Silibinin (INN), also known as silybin, is the major active constituent of silymarin, a standardized extract of the milk thistle seeds containing mixture of flavonolignans consisting of among others of silibinin, isosilibinin, silicristin, and silidianin

Silibinin (INN), also known as silybin, is the major active constituent of silymarin, a standardized extract of the milk thistle seeds containing mixture of flavonolignans consisting of among others of silibinin, isosilibinin, silicristin, and silidianin. Silibinin itself is mixture of two diastereomers silibinin A and silybinin B in approximately equimolar ratio. Both in vitro and animal research suggest that silibinin has hepatoprotective (antihepatotoxic) properties that protect liver cells against toxins.^[1][2] Silibinin has also demonstrated in vitro anti-cancer effects against human prostate adenocarcinoma cells, estrogen-dependent and -independent human breast carcinoma cells, human ectocervical carcinoma cells, human colon cancer cells, and both small and nonsmall human lung carcinoma cells.^[3][4][5][6]
Chemically modified silibinin, silibinin dihydrogen disuccinate disodium (trade name Legalon SIL) a solution for injection, is currently being tested as a treatment of severe intoxications with hepatotoxic substances, such as death cap (Amanita phalloides) poisoning.^[7] There is also clinical evidence for the use of silibinin as a supportive element in alcoholic and Child grade ‘A’ liver cirrhosis.^[8]

 FROM SILYBUM MARIANUM (L.) GAERTN.
A NEW NATURAL PREVENTIVE TARGETED AT THE LIVER
The liver, due to the vital role it plays in metabolism, is particularly exposed to the harmful action of endogenous and exogenous toxic substances. In fact, many potentially harmful molecules (alcohol, drugs, hormones, etc.) are metabolized by the liver and transformed into more hydro-soluble derivatives for subsequent biliary extraction and removal from the body. This detoxication process is achieved by a variety of enzymes (oxidizing, reducing, hydrolyzing or conjugating) located in the hepatic microsomes, part of the smooth endoplasmic reticulum of the liver cell. For this reason the upkeep of the integrity of the liver cell is necessary for the safeguarding of health. Several biochemical reactions involve as starters or intermediates various free radical species which constitute a continuous risk factor for the integrity of the hepatocytes.Therefore, any prevention aimed at reducing potential damage to the liver and any substances contributing to its integrity are certainly of interest. Derivatives of the traditionally used European plant Silybum marianum (L.) Gaertn. (Asteraceae) occupy an eminent position in liver protection. The name Silybum derives from "sillybon" (tuft, pendant), an ancient Greek word used by Dioscorides (I century A.D.) to indicate a thistle with white spotted leaves. An old legend tells that these white marks and stripes on the leaves represent the drops of Mary's milk fallen from her breast while she was breastfeeding Jesus during their escape to Egypt.² Since ancient times S. marianum has been known and used to be recommended as an emetic. During the Middle Ages the plant was probably cultivated in monasteries and used for medicinal purposes: the roots, herb and leaves were recommended for swelling and erysipelas (St. Hildegard from Bingen, 1098-1179) or for the treatment of liver complaints (Lonicerus, John Gerard, Pietro Andrea Mattioli, XVI-XVII centuries). From 1755 onwards, the specific use of S. marianum fruit for the treatment of liver disease, disorders of the bile duct and spleen was documented. At present, the standardized extract (silymarin) obtained from the fruit of S. marianum and containing as main constituents silybin, silydianin and silychristin (Fig.1), is widely used in European medicine in the treatment of liver disease. The main constituent silybin has been subjected to several biochemical and pharmacological studies which have demonstrated its interesting properties but also its poor bioavailability. Complexation with soy phosphatidylcholine gives rise to the lipophilic complex (US Patent 4, 764, 508) which substantially improves the bioavailibility of silybin. This results in a marked preventive action as observed in several models of liver intoxication including those with a strong involvement of oxidative stress. In this way, the silybin-phosphatidylcholine complex SILIPHOS®, containing 33% of silybin, endowed with antioxidant activity and, simultaneously, able to prevent cellular derangement by stabilizing the cell membranes and restoring the normal ultrastructure of the hepatocytes, plays a key role in the prevention of liver damage.http://www.swansonvitamins.com/health-library/products/siliphos.html

1. Al-Anati L, Essid E, Reinehr R, Petzinger E (2009). "Silibinin protects OTA-mediated TNF-alpha release from perfused rat livers and isolated rat Kupffer cells". Molecular Nutrition & Food Research 53 (4): 460–6. doi:10.1002/mnfr.200800110. PMID 19156713.
2. Jayaraj R, Deb U, Bhaskar AS, Prasad GB, Rao PV (2007). "Hepatoprotective efficacy of certain flavonoids against microcystin induced toxicity in mice". Environmental Toxicology 22 (5): 472–9. doi:10.1002/tox.20283. PMID 17696131.
3. Mokhtari MJ, Motamed N, Shokrgozar MA (2008). "Evaluation of silibinin on the viability, migration and adhesion of the human prostate adenocarcinoma (PC-3) cell line". Cell Biology International 32 (8): 888–92. doi:10.1016/j.cellbi.2008.03.019. PMID 18538589.
4. Bhatia N, Zhao J, Wolf DM, Agarwal R (1999). "Inhibition of human carcinoma cell growth and DNA synthesis by silibinin, an active constituent of milk thistle: comparison with silymarin". Cancer Letters 147 (1–2): 77–84. doi:10.1016/S0304-3835(99)00276-1. PMID 10660092.
5. Hogan FS, Krishnegowda NK, Mikhailova M, Kahlenberg MS (2007). "Flavonoid, silibinin, inhibits proliferation and promotes cell-cycle arrest of human colon cancer". Journal of Surgical Research 143 (1): 58–65. doi:10.1016/j.jss.2007.03.080. PMID 17950073.
6. Sharma G, Singh RP, Chan DC, Agarwal R (2003). "Silibinin induces growth inhibition and apoptotic cell death in human lung carcinoma cells". Anticancer Research 23 (3B): 2649–55. PMID 12894553.
7. Mitchell, T (2009). "Intravenous Milk thistle (silibinin-legalon) for hepatic failure induced by amatoxin/Amanita mushroom poisoning". (Clinical study).
8. Saller R, Brignoli R, Melzer J, Meier R (2008). "An updated systematic review with meta-analysis for the clinical evidence of silymarin". Forschende Komplementärmedizin (2006) 15 (1): 9–20. doi:10.1159/000113648. PMID 18334810. Retrieved 2010-12-14.