Silymarin as a new hepatoprotective agent in experimental cholestasis: new possibilities for an ancient medication

Silymarin is a purified extract from milk thistle (Silybum marianun (L.) Gaertn), composed of a mixture of four isomeric flavonolignans: silibinin (its main, active component), isosilibinin, silydianin and silychristin. This extract has been empirically used as a remedy for almost 2000 years, and remains being used as a medicine for many types of acute and chronic liver diseases. Despite its routinely clinical use as hepatoprotectant, the mechanisms underlying its beneficial effects remain largely unknown. This review addresses in detail a number of recent studies showing a novel feature of silymarin as a hepatoprotective drug, namely: its anticholestatic properties in experimental models of hepatocellular cholestasis with clinical correlate. For this purpose, this review will cover the following aspects: 1. The chemistry of silymarin, including chemical composition and properties. 2. The current clinical applications of silymarin as a hepatoprotective agent, including the mechanisms by which silymarin is thought to exert its hepatoprotective properties, when known. 3. The physiological events involved in bile formation, and the mechanisms of hepatocellular cholestasis, focusing on cellular targets and mechanisms of action of drugs used to reproduce experimentally cholestatic diseases of clinical interest, in particular estrogens and monohydroxylated bile salts, where anticholestatic properties of silymarin have been tested so far. 4. The recent findings describing the impact of silymarin on normal bile secretion and its novel, anticholestatic properties in experimental models of cholestasis, with particular emphasis on the cellular/molecular mechanisms involved, including modulation of bile salt synthesis, biotransformation/depuration of cholestatic compounds, changes in transporter expression/activity, and evocation of signaling pathways.