taking it as a sole indicator to optimize the extraction technology of Herba Cistache was not reasonable [129].

3.7. Other compounds

There are small amounts of other compounds, such as phenolic glycosides, monoterpenoids, sterols or their glycosides, fatty acids, amino acids, and some trace elements, etc. existing in Cistanche plants [13,41,42,103,105,130–133].

4. Conclusions

In this review, the chemical constituents of Cistanche species and their analysis methods have been described. Among the existing analyses, the majority has been concentrated on PhGs (phenylethanoid glycosides), and HPLC has been the most widely used method due to its high efficiency and accuracy. Through analysis of the previous research works, combined with our years of study on Cistanche species, some major problems existing in the analysis of Cistanche plants have been summarized as follows: the first is the mixed usage of species source: C. deserticola and C. tubulosa are two official species collected in Chinese Pharmacopoeia. However, two other Cistanche species, C. salsa, and C. Sinensis are also used in some areas due to resource shortage. Although there have been several publications referring to the comparison between different species [6–8], they are not persuasive enough due to the limited sample batches and markers. Thus, it is necessary to establish a comprehensive method, such as fingerprinting technology to analyze comparatively the crude drugs of different sources. The second is that the quality inconsistency of Herba Cistanches has not been paid much attention to. Cistanche species are parasite herbs. There are many factors influencing their quality, such as climate, habitats, hosts, harvested time, processing method, and different parts of the same plant. Our studies showed that the quality of Cistanche species is not stable, especially that of the wild C. deserticola [80,82,92]. However, this problem had been neglected in some of the previous analyses, and only one or two samples had been used [74,76], which might lead to inaccurate conclusions. So, in the future, much more samples should be collected and analyzed to obtain a more objective conclusion. The third is that the present analyses mainly concentrate on two major PhGs (phenylethanoid glycosides), echinacoside (11) and acteoside (2), but as we know, the pharmacological action of TCM is the cooperation of multi-components or different types of constituents. Thus, simultaneous determination of the active multi-components is more meaningful for the quality control of TCM. However, up to now, there has been no quantitative analysis for more than three PhGs in Herba Cistanches, even there is no report on the analysis of benzyl glycosides, iridoids, and lignans. Then, future research should reinforce their analytical and pharmacological study. Overall, the present research on the analysis of Cistanche species is still in a lower-level state. Herba Cistanches are important tonic drugs, but actually, their quality could not be controlled effectively only by two representatives PhGs (phenylethanoid glycosides)[9]. The combination of multi-components determination with fingerprint has been regarded as a powerful approach for the quality control of TCMs. In the future, the research level of Cistanche species on these two fields should be further improved. Establishing a method, which could simultaneously qualitative and quantitative analysis of PhGs, iridoids, and other active constituents in Herba Cistanches will be a meaningful research direction.

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Acknowledgments

This work was financially supported by the National Natural science foundation of China (No. 30472070), and by the New-Century Talent Program, Ministry of Education of China (No. 985-2-102-113), and the authors are also grateful to Xiaoming Liu, Zhihong Song, LiLei from Peking University for their expert technical assistance.

From: ' Analysis of chemical constituents in Cistanche species' by Yong Jiang, Peng-Fei Tu

---Journal of Chromatography A, 1216 (2009) 1970–1979