Silymarin protects against doxorubicin induced cardiotoxicity by down-regulating topoisomerase II expression in mice

We investigated the potential protective effects of silymarin (SLY) on doxorubicin (DOX) induced chronic cardiotoxicