Atividades antimutagênica, antigenotóxica e anticitotóxica de Silybum marianum (L.) Gaertn e sua influência na expressão de genes de resposta a danos no DNA
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2015-03-26
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Universidade Federal de Goiás
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Silymarin (SM) is a standardized extract from the seeds and leaves of milk thistle Silybum marianum (L.) Gaertn. It is composed mainly of flavonolignans, with silibinin (SB) being its principal active constituent. Known mainly as antioxidant and hepatoprotector, SM and SB were found to be clinically effective in the treatment of a variety of liver disorders, including acute and chronic viral hepatitis, toxin and drug-induced hepatitis and cirrhosis. Due to the wide biological activities presented by SM and SB, the present study aimed to evaluate their antimutagenic activities using the Ames mutagenicity test in Salmonella typhimurium, their antigenotoxic activities using the mouse bone marrow micronucleous test and the alkaline comet assay, and to assess their effect on the gene expression pattern of some genes associated with the process of carcinogenesis and chemoprevention. To assess antimutagenicity, bacterial suspensions of Salmonella typhimurium (TA98 and TA100 strains) were treated with different concentrations of SM or SB simultaneously with the appropriate positive controls for each strain. To assess antigenotoxicity, Swiss mice were orally treated with different concentrations of SM or SB simultaneously with a single intraperitoneal dose of mitomycin C (MMC) for the micronucleus test, and human blood lymphocytes were cotreated with SM or SB and methyl methanesulfonate (MMS) for the alcaline comet assay. To investigate the role of SM and SB in modulating gene expression, we conducted microarray analysis. The results showed that SM was not significantly effective in reducing the number of frameshift mutations in strain TA98, while SB demonstrated significant protection at higher doses (p < 0.05). Regarding strain TA 100, SM and SB significantly decreased mutagenicity (point mutations) (p < 0.05). The results of the antigenotoxic evaluation demonstrated that SM and SB significantly reduced the frequency of micronucleated polychromatic erythrocytes (MNPCE) (p < 0.05). The results also indicated that SM and SB significantly attenuated MMC induced cytotoxicity (p < 0.05). In the comet assay, SM and SB significantly reduced the genotoxicity of MMS (p < 0.05), with a stronger antigenotoxic activity exerted by the extract complex (SM) than the one exerted by the isolated main active constituent (SB). The expression array analysis of five genes related to DNA damage, carcinogenesis and/or chemoprevention mechanisms demonstrated an up-regulation of PTEN and BCL2, down-regulation of BAX and ABL1 and no significant change in ETV6 expression levels.In conclusion, our results demonstrated that both SM and SB presented antimutagenic and antigenotoxic actions, as well as modulated the expression levels of genes analysed under the experimental conditions of this study.
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BORGES, F. F. V. Atividades antimutagênica, antigenotóxica e anticitotóxica de Silybum marianum (L.) Gaertn e sua influência na expressão de genes de resposta a danos no DNA. 2015. 123 f. Tese (Doutorado em Biologia) - Universidade Federal de Goiás, Goiânia, 2015.