Pharmacology of Silymarin

F. Fraschini, G. Demartini, D. Esposti,

Disclosures

Clin Drug Invest. 2002;22(1) 

In This Article

5. Antioxidant and Hepatoprotective Effects of Other Flavonoids

Flavonoids are a large group of phenolic compounds ubiquitously distributed in the plant kingdom. More than 4000 flavonoids belonging to different classes have been identified so far. They are important for the normal growth, development and defence of plants. Important constituents of the human diet, they are present in fruit and vegetables. Multiple biological effects of flavonoids have been described, including anti-inflammatory, antiallergic, antihaemorrhagic, anti-mutagenic, antineoplastic and hepatoprotective activities.[78] The biological and pharmacological effects of flavonoids in mammals are assumed to result mainly from two properties: modulation of certain enzymes (hexokinase, aldose reductase, phospholipase C, protein kinase C, cyclo-oxygenase, lipoxygenase, myeloperoxidase, NADPH oxidase and xanthine oxidase) and their antioxidant activity. The various flavonoids, however, vary greatly in their efficacy, and a single flavonoid can inhibit one enzyme at a certain concentration while inhibiting another enzyme at a 100-fold higher concentration.[46,47]

Some flavonoids, including quercetin and silibinin, can protect cells and tissues against the effects exerted by reactive oxygen species. Their antioxidant activity results from the scavenging of free radicals and other oxidising intermediates, from the chelation of iron or copper ions, and from inhibition of oxidases.[79] As discussed in the preceding sections, flavonoids from Silybum marianum have been widely used for the treatment of liver disorders. In experimental animal models they were demonstrated to exert not only a positive effect on intact liver cells or cells not yet irreversibly damaged, but also to stimulate their regenerative capacity after partial hepatectomy.[41]

Antihepatotoxic activity was also demonstrated for kolaviron, a defatted alcoholic extract of the seeds of Garcinia kola, and for Garcinia biflavonones, in mice intoxicated with phalloidin.[80] Other flavonoids extracted from Baccharis trimera were reported to protect mice from hepatic damage; hispidulin appeared to be the most active compound, and quercetin, luteolin, nepetin and apigenin were less active or inactive.[81] Quercetin, however, was demonstrated to exert some ameliorative effects on tissue damage induced by cigarette smoke[78] and to reduce the cytotoxic effect of T-2 mycotoxin.[82] Gossypin and hydroxyethyl rutosides significantly reduced the toxic effect of dermal application of sulphur mustard on hepatic lipid peroxidation in mice. Moreover, it increased the survival rate of the animals.[83]

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