Ginsenoside Re: Its chemistry, metabolism and pharmacokinetics
© Peng et al; licensee BioMed Central Ltd. 2012
Received: 21 July 2011
Accepted: 7 February 2012
Published: 7 February 2012
Ginsenosides, the bioactive components of ginseng, can be divided into two major groups, namely 20(S)-protopanaxatriol (e.g. Re, Rg1, Rg2, and Rb3) and 20(S)-protopanaxadiol (e.g. Rb1, Rb2, Rc, and Rd). Biological and environmental factors may affect the content of ginsenosides in different parts of ginseng plant. Evidence from pharmacokinetic and metabolic studies of Re demonstrated that (1) the absorption of Re is fast in gastrointestinal tract; (2) Re may be metabolized mainly to Rh1 and F1 by intestinal microflora before absorption into blood; and (3) Re is quickly cleared from the body.
Ginseng is a key herb in Chinese medicine, and has a wide range of therapeutic and pharmacological uses [1–3]. Panax ginseng is a slow growing perennial herb of the Araliaceae family usually cultivated in China, Japan, Korea and Russia, as well as in the United States and Canada. Ginseng root has been used as an oriental folk medicine for several thousand years [2, 4]. It is a highly valued medicinal plant in the Far East that and also popular in the West in the past 20 years [2, 4–7].
A number of studies suggest that both Panax ginseng C.A. Meyer (also known as Asian ginseng, Chinese ginseng or Korea ginseng) and Panax quinquefolius (also known as American ginseng) have multiple components and pharmacological functions [7–14]. Among the complex constituents of ginseng, ginsenosides (also known as ginseng saponins or triterpene saponins) are the major components responsible for biochemical and pharmacological actions of ginseng [9, 15–17]. With the development of modern technology, more than 150 naturally occurring ginsenosides have been isolated from Panax species . About 40 ginsenosides have been identified from the root of Panax ginseng [1, 19–22].
Chemistry and content
Chemical structure of Re
Rg1, Rc, Rd, Re, Rb1, Rb2 and Rb0 are the main ginsenosides in quantity [1, 33]. The top six major ginsenosides (Rb1, Re, Rd, Rc, Rg1 and Rb3) make up over 70% of total ginsenoside content in P. quinquefolius [34, 35].
Content of Re in ginseng
The biological and environmental factors that may affect the quantity and quality of ginsenosides in ginseng [14, 35] include the species, age, part of the plant, season of harvest, method of cultivation, and means of preservation. For example, the content of Re, Rg1 and Rd is higher in the wild P. ginseng roots than in the cultivated ginseng roots, while the content of Rc, Rb2 and Rb1 is lower in the wild P. ginseng roots than in the cultivated ones. These differences in content of ginsenosides might affect their biological and pharmacological properties. Root ginsenoside content depends on the age of ginseng plant. For example, the plants younger than four years of age are considered unsuitable for harvest due to their low ginsenoside content [35, 42–44]. Lim et al.  determined the genotypes and environmental factors affecting the ginsenoside content among eight wild populations of P. quinquefolius. The influence of genotypes and environment on ginsenoside content varies among different types of ginsenosides. Specifically, the Re content varies with populations but not locations, whereas Rb1, Rc and Rb2 only varies with locations, and Rg1 and Rd varies with both. Ginsenoside levels are decreased, while ginseng growth is increased, at an intensively managed garden location. The content and composition of ginsenosides vary with other environmental conditions such as the type of soil, temperature, light intensity and water content .
Using high pressure microwave-assisted extraction (HPMAE) and high-performance liquid chromatography (HPLC) coupled with evaporative light scattering detection (ELSD), i.e. HPMAE HPLC-ELSD, Qu et al.  studied the effects of different parts and age of P. quinquefolius on the content of 12 ginsenosides, namely Rg1, Re, Rf, Rg2, Rh1, Rb1, Rc, Rb2, Rb3, Rd, Rh2 and F11. The study ranked the parts of five-years-old P. quinquefolius in terms of total content of these 12 ginsenosides in a descending order: leaf, root-hair, rhizome, main root and stem, suggesting that the leaf could be a better source for ginsenosides, as compared with other parts of ginseng plant. It also found that in ginseng roots, the content of Re and Rb1, the major ginsenosides, increase with age of the plant.
In a comparative study on the quality of Tongrentang Red Ginseng and Korean Red Ginseng, Wu et al  found that the content of Re, Rg1 and Rb1 in the Tongrentang Red Ginseng is less than the content in the Korean Red Ginseng.
Another extensive study  performed a quantitative analysis of Re, Rb1 and Rg1 in P. quinquefolius berry and flower sampled in various months throughout the year, by enzyme-linked immunosorbent assay (ELISA). The P. quinquefolius flower had higher content of Re, Rb1 and Rg1 and the lowest content of Re in the berries harvested in September . To analyze the Re content in P. quinquefolius berry pulp extracts, Morinaga et al.  performed a new Eastern blot technique with anti-Re monoclonal antibody, and confirmed that the content of Re varies from part to part in the plant.
