Effect of the flavanolignans of Silybum marianum L. on lipid peroxidation in rat liver microsomes and freshly isolated hepatocytes.
The effect of several flavanolignans (silicristin, silidianin, silybin and isosilybin) present in silymarin, the extract of Silybum marianum fruits, was tested on lipid peroxidation in rat liver microsomes and freshly isolated hepatocytes. In microsomes lipid peroxidation was generated by ADP/Fe2+ and NADPH. All flavanolignans inhibited peroxidation in a concentration dependent manner. In hepatocytes lipid peroxidation was induced by ADP/Fe3+ complex and cell damage was evaluated as LDH activity released in the medium. The inhibition of the peroxidative process by flavanolignans was also evident in this model, even if with a potency order different from that found in microsomes. In contrast, the effect on LDH release was significant only for silybin and isosilybin, the other compounds being inactive on this parameter.
Pharmacol Res. 1992 Feb-Mar;25(2):147-54
The effects of silymarin on experimental phalloidine poisoning.
The hepatoprotective action of silymarin, the active principle extracted from the fruit of Silybum marianum (L.) Gaertn., in animals (dogs, rabbits, rats, mice) intoxicated with phalloidine is evident, both after protective and curative treatment. A dose of 15 mg/kg of silymarin protects every animal when given 60 minutes before the toxin. When injected 10 minutes after phalloidine, a dose of 100 mg/kg of silymarin again provides total protection. However, as the time span between administration of the toxic substance and start of treatment increases, so the efficacy of silymarin decreases; after 30 minutes its curative effect is negligible. The histochemical and histoenzymological studies show that during intoxication of the mice by phalloidine, silymarin inhibits the effect of the toxic substance and regulates the functions of the hepatocyte, when given either 60 minutes before or 10 minutes after phalloidine.
Arzneimittelforschung. 1975 Jan;25(1):89-96
Selectivity of silymarin on the increase of the glutathione content in different tissues of the rat.
Silymarin, a flavonoid extracted from the seeds of the milk thistle, Silybum marianum, increases the redox state and the total glutathione content of the liver, intestine, and stomach of the rat. The same treatment does not affect the levels of the tripeptides in the kidney, lung and spleen. This selective effect of the flavonoid on the digestive organs is ascribed to its pharmacokinetics on the digestive track, where the biliary concentration of silymarin is increased and maintained via the entero-hepatic circulation.
Planta Med. 1989 Oct;55(5):420-2
Scavenging of reactive oxygen species and inhibition of arachidonic acid metabolism by silibinin in human cells.
The effects of the flavonoid silibinin, which is used for the treatment of liver diseases, on the formation of reactive oxygen species and eicosanoids by human platelets, white blood and endothelial cells were studied. Silibinin proved to be a strong scavenger of HOCI (IC50 7 microM), but not of O2- (IC50 > 200 microM) produced by human granulocytes. The formation of leukotrienes via the 5-lipoxygenase pathway was strongly inhibited. In human granulocytes IC50-values of 15 microM and 14.5 microM silibinin were detected for LTB4 and LTC4/D4/E4/F4 formation, respectively. In contrast to this, three- to fourfold silibinin concentrations were necessary to half maximally inhibit the cyclooxygenase pathway. For PGE2 formation by human monocytes an IC50-value of 45 microM silibinin was found. IC50-values of 69 microM and 52 microM silibinin were determined for the inhibition of TXB2 formation by human thrombocytes and of 6-K-PGF1 alpha formation by human omentum endothelial cells, respectively. Thus, the deleterious effects of HOCI that can lead to cell death, and those of leukotrienes that are especially important in inflammatory reactions, can be inhibited by silibinin in concentrations that are reached in vivo after the usual clinical dose. Silibinin is thought not only to display hepatoprotective properties but might also be cytoprotective in other organs and tissues.
Life Sci. 1996;58(18):1591-600
Scavenging of reactive oxygen species by silibinin dihemisuccinate.
