CHEMTECH
April 1998
CHEMTECH 1998, 28(4), 26-32.
Copyright © 1998 by the American Chemical Society.


Getting to the root of ginseng

This popular phytomedicine is being touted for a wide variety of uses. Examination of its biochemical, pharmaceutical, and medical perspectives sheds light on how it works and why.

Otto Sticher


Ginseng, the root of Panax ginseng of the Araliaceae family, has been used in Oriental medicine since ancient times as a stimulant, tonic, diuretic, and digestive aid. In Europe, ginseng phytomedicines are sold over-the-counter and taken to increase physical and mental performance, to provide resistance to stress and disease, and to prevent exhaustion. In 1994, retail sales there were approximately $50 million. Almost half (49%) of the European market is in Germany, followed by Spain (14%), France (13%), and Switzerland (11%) (1).

In this article, I provide an update on the chemistry, biological effects, molecular mechanisms, possible therapeutic uses, and quality control of P. ginseng and of phytomedicines based on root extracts of this plant. I emphasize the ginsenoside structures that are considered to be the main active compounds and their quantitative determination in ginseng roots and phytomedicines.

The plant
During the Han dynasty (from 206 B.C. to 24 A.D.), a medical text was written about a plant called sheng. Later, the plant became known as "Jen Sheng, the root of heaven" or "ginseng", which literally means "man-herb", because its root is shaped like a human body. In 1883, the genus Panax was added to the name (pan meaning "all" and axos meaning "cure"). Thus the meaning of Panax ginseng is "the all-healing man-herb", and it is indeed regarded as something of a panacea, particularly in the Far East (2).

Several Panax species grow in the Northern Hemisphere, from the eastern Himalaya through China and Japan to North America (see sidebar, Other Panax species). Originally, P. ginseng C. A. Meyer (Korean ginseng) grew in northeastern China, Korea, and far-eastern Siberia, but now the wild plant is very rare. Today, almost all the ginseng roots on the market are cultivated in China, Korea, and Japan.


TO SIDEBAR: Other Panax species


Ginseng is a perennial aromatic herb with a short underground stem (rhizome) associated with a fleshy white root (Figure 1). Its root system consists of the primary root and its branches and of some adventitious roots developed from the rhizome (6). The aboveground part of that plant is a single stem about 30-60 cm high (in cultivation, 60-70 cm) that dies annually. At the age of three or four years, the plant begins to flower, in June or July. A flowering plant may bear three to six palmately compound leaves, each with five leaflets, and a peduncle terminated by a simple umbel at the center with 4-40 flowers, depending on the age of the plant and its growing conditions. The fruit is the size of a pea, green at first and red at maturity, and contains two or three white seeds.


figure 1 Figure 1. The ginseng plant.

Because of continual harvest and use over thousands of years, the natural supply of ginseng root was exhausted long ago. Where ginseng grows naturally, it is in the cool temperate zone in rich, damp--but not wet or muddy--soil; it prefers the shade of hardwood forests.

The cultivation of ginseng requires good drainage, artificial shade, and much patience from the initial planting to root harvest. Ginseng is propagated in the spring from seeds that are harvested from ripe fruits of 4- to 5-year-old plants collected the previous season. In a nursery bed, 25-30 seeds are sown in horizontal furrows 4-6 cm apart and then covered with about 3 cm of soil. The seeds germinate in 18-20 months, and the seedlings may be transplanted to permanent beds when they are one or two years old. Four to six years later, the root is harvested.

Wind, rain, and direct sun can be harmful to ginseng plants. Therefore, frames for artificial shelter must be built over the beds, and the ground must be kept moist. Because ginseng is a root crop, preventing the plants from flowering (by picking the flower buds off as they form) produces larger and better roots.

Ginseng is harvested between August and October, when the aboveground portion turns yellow. Careful handling of the roots is very important. The branching main roots are 8-20 cm long and about 2 cm thick; the thin ends of the main and secondary roots are traditionally removed, making the human form more evident (6).

Ginseng products are one of two kinds: white or red. The kind of product is determined by the process used to prepare it. White ginseng is the dried root, the skin of which is normally peeled off. Red ginseng is the steamed root, caramel-colored and resistant to the invasion of fungi and worms (3). In the European phytomedicines market, white ginseng (including lateral roots and root hairs) is commonly used as crude material, whereas red ginseng is preferred in Asian traditional medicine.

Constituents
The constituents of ginseng root have been investigated since the beginning of the 20th century, and several classes of compounds have been isolated: triterpene saponins; essential oil-containing polyacetylenes and sesquiterpenes; polysaccharides; peptidoglycans; nitrogen-containing compounds; and various ubiquitous compounds such as fatty acids, carbohydrates, and phenolic compounds (7).

The chemical constituents of ginseng that are believed to contribute to its pharmacological effects have been investigated extensively since 1955. These compounds are triterpene saponins, named ginsenosides Rx according to their mobility on thin-layer chromatography plates, with polarity decreasing from index "a" to "h" (Figure 2). This property is a function of the number of monosaccharide residues in the sugar chain (8).


figure 2 Figure 2. Thin-layer chromatograms...

