Silymarin protection against major reactive oxygen species released by environmental toxins: exogenous H2O2 exposure in erythrocytes.

Silymarin is a polyphenolic plant flavonoid (a mixture of flavonoid isomers such as silibinin, isosilibinin, silidianin and silichristin) derived from Silymarin marianum that has anti-inflammatory, hepatoprotective and anticarcinogenic effects. Our earlier studies have shown that silymarin plays a protective role against the oxidative damage induced by environmental contaminants like benzo(a)pyrene in erythrocyte haemolysates. During the detoxification of these environmental contaminants, the major reactive oxygen species generated is hydrogen peroxide (H(2)O(2)). Because H(2)O(2 )can easily penetrate into the cell and cause damage to biomolecules, the protective role of silymarin was further assessed against this cytotoxic agent in vitro in erythrocyte haemolysates. The protective effect was monitored by assessing the levels of the antioxidant enzymes superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glutathione-s-transferase, glutathione peroxidase and malondialdehyde (LPO) in three groups: vehicle control, H(2)O(2)-exposed groups and drug co-incubation group (H(2)O(2) + silymarin). The protective effect of silymarin on the non-enzymic antioxidant glutathione and haemolysis, methaemoglobin content and protein carbonyl content were also assessed. It was observed that the activities of antioxidant enzymes and glutathione were reduced and the malondialdehyde levels were elevated after H(2)O(2 )exposure. There were also alterations in haemolysis, methaemoglobin content and protein carbonyl content, whereas after the administration of silymarin, the antioxidant enzyme activities reversed to near normal with reduced malondialdehyde content and normalized haemolysis, methaemoglobin content and protein carbonyl content. The results suggest that silymarin possesses substantial protective effect and free radical scavenging mechanism against exogenous H(2)O(2)-induced oxidative stress damages, hence, can be used as a protective drug against toxicity induced by environmental contaminants.

Protective effect of silymarin on erythrocyte haemolysate against benzo(a)pyrene and exogenous reactive oxygen species (H2O2) induced oxidative stress.

The present study was carried out to evaluate the in vitro antioxidant properties and protective effects of silymarin (milk thistle) in human erythrocyte haemolysates against benzo(a)pyrene [B(a)P], a potent carcinogenic chemical. Protective effect of silymarin was assessed in vitro by monitoring the antioxidant enzymes and malondialdehyde in three groups of haemolysates-(I) vehicle control (II) B(a)P incubated group and (III) B(a)P co incubated with silymarin. The effects of silymarin on lipid peroxidation (LPO) and antioxidant enzymes [superoxide dismutase; SOD, catalase; CAT, glutathione peroxidase; GPx, glutathione reductase; GR and glutathione-S-transferases; GST] were assessed on haemolysates. It was observed that specific activity of antioxidant enzymes were significantly decreased and the malondialdehyde levels were elevated when haemolysates were incubated with B(a)P. The protective effect of silymarin is elucidated by the significant reversal of the antioxidant enzymes and reduction in the levels of malondialdehyde. In addition, haemolysates were incubated with B(a)P for 45 min and the B(a)P metabolite, 3-hydroxy benzo(a)pyrene (3-OH-B(a)P) was detected using HPLC. An increased level of the metabolite was detected in group II. Whereas, when haemolysates were co-incubated with silymarin, the reactive metabolite 3-OH-B(a)P was not detectable which further confirms the protective role of silymarin. Generation of 3-OH-B(a)P in group II implicates the possibility of reactive oxygen species (O2- and H2O2) production in haemolysates during cytochrome P4501A1 (CYP1A1) mediated Phase-I-metabolism. Hence, we incubated the haemolysates with exogenous reactive oxygen species H2O2 and assessed the protective role of silymarin against H2O2. From the results of our study, it was suggested that silymarin possess substantial protective effect and free radical scavenging mechanism against environmental contaminants induced oxidative stress damages.