Lee et al.  reported the variations in the ginsenoside profiles of ginseng landraces in Korea. They found that the P. ginseng wild population exhibits three types of ginsenoside profiles affected by genetic and environmental factors.
Metabolism and pharmacokinetics
After oral administration, Re is in contact with the gastriointestinal fluids containing gastric acids and gastric enzymes, intestinal enzymes, and colonic bacteria [51, 52]. Li et al. [23, 53] studied the pharmacokinetic parameters and absolute bioavailability of Re, R1, Rg1, Rd, and Rb1 after oral or intravenous administration of total notoginsenosides. Main pharmacokinetic parameters of these constituents were determined by Drug and Statistics (DAS) for Windows pharmacokinetics software. The results showed that Re, R1, Rg1, Rd and Rb1 reached peak concentration in plasma within about 45 minutes after oral administration of total panax notoginsenoside (TPNG) powder in rats, suggesting a rapid absorption of ginsenosides in gastrointestinal tract. The absolute bioavailability of Re was 7.06% . To confirm the rapid absorption finding, Joo et al.  conducted a pharmacokinetic study using ICR mice and ultra performance liquid chromatography-electrospray ionization-mass spectrometry (UPLC-ESI-MS) analytical method. This pharmacokinetic study  revealed that the time to reach the peak plasma concentration after oral administration was 0.4 ± 0.2 hour. The data also showed that the oral bioavailability was 0.19-0.28%. Qi et al.  found that the oral bioavailability of PPD ginsenosides (Ra3, Rb1, Rd, Rg3 and Rh2) and PPT ginsenosides (Rg1, Re, Rh1, and R1) was less than 5% and PPT ginsenosides had better bioavailability, possibly due to the faster degradation of PPD ginsenosides.
Metabolism and biotransformation
Metabolic research of Re in animals was also reported . Six SD rats were used and divided into three groups. Feces were collected at 12, 24, 36, 48 and 60 hours after oral administration of Re (100mg/kg). Six metabolites of Re were detected in the feces of rat. The structures of the metabolites were identified as 20(S)-ginsenoside Rg2, 20(S)-ginsenoside Rh1, 20(R)-ginsenoside Rh1, ginsenoside F1, 3-oxo-ginsenoside Rh1 and PPT. The metabolic pathways of Re in animals were similar to those in humans .
A similar metabolic study was also carried out in vivo with HPLC coupled with electrospray ionization and quadrupole time-of-flight tandem mass spectrometry (HPLC-ESI-TOF-MS/MS) . The rat urine samples were collected and pretreated through C(18) solid-phase extraction cartridges prior to analysis. As a result, eleven and nine metabolites together with Re were detected and identified in rat urine after oral and intravenous administration, respectively. Oxidation and deglycosylation were found to be the major metabolic processes of the constituent in rat, indicating that a large part of the intact ginsenosides was metabolized and transformed to ginsenosides with more biological effects in the gastrointestinal tract . PPT ginsenosides, such as Re and Rg1, were mainly converted to Rh1 and F1 and then to corresponding aglycones [51, 56].
Xia et al.  applied a developed and validated liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) method to detect Re, Rg1, Rd, Rb1 and ophiopogonin D in rat plasma. Re and Rg1 were eliminated quickly from the body. The pharmacokinetic behaviors of Rd and Rb1 were significantly different from those of Re and Rg1 in rat. Joo et al.  found that Re was rapidly cleared from the body within 0.2 ± 0.03 hour for male mice and 0.5 ± 0.08 hour for female mice after intravenous administration. They also found that ginseng berry extract exhibited a superior oral absorption of Re as compared to orally fed Re, suggesting that ginseng berry extract may be of choice for Re intake .
The plasma concentrations of Re and Rg1 were determined and the pharmacokinetic parameters were calculated after intravenous Shenmai injection in ten volunteers . The study found the distribution and elimination of Re and Rg1 to be rapid after intravenous injection; and the pharmacokinetic characteristics could be fitted to the two-compartment model of pharmacokinetics.
Multiple biological and environmental factors affect the quantity and quality of ginsenosides in ginseng parts. Studies on Re demonstrate that (1) the absorption of Re is quick in rats; (2) PPT, Re and Rg1, are likely to be metabolized to Rh1 and F1 by intestinal microflora before absorption into the blood; and (3) Re can be quickly eliminated from the body.
Drug and Statistics for Windows pharmacokinetic software
enzyme-linked immunosorbent assay
ginsenoside Re (Rg1, Rg2, Rg3, Rf, Rb1, Rb2, Rb3, Rc, Rd, and Re1 - Re6 are the same abbreviations with Re)
high-performance liquid chromatography coupled with electrospray ionization and quadrupole time-of-flight tandem mass spectrometry
high-performance liquid chromatography coupled with evaporative light scattering detection
high pressure microwave-assisted extraction
liquid chromatography-electrospray ionization-mass spectrometry
total Panax notoginsenoside
ultra performance liquid chromatography mass spectrometry
The work of LHX is supported by NIH/NHLBI R01 HL97979.
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