Silibinin dihemisuccinate (SDH) is a flavonoid of plant origin with hepatoprotective effects which have been partially attributed to its ability to scavenge oxygen free radicals. In the present paper the antioxidant properties of SDH were evaluated by studying the ability of this drug to react with relevant biological oxidants such as superoxide anion radical (O2-), hydrogen peroxide (H2O2), hydroxyl radical (HO.) and hypochlorous acid (HOCl). In addition, its effect on lipid peroxidation was investigated. SDH is not a good scavenger of O2- and no reaction with H2O2 was detected within the sensitivity limit of our assay. However, it reacts rapidly with HO. radicals in free solution at approximately diffusion-controlled rate (K = (1.0-1.2) x 10(10)/M/sec) and appears to be a weak iron ion chelator. SDH at concentrations in the micromolar range protected alpha 1-antiproteinase against inactivation by HOCl, showing that it is a potent scavenger of this oxidizing species. Luminol-dependent chemiluminescence induced by HOCl was also inhibited by SDH. The reaction of SDH with HOCl was monitored by the modification of the UV-visible spectrum of SDH. The studies on rat liver microsome lipid peroxidation induced by Fe(III)/ascorbate showed that SDH has an inhibitory effect, which is dependent on its concentration and the magnitude of lipid peroxidation. This work supports the reactive oxygen species scavenger action ascribed to SDH.
Biochem Pharmacol. 1994 Aug 17;48(4):753-9
The effect of silibinin (Legalon) on the the free radical scavenger mechanisms of human erythrocytes in vitro.
The effect of Legalon was investigated parallel with that of Adriblastina (doxorubicin) and paracetamol on some parameters characterizing the free radical scavenger mechanisms of human erythrocytes in vitro and on the time of acid hemolysis performed in aggregometer. Observations suggest that Adriblastina enhances the lipid peroxidation of the membrane of red blood cells, while paracetamol causes significant depletion of intracellular glutathione level, thus decreasing the free radical eliminating capacity of the glutathione peroxidase system. Legalon on the other hand, is able to increase the activity of both superoxide dismutase and glutathione peroxidase, which may explain the protective effect of the drug against free radicals and also the stabilizing effect on the red blood cell membrane, shown by the increase of the time of full haemolysis.
Acta Physiol Hung. 1992;80(1-4):375-80
Inhibition of Kupffer cell functions as an explanation for the hepatoprotective properties of silibinin.
The flavonoid silibinin, the main compound extracted from the milk thistle Silybum marianum, displays hepatoprotective properties in acute and chronic liver injury. To further elucidate the mechanisms by which it acts, we studied the effects of silibinin on different functions of isolated rat Kupffer cells, namely the formation of superoxide anion radical (02-), nitric oxide (NO), tumor necrosis factor alpha (TNF-alpha), prostaglandin E(2) (PGE(2)), and leukotriene B(4) (LTB(4)). Production of 02- and NO were inhibited in a dose-dependent manner, with an 50 percent inhibitory concentration (IC(50)) value around 80 micro mol/L. No effect on TNF-alpha formation was detected. Opposite effects were found on the cyclooxygenase and 5-lipoxygenase pathway of arachidonic acid metabolism. Whereas no influence on PGE(2) formation was observed with silibinin concentrations up to 100 micro mol/L, a strong inhibitory effect on LTB(4) formation became evident. The IC(50)-value for inhibiting the formation of this eicosanoid was determined to be 15 micro mol/L silibinin. The strong inhibition of LTB(4), formation by silibinin was confirmed in experiments with phagocytic cells isolated from human liver. Hence, while rather high concentrations of silibinin are necessary to diminish free radical formation by activated Kupffer cells, significant inhibition of the 5-lipoxygenase pathway already occurs at silibinin concentrations which are achieved in vivo. Selective inhibition of leukotriene formation by Kupffer cells can at least partly account for the hepatoprotective properties of silibinin.
