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Silymarin, an extract of flavonolignans from the dried fruits of milk thistle (Silybum marianum L. Gaertneri) and its constituents silibinin, dehydrosilibinin, silychristin and silydianin were tested for protective effects on rat cardiomyocytes exposed to doxorubicin. Silymarin and individual flavonolignans did not exert cytotoxicity in the range 25–100 µm (incubation 9 h). Dehydrosilibinin was tested only at 25 µm concentration due to its low solubility. All substances increased the cell ATP level. Silymarin and flavonolignans displayed a dose-dependent cytoprotection against doxorubicin (100 µm, incubation 8 h). The protective effects of silymarin, silibinin, dehydrosilibinin and silychristin were comparable to that of dexrasoxane, while silydianin exerted the best protective effect. The ability of silymarin complex and its components to protect cardiomyocytes against doxorubicin-induced oxidative stress is due mainly to their cell membrane stabilization effect, radical scavenging and iron chelating potency. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

To assess the role of plasma lipoproteins in the transport of silibinin, an antioxidant flavonolignan, 125I-labelled silibinin (125I-SB) administered perorally to the rat was used. The plasma 125I-SB derived radioactivity was distributed among plasma lipoproteins according to their lipophilicity (TAG-rich lipoproteins 30–40% > LDL 15% > HDL 5%), and in the fraction of d > 1.215 containing albumin and other proteins a minority amount of radioactivity was found. Administration of 125I-SB in a complex with phosphatidylcholine resulted in proportionally higher radioactivities in all fractions as well as in tissues. Dietary olive oil had a slightly decreasing effect on plasma concentrations of silibinin measured by HPLC as well as on 125I-SB derived radioactivity in plasma and liver. In the TAG-rich lipoprotein fraction and HDL no effects of olive oil on the levels of 125I-SB derived radioactivities were observed, however, at a 30 min interval the levels of 125I-SB derived radioactivity in LDL and the heart were significantly decreased in the olive oil group. These results suggest that (i) silibinin is not resorbed by the chylomicron pathway, and (ii) the endogenous lipoprotein pathway VLDL → LDL may play a role in the transport of silibinin from the liver to the extrahepatic tissues concurrently facilitating the lipoprotein antioxidant influence of silibinin. Copyright © 2003 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]