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Ginsenosides or panaxosides are a class of natural product steroid and triterpene saponins. Compounds in this family are found almost exclusively in the plant genus Panax (ginseng), which has a long history of use in traditional medicine that has led to the study of pharmacological effects of ginseng compounds. As a class, ginsenosides exhibit a large variety of subtle and difficult-to-characterize biological effects when studied in isolation.
Ginsenosides can be isolated from various parts of the plant, though typically from the roots, and can be purified by column chromatography. The chemical profiles of Panax species are distinct; although Asian ginseng, Panax ginseng, has been most widely studied due to its use in traditional Chinese medicine, there are ginsenosides unique to American ginseng ( Panax quinquefolius) and Japanese ginseng ( Panax japonicus). Ginsenoside content also varies significantly due to environmental effects. The leaves and stems have emerged as a more abundant and easier-to-extract source of ginsenosides. Ginsenosides have also been found in jiaogulan, making jiaogulan the first plant outside of Araliaceae to contain ginsenosides.
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.
To each ginsenoside is bound at least 2 or 3 hydroxyl 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.
Ginsenosides that are a member of the oleanane family are pentacyclic, composed of a five ring carbon skeleton. R0 (also written Ro) is an example.
In the proposed pathway, squalene is synthesized from the assembly of two farnesyl diphosphate (FPP) molecules. Each molecule of FPP is in turn the product of two molecules of dimethylallyl diphosphate and two molecules of isopentenyl diphosphate (IPP). IPP is produced by the mevalonic pathway in the cytosol of a ginseng plant cell and by the methylerythritol phosphate pathway in the plant's plastid.
Many UGT enzymes found in the genome of various Panax 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.
Ginsenosides likely serve as mechanisms for plant defense. Exposing in vitro cultures of ginseng cells to the plant defense signal methyl jasmonate causes increased production of ginsenosides. Ginsenosides have been found to have both antimicrobial and antifungal properties. Ginsenoside molecules are naturally bitter-tasting and discourage insects and other animals from consuming the plant. It's also been proposed that ginsenosides may interfere with insect growth by mimicking , though in Drosophilia fruit flies this mimicking activity actually increases fertility.
Many studies suggest that ginsenosides have antioxidant properties. Ginsenosides have been observed to increase internal antioxidant enzymes and act as a free-radical scavenger. 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 have Neuroprotection properties and could be useful in treating neurodegenerative disease such as Alzheimer's and Parkinson's diseases.
Two broad mechanisms of action have been suggested for ginsenoside activity, based on their similarity to . They are amphiphilic and may interact with and change the properties of . Some ginsenosides have also been shown to be of steroid hormone receptors. It is not known how these mechanisms yield the reported biological effects of ginsenosides. The molecules as a class have low bioavailability due to both metabolism and poor intestinal absorption.
Cell and tissue culture has also produced significant amounts of ginsenoside, especially when key biosynthetic genes are overexpressed.
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