Hepatology. 1996 Apr;23(4):749-54
Long-term (12 months) treatment with an anti-oxidant drug (silymarin) is effective on hyperinsulinemia, exogenous insulin need and malondialdehyde levels in cirrhotic diabetic patients.
BACKGROUND/AIMS: Several studies have demonstrated that diabetic patients with cirrhosis require insulin treatment because of insulin resistance. As chronic alcoholic liver damage is partly due to the lipoperoxidation of hepatic cell membranes, anti-oxidizing agents may be useful in treating or preventing damage due to free radicals. The aim of this study was to ascertain whether long-term treatment with silymarin is effective in reducing lipoperoxidation and insulin resistance in diabetic patients with cirrhosis. METHODS: A 12-month open, controlled study was conducted in two well-matched groups of insulin-treated diabetics with alcoholic cirrhosis. One group (n=30) received 600 mg silymarin per day plus standard therapy, while the control group (n=30) received standard therapy alone. The efficacy parameters, measured regularly during the study, included fasting blood glucose levels, mean daily blood glucose levels, daily glucosuria levels, glycosylated hemoglobin (HbA1c) and malondialdehyde levels. RESULTS: There was a significant decrease (p<0.01) in fasting blood glucose levels, mean daily blood glucose levels, daily glucosuria and HbA1c levels already after four months of treatment in the silymarin group. In addition, there was a significant decrease (p<0.01) in fasting insulin levels and mean exogenous insulin requirements in the treated group, while the untreated group showed a significant increase (p<0.05) in fasting insulin levels and a stabilized insulin need. These findings are consistent with the significant decrease (p<0.01) in basal and glucagon-stimulated C-peptide levels in the treated group and the significant increase in both parameters in the control group. Another interesting finding was the significant decrease (p<0.01) in malondialdehyde/levels observed in the treated group. CONCLUSIONS: These results show that treatment with silymarin may reduce the lipoperoxidation of cell membranes and insulin resistance, significantly decreasing endogenous insulin overproduction and the need for exogenous insulin administration.
J Hepatol. 1997 Apr;26(4):871-9
Silibinin decreases prostate-specific antigen with cell growth inhibition via G1 arrest, leading to differentiation of prostate carcinoma cells: implications for prostate cancer intervention.
Reduction in serum prostate-specific antigen (PSA) levels has been proposed as an endpoint biomarker for hormone-refractory human prostate cancer intervention. We examined whether a flavonoid antioxidant silibinin (an active constituent of milk thistle) decreases PSA levels in hormone-refractory human prostate carcinoma LNCaP cells and whether this effect has biological relevance. Silibinin treatment of cells grown in serum resulted in a significant decrease in both intracellular and secreted forms of PSA concomitant with a highly significant to complete inhibition of cell growth via a G1 arrest in cell cycle progression. Treatment of cells grown in charcoal-stripped serum and 5alpha-dihydrotestosterone showed that the observed effects of silibinin are those involving androgen-stimulated PSA expression and cell growth. Silibinin-induced G1 arrest was associated with a marked decrease in the kinase activity of cyclin-dependent kinases (CDKs) and associated cyclins because of a highly significant decrease in cyclin D1, CDK4, and CDK6 levels and an induction of Cip1/p21 and Kip1/p27 followed by their increased binding with CDK2. Silibinin treatment of cells did not result in apoptosis and changes in p53 and bcl2, suggesting that the observed increase in Cip1/p21 is a p53-independent effect that does not lead to an apoptotic cell death pathway. Conversely, silibinin treatment resulted in a significant neuroendocrine differentiation of LNCaP cells as an alternative pathway after Cip1/p21 induction and G1 arrest. Together, these results suggest that silibinin could be a useful agent for the intervention of hormone-refractory human prostate cancer.
Proc Natl Acad Sci U S A. 1999 Jun 22;96(13):7490-5