TRITERPENOID AND STEROIDAL SAPONINS

Triterpenoids or triterpenoid saponins are pentacyclic molecules that are ultimately synthesized from isoprene. Steroidal saponins are tetracyclic molecules that are ultimately synthesized from acetyl coenzyme A (CoA).

Although they are structurally distinct, molecules of both types have most properties in common. The only other major differences between these two groups of constituents is that triterpenoids tend to be acidic in pH and occur more commonly in dicots than in monocots, and steroidal saponins tend to be neutral in pH and occur more commonly in monocots than in dicots.

Triterpenoids and steroidal saponins are inherently lipophilic. However, these molecules tend to occur as glycosides. Because of the large size of the saponin molecules, what results is that one end of the molecule (where the glycone is attached) is hydrophilic and the other end (the head of the aglycone) is hydrophobic. As a result of this, saponins act as emulsifying agents and detergents. When placed in water and shaken, they form foamy colloids and allow lipophilic and hydrophilic molecules to mix. Saponins can act as mild soaps by removing dirt particles, which gives them a soapy or acrid flavor. This property also seems to improve the absorption of certain botanical constituents (including other saponins) from the gut, when they are ingested simultaneously with saponins. The best published research on this effect confirms the traditional Chinese medical approach of frequently including saponin-rich plants in formulations, such as Panax ginseng (Asian ginseng) root.

Saponins can cause gastrointestinal distress through an unknown mechanism. Taking them with food tends to eliminate the problem. This same effect is theorized to be responsible for the reflex expectorant effect of saponins. When saponin-rich herbs, such as Hedera helix (ivy), are consumed orally, they tend to cause an increase in the production of mucus in the lungs, as well as coughing. This effect can be helpful for patients with coughs of all sorts, but particularly for those with dry cough. The reflex effect is believed to be neurologically mediated, but this has not been rigorously proved, and it is possible that saponins act directly within the lungs to provoke this effect.

Saponins, particularly those steroidal saponin-like molecules referred to as phytosterols, decrease cholesterol absorption from the gut, increase cholesterol excretion, and inhibit hepatic synthesis of cholesterol. All saponins tend to be immune modulating and have consistently shown antineoplastic effects. A wide range of other effects beyond these general properties of the group have been demonstrated with various specific saponins. A small sampling of this diversity can be seen with the saponins of Glycyrrhiza spp (licorice) root, particularly glycyrrhizin and its aglycone glycyrrhetinic acid. These molecules are anti-inflammatory and antiviral, inhibit cortisol catabolism, and have many other effects.

Saponin glycosides can cause hemolysis of red blood cells (Select Triterpenoid and Saponin-Rich Herbs). This primarily occurs when most saponins are injected intravenously or when they are hyperabsorbed from an abnormal gut. Some saponins have been successfully injected. Normally, saponins are not well absorbed orally, and the slow rate at which they are absorbed is more than sufficient to allow the body to adapt to them. This hemolytic effect does not appear to be related to the detergent properties of saponins but instead seems to be due to increasing cell membrane permeability. Overall, oral saponins appear to be extremely safe.