Ginsenosides orpanaxosides are a class ofnatural productsteroidglycosides andtriterpene saponins. Compounds in this family are found almost exclusively in the plant genusPanax (ginseng), which has a long history of use intraditional medicine that has led to the study ofpharmacological effects of ginseng compounds. As a class, ginsenosides exhibit a large variety of subtle and difficult-to-characterize biological effects when studied in isolation.[1]
Ginsenosides can be isolated from various parts of the plant, though typically from the roots, and can be purified by columnchromatography.[2] The chemical profiles ofPanax species are distinct; although Asian ginseng,Panax ginseng, has been most widely studied due to its use intraditional Chinese medicine, there are ginsenosides unique toAmerican ginseng (Panax quinquefolius) andJapanese ginseng (Panax japonicus). Ginsenoside content also varies significantly due to environmental effects.[3] The leaves and stems have emerged as a more abundant and easier-to-extract source of ginsenosides.[4] Ginsenosides have also been found injiaogulan, making jiaogulan the first plant outside ofAraliaceae to contain ginsenosides.[5]
Ginsenosides are named according to theirretention factor inthin layer chromatography (TLC). The letter or number after R is a serial indication of the retention factor, with '0' being most polar, followed by 'a' for the second-most polar, to 'h' being a fairly non-polar ginsenoside. Some of these groups turn out to consist of several molecules are further broken down with numbers: for example, Ra1 is more polar than Ra2. Terms such as "20-gluco-f" may be used to indicate further modification.[6]
A different nomenclature is applied to so-called pseudoginsenosides and notoginsenosides. The difference in name reflects more about the circumstances of their discovery than about their chemical nature.[7]
They can be broadly divided into two groups based on the carbon skeletons of theiraglycones: the four-ringdammarane family, which contains the majority of known ginsenosides, and theoleanane family. The dammaranes further subdivided into 2 main groups, theprotopanaxadiols (PPDs) andprotopanaxatriols (PPTs),[6] with other smaller groups such as the ocotillol-typepseudoginsenoside F11 and its derivatives.[3]
To each ginsenoside is bound at least 2 or 3hydroxyl groups at the carbon-3 and -20 positions or the carbon-3, -6, and -20 positions respectively. In protopanaxadiols, sugar groups attach to the 3-position of the carbon skeleton, while in comparison sugar groups attach to the carbon-6 position in protopanaxatriols. Well known protopanaxadiols include Rb1, Rb2, Rc, Rd, Rg3, Rh2, and Rh3. Well known protopanaxatriols include Re, Rg1, Rg2, and Rh1.[8]
Ginsenosides that are a member of theoleanane family are pentacyclic, composed of a five ring carbon skeleton.[9] R0 (also written Ro) is an example.[7]
Thebiosynthetic pathway of ginsenosides start in a way common to most steroids, fromsqualene to2,3-oxidosqualene via the action ofsqualene epoxidase, at which point dammaranes can be synthesized throughdammarenediol synthase and oleananes throughbeta-amyrin synthase.[6] As of 2021, the full conversion pathway to protopanaxadiol, protopanaxatriol, and oleanolic acid are known with each step having been assigned at least one gene. Ootillol synthesis remains unclear: 2,3-oxidosqualene is believed to first be converted into 2,3,22,23-dioxidosqualene. An unknownoxidosqualene cyclase produces 3-epicabraleadiol, which is the immediate precursor to ootillol.[7]
In the proposed pathway, squalene is synthesized from the assembly of twofarnesyl diphosphate (FPP) molecules. Each molecule of FPP is in turn the product of two molecules ofdimethylallyl diphosphate and two molecules of isopentenyl diphosphate (IPP). IPP is produced by themevalonic pathway in thecytosol of a ginseng plant cell and by themethylerythritol phosphate pathway in the plant'splastid.[10]
ManyUGT enzymes found in the genome of variousPanax species are known to be responsible for attaching sugars onto the sterol skeleton, producing ginsenosides. A handful of reactions still don't have an identified UGT. Enzymes responsible for attaching other side chains such as acidic groups and acyls are not yet identified.[7]
Ginsenosides likely serve as mechanisms forplant defense.[10] Exposingin vitro cultures of ginseng cells to the plant defense signalmethyl jasmonate causes increased production of ginsenosides.[11] Ginsenosides have been found to have bothantimicrobial and antifungal properties. Ginsenoside molecules are naturally bitter-tasting and discourage insects and other animals from consuming the plant.[10] It's also been proposed that ginsenosides may interfere with insect growth by mimickingecdysteroids,[11] though inDrosophilia fruit flies this mimicking activity actually increases fertility.[12]
Steaming ginseng causes ginsenosides to lose their sugar and malonyl side chains, converting more polar molecules into the rarer (in nature), less-polar ones. This change may be responsible for the different effects attributed to red ginseng vs. white ginseng. The same is true of the pulp of the ginseng fruit.[13] Similarly, heat and acid treatment of the stem and leaves can produce less-polar ginsenosides. In general, the less-polar molecules are believed to be easier to be absorbed and to bind onto cell membranes. Some reports claim a stronger biological activityin vitro.[14]
Ginseng is generally consumed orally as adietary supplement, and thus its component ginsenosides may be metabolized bygut flora to less-polar molecules. For example, ginsenosidesRb1 and Rb2 are converted to 20-b-O-glucopyranosyl-20(S)-protopanaxadiol or 20(S)-protopanaxadiol by human gut bacteria.[15] This process is known to vary significantly between individuals.[16] In some cases themetabolites of ginsenosides may be the biologically active compounds.[11]
Most studies of the biological effects of ginsenosides have been incell culture oranimal models and thus their relevance to human biology is unknown. Effects on thecardiovascular system,central nervous system andimmune system have been reported, primarily inrodents.Antiproliferative effects have also been described.[1][11]
Many studies suggest that ginsenosides have antioxidant properties. Ginsenosides have been observed to increase internal antioxidant enzymes and act as a free-radical scavenger.[8] Ginsenosides Rg3 and Rh2 have been observed in cell models as having an inhibitory effect on the cell growth of various cancer cells while studies in animal models have suggested that ginsenosides haveneuroprotective properties and could be useful in treatingneurodegenerative disease such asAlzheimer's andParkinson's diseases.[8]
Two broadmechanisms of action have been suggested for ginsenoside activity, based on their similarity tosteroid hormones. They areamphiphilic and may interact with and change the properties ofcell membranes.[1] Some ginsenosides have also been shown to bepartial agonists ofsteroid hormone receptors. It is not known how these mechanisms yield the reported biological effects of ginsenosides. The molecules as a class have lowbioavailability due to both metabolism and poor intestinal absorption.[11]
Although traditionally sourced from the root following folk medicine use, ginsenosides have been isolated from other parts of the plant. The concentration in the stems and leaves of Asian ginseng is 3-6%, compared to just 1-3% in the root.[14] Compared to the root, ginseng fruit pulp contains 7 times the amount of ginsenoside Re and 4 times the amount of total ginsenosides.[13]
Cell and tissue culture has also produced significant amounts of ginsenoside, especially when key biosynthetic genes areoverexpressed.[7]
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