Acid hydrolysis of the genuine glycosides originally yielded two aglycones, panaxadiol and panaxatriol, now known to be artifacts produced by the action of acid during the process of hydrolysis (3). By applying various chemical and spectroscopic methods, researchers have found that the genuine aglycones were protopanaxadiol and protopanaxatriol, which both have a dammarane skeleton (3, 4). On acid treatment of protopanaxadiol and protopanaxatriol, a tertiary hydroxyl group attached to C-20 participates in ring closure with a double bond in the side chain (Figure 3).


figure 3 Figure 3. The ginseng saponins...

So far, 31 ginsenosides have been isolated from the roots of white and red ginseng (3, 4, 9-15). They can be categorized in three groups depending on their aglycones: protopanaxadiol-type ginsenosides, protopanaxatriol-type ginsenosides, and oleanolic acid-type saponins.

All dammarane ginsenosides isolated from ginseng root (white ginseng) are derivatives of the 20S protopanaxadiol (Table 1) and the 20S protopanaxatriol (Table 2), with the exceptions of 20R ginsenoside Rg3 (9, 16), Rh4 (15), and koryoginsenoside R2 (12). Almost all the ginsenosides isolated from white ginseng are also found in red ginseng; however, some ginsenosides--the 20R Rg2; the 20R Rh1; and Rh2, Rs1, Rs2, Q-R1, and NG-R1--are characteristic saponins for red ginseng. The 20R compounds are degradation products formed by heating and hydrolysis during the steaming process (3, 7). Therefore, the natural occurrence of either 20R or 20S Rg3 needs to be verified. From recently published high-performance liquid chromatography (HPLC) investigations, it is unclear whether both compounds occur in both white and red ginseng (13) or only in red ginseng (14).


Table 1 Table 1. The saponins of protopanaxadiol

Table 2 Table 2. The saponins of protopanaxatriol

Pharmacological effects
Overviews of the pharmacological effects of ginseng extracts and preparations; ginsenoside, polyacetylene, and polysaccharide fractions; and single ginsenosides and polyacetylenes have been presented by several authors (3-4, 7, 17-20). Ginseng is specified in the German, Swiss, Austrian, and French pharmacopeias, among others. The Swiss pharmacopeia demands a total ginsenoside content, calculated as ginsenoside Rg1, of not less than 2.0%. According to the German pharmacopeia, the total ginsenoside content should be not less than 1.5%. Both pharmacopeias use a spectrophotometric method for quantification. However, a draft for the European pharmacopeia demands the content of ginsenosides Rg1 and Rb1 to be not less than 0.3%, measured with an HPLC method.

The main activities for ginseng noted in the older literature (7), in addition to use as a general tonic, were

  • stimulation of immunological function;
  • effects on the cardiovascular system, for example, lowering blood pressure;
  • effects on lipid metabolism shown by decreases in serum levels of total cholesterol, low-density lipoprotein cholesterol and triglycerides and increases of serum level high-density lipoprotein cholesterol;
  • effect on alcohol metabolism shown by the stimulation of alcohol dehydrogenase and the oxidation of alcohol in the liver;
  • lowering of blood sugar levels;
  • stimulation of the pituitary-adrenocortical system; and
  • inhibition of tumor growth.

It has been claimed that Rg1 stimulates the central nervous system and enhances protein, DNA, and RNA synthesis, whereas Rb1 has tranquilizing effects on the central nervous system and improves memory (7, and references therein).

More recently published sources cite the kinds of activity listed in Table 3. Many of these effects can be broadly characterized under the heading of antiaging. Ginseng has been reported to have an inhibitory effect on the proliferation of cancer cells. It has also been reported to have a positive effect on the immune system, stimulating the phagocytic function of the reticoloendothelial system leading to an increase in serum-specific antibodies and IgG content and also an increase in the relative percentages of protective B-lymphocytes. Therefore it is not surprising that ginseng is used by Asians to promote longevity.

Table 3 Table 3. Effects claimed for ginseng.

Ginseng is used primarily as a general tonic or geriatric remedy to regulate the catabolic and anabolic processes of cellular metabolism, to increase the capacity of the organism to adapt to mental and physical stress, and to increase concentration and attention.

In general, the experimentally shown effects have been observed in their totality only with the use of the whole extract; no single constituents have been used individually. Only recently has the role of compounds other than the ginsenosides been demonstrated for the ginseng extract. The isolated polyacetylenes (22, 23, 26-29, 41)--mainly panaxytriol, panaxynol, and panaxydol (Figure 4)--show cytotoxic, antiplatelet, and anti-inflammatory effects, respectively.


figure 4 Figure 4. Polyactylenes...

The polysaccharides--particularly the panaxans A-U (42-47), which are peptidoglycans--are responsible for ginseng's hypoglycemic activity. The ginsenans PA, PB, S-IA, and S-IIA and some other polysaccharides (35-37) show immunological activity such as recticuloendothelial system (RES) potentiation, effects on the body's unspecific immune system, and alkaline phosphatase-inducing activity (31, 48, and references therein). Various polysaccharides show cytoprotective activity and antitumor activity. The structures of the isolated polysaccharides are only partially known. The backbone chain of ginsenan PA, for example, consists mainly of ß-1,3-linked D-galactose (35).

