Advanced Nanotechnologies for Enhancing the Bioavailability of Silymarin: A State of the Art

Silymarin, a mixture of flavonolignan and flavonoid polyphenolic compounds extractable from milk thistle (Silybum marianum) seeds, is gaining an increasingly widespread clinical consensus as a natural remedy in the treatment of numerous chronic liver diseases such as cirrhosis and hepatocellular carcinoma due to its antioxidant, anti-inflammatory, anticancer and antiviral activities. Silymarin is able also to increase the stability of cell membrane, is active in the regeneration of tissues and prevents cardiac diseases through numerous mechanisms that include the action of chelating promoters of metals and scavenging free radicals. Equally promising are the effects of silymarin in protecting the brain from the inflammatory and oxidative stress effects by which metabolic syndrome contributes to neurodegenerative diseases. However, although clinical trials have proved that silymarin is safe at high doses (>1500 mg/day) in humans, it suffers limiting factors such as low solubility in water (<50 μg/mL) and low bioavailability. Furthermore, despite its poor solubility in water, silymarin does not retain lipophilic properties and this leads to poor intestinal permeability and rapid excretion in bile and urine. To potentiate the therapeutic action and promote sustained release of silymarin, numerous strategies have been proposed to tackle the low solubility in water and provide a prolonged drug release at the site of absorption. The purpose of this study is to review the different types of micro- and nanocarriers available in literature as delivery strategies to improve the intestinal absorption and bioavailability of silymarin.