Silymarin (SIL) is an extract of Milk thistle (Silybum marianum), which has been used for 2000 years. Milk thistle has been used since the 16th century for liver disease and SIL has been marketed since 1969.
SIL is a standard extract of the Milk thistle fruit and seed and standardized Milk thistle is 70% SIL. Silymarin is made of flavonoids bonded to lignans and there are four flavonolignans in SIL which are:
Silibinin (SB), the main active ingredient.
Since SIL is not well absorbed, SB is frequently combined with phosphatidyl-choline to improve absorption.
SIL is especially used for hepatobiliary disease or poor flow of bile. This would include hepatitis, cirrhosis, jaundice, chronic liver disease and gallstones. SIL can also work in drug-induced liver disease. The mechanism of action is unknown in these diseases.
In alcoholic liver cirrhosis, SIL improves liver function testing and reduces mortality. The results in acute and chronic hepatitis are variable. The studies of liver disease from chemical and drug damage are old and the authors feel that the results are inadequate for conclusions.
Studies of SIL show no adverse reactions and no interactions with drugs. No perinatal (five months before to one month after birth) toxicity is seen in mothers or babies and no toxicity is seen when SIL is used during lactation. SIL has the following effects:
1. RNA stimulation induces protein production.
2. Antioxidant effects prevent the oxidation of fats.
3. Stabilization of cell membranes to protect cells.
4. Prevents tissue scarring by inhibiting 5-lipoxygenase, the enzyme which converts arachidonic acid to leucotrienes. This reduces stellate and fibroblast cell formation.
5. Reduces the effects of poisoning with Amanita phalloides.
Bile flow is improved by SIL, which is choleretic and anticholestatic. Cholestasis is impaired bile flow. The formation of bile occurs by osmosis across cell walls from liver cells into tiny bile canals, which join until they form large bile ducts.
The transport of bile across membranes depends on proteins called transport proteins. RNA damage can reduce the synthesis of these proteins. Drugs that cause the side effect of cholestasis can reduce the protein production and changes in cell wall rigidity can reduce the flow of bile across cell membranes.
The increase of estrogen in the third trimester of pregnancy causes cholestasis in some women. Cholestasis can also result from oral contraceptives and post-menopausal estrogen replacement. SIL can prevent the cholestasis caused by estrogens and is especially useful for increasing bile production in pregnancy-related cholestasis since it has low toxicity. SIL increases bile salt production by increasing bicarbonate production.
CONCLUSION: Milk thistle extracts are beneficial in a number of liver diseases without side effects. The method of action is not known, but the extract of Milk thistle, SIL, has been shown to increase the production of proteins that transport bile salts out of liver cells into bile ducts.
NOTE: Cholestasis refers to a stop in the flow of bile. It can come from a problem of the liver or of its drainage system. A choleretic agent increases the flow of bile.
5-lipoxygenase inhibition has been shown to block some forms of cancer.