Pharmacokinetics and metabolism of ginsenosides
Until recently, little was known about the absorption, distribution, excretion, and metabolism of ginseng saponins. In the past decade, various investigations dealing with the pharmacokinetics and metabolism of ginsenosides have been published. From these studies, it can be concluded that the decomposition modes are different for protopanaxadiol and protopanaxatriol saponins.

Ginsenoside Rg1 (protopanaxatriol-type) showed an extremely short half-life of 27 min after intravenous administration into minipigs. In contrast, the protopanaxadiol-type ginsenoside Rb1 showed a half-life in the ß-phase of 16 h. These results correlated with the pharmacokinetic results in rats and in rabbits. The high persistence of Rb1 in serum and tissues was attributed to a high degree of plasma protein binding (7, 49-51).

Rg1 was rapidly absorbed by mice after oral administration (~30% after 1 h). The concentration of Rg1 and metabolites was high in the blood, liver, bile, subcutis, conjunctiva, and epithelia of the oral cavity, esophagus, and nasal cavity; the concentration was low in muscle and endocrine organs and very low in the brain. Rg1 also was metabolized rapidly. Intact Rg1 was excreted in mouse urine and feces in very small amounts, but the metabolite concentration was high. Five metabolites could be detected; two of them were ginsenoside Rh1 and 25-OH-Rh1 (7, 52-53).

Intact cells were used to study the metabolism of ginsenoside Rh2. In a medium containing 2% fetal calf serum and B16 melanoma cells, uptake reached a maximum after 3-6 h (54). Rh2 was deglycosylated to protopanaxadiol. Ginsenoside Rh2 and protopanaxadiol inhibited the growth of B16 melanoma cells.

Assuring quality
In the past two decades, many attempts have been made to identify and quantify the ginsenosides in crude plant material and in commercial preparations. For identification, techniques ranging from TLC (55, 56) to randomly amplified polymorphic DNA fingerprinting (57, 58) have been used. For the quantification (and identification) of ginsenosides, methods have ranged from colorimetry (59-61) to droplet counter-current chromatography spectrophotometry (62).

The favored method of identification and quantification of ginsenosides, at least in quality control, is HPLC using reversed phase-octadecylsilane (RP-ODS) columns followed by UV detection. In certain cases, especially for the rapid identification of ginsenosides in plant material or for their determination in biological fluids, methods such as liquid chromatography/mass spectrometry or radioimmunoassay are used.

Sample cleanup has long been a limiting factor for ginseng analysis by HPLC. Solvent extraction and solid-phase extraction methods have been used. Now, sample cleanup using SepPak cartridges from Waters (Milford, MA) seems to be the most suitable extract purification procedure. In principle, all the columns used for solid-phase extraction are used for the same purpose and are based on the selective elution of the compounds of interest. Interfering compounds are washed through the columns or remain on the cartridge.

Most of the HPLC approaches used today in quality control go back to a method developed in our laboratory in the 1970s (63). We used RP-ODS columns and acetonitrile-water mixtures as mobile phase. Using acetonitrile and water (30/70), six of the ginsenosides--Rd, Rb2, Rc, Rb1, Rg2, and Rf (but not Rg1 or Re)--could be separated and quantitatively determined. The separation of Rg1 and Re was possible using the same solvent in an 18/82 ratio. Later, at a ginseng meeting in Hong Kong, we presented an improved HPLC method (also developed in our laboratory) that uses a programmed elution technique and a photodiode array detection system (64). This programmed elution technique made it possible to separate all eight ginsenosides in one analytical run.

HPLC separations such as the one published by Samukawa and co-authors (14) enable the separation of additional ginsenosides; 22 ginsenosides can be separated in a single run (Figure 5). Such methods are useful for the differentiation of white and red ginseng, for example, and for the detection of degradation products. However, they are not useful for a quantitative determination. As shown in the chromatograms in Figure 5, malonyl ginsenosides occur only in white ginseng, whereas red ginseng shows additional peaks for Rh1, 20R Rh1, 20R Rg2, Q-R1, Rs1, and 20S and 20R Rg3.


figure 5 Figure 5. An HPLC gradient...

Conclusions
The chemical constituents of P. ginseng are known, and available analytical methods satisfy the highest standards in the quality control of ginseng preparations. However, many studies are under way to investigate the pharmacological effects of the total extract and of single plant constituents as well as the medical use of ginseng preparations.

The metabolism of the chemical constituents of P. ginseng also has been investigated. Although much scientific work has been done in the field, there are unanswered questions about the active compounds, the relevance of the experimentally proven effects, and the therapeutic use of ginseng preparations. It is still unclear whether root extracts of P. ginseng can be replaced with leaf extracts or, possibly, extracts from other ginseng species that contain similar active compounds. Because ginseng preparations are used primarily as general tonics and geriatric remedies, it is difficult to describe the desired effects in scientific, measurable terms and to present quantitative results.


Acknowledgement
The author thanks Annemarie Suter for editorial assistance.


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REFERENCES
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