Silymarin

The Uses of Silymarin

Silymarin a flavonolignan complex extracted from milk thistle, has been shown to provide cytoprotective, antioxidant and hepatoprotective effects. Provides extracts such as (+)-taxifolin as an inhibitor of β-amyloid aggregation.

The Uses of Silymarin

Silymarin has been used to study:

• its in vitro antiviral, antibacterial, antifungal activities and cytotoxicity
• its effect of silymarin on bladder contractions in cyclophosphamide (CYP)-induced cystitis rat model
• its effect on liver toxication induced by Fumonisin B1 in mice

Indications

Milk thistle (Silybum [Carduus] marianus) is a spiny European plant with white-veined leaves and milky sap, the seed of which is used to treat liver disease.Milk thistle seed extract is used orally in the treatment of alcoholic and other cirrhoses and in Europe intravenously for its hepatoprotective effect in Amanita and other mushroom poisonings. It is grown in this country primarily as a “liver cleanser” and is reputed to protect this organ from a wide array of toxins.Milk thistle seed contains the active principle silymarin, a complex of flavonolignan compounds including silibinin (silybin), silidianin, and silychristin.

Definition

ChEBI: 3,5,7-trihydroxy-2-[3-(4-hydroxy-3-methoxyphenyl)-2-(hydroxymethyl)-2,3-dihydro-1,4-benzodioxin-6-yl]-3,4-dihydro-2H-1-benzopyran-4-one is a flavonolignan.

General Description

Silymarin is a flavonolignan, obtained from milk thistle (Silybum marianum) plant.

Biochem/physiol Actions

Silymarin was shown to protect the liver from the cytotoxic effects of anti-tuberculosis drugs by decreasing serum alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP) levels. This effect was related to the anti-oxidant effects of silymarin.

Mechanism of action

Silymarin is thought to protect the liver by preventing the entry of toxins into the hepatocyte and by stimulating nucleolar polymerase A, which, in turn, increases protein synthesis and liver regeneration. Silymarin undergoes enterohepatic circulation, increasing its concentration in hepatocytes. It is also an antioxidant in its own right and is considered to have some cytoprotective effect against carcinogens.

Mechanism of action

Silybum marianum (milk thistle) contains numerous phytocompounds, such as silymarin and silibinin, demonstrating antioxidant and anti-inflammatory activity. Silibinin has strong protection against UV-induced damage by inhibition in both cell proliferation and apoptosis by reducing thymine dimer-positive cells and upregulating p53 in mice. Increasing the transcriptional activity of p53 leads to the synthesis of p21/Cip1, a protein that arrests DNA synthesis and thereby increases DNA repair time.

Clinical Use

Alcoholic cirrhosis has been improved (faster return of liver enzymes to baseline) in at least three trials, although one multicenter Spanish study failed to demonstrate any change in the clinical course.There is no evidence to support the use of milk thistle to increase alcohol tolerance, although it is certainly being used for this purpose. The effectiveness of silymarin for viral hepatitis is not clear, although several trials demonstrated enough benefit to encourage further studies.
Intravenous silymarin has been demonstrated to lower mortality from Amanita mushroom poisonings, but this formulation is available only in Europe.Animal studies have demonstrated hepatic protection against alcohol, acetaminophen, and mushroom toxins and protection against hepatic fibrosis with bile duct occlusion. There is also evidence of silybin protecting against cisplatin- induced nephrotoxicity in rats. It is not yet clear whether milk thistle extract offers any renal protection to humans.

Side Effects

Milk thistle appears to be remarkably safe, with loose stools due to increased bile solubility and occasional allergic reactions being the common side effects. It has not been evaluated in children or in pregnant women.There are no known serious drug or herb interactions.

Toxicity evaluation

Silymarin has been known for its very low toxicity, Acute toxicity studies of silymarin after intravenous infusion have been carried out in mice, rats, rabbits and dogs. The LD50 values were 400 mg/kg in mice, 385 mg/ kg in rats, and 140 mg/kg in rabbits and dogs though these values were dependent on infusion rate. With slow infusion rate (over 2 to 3 h) the LD50 increased to 2 g/kg in rats and after oral administration it was even 10 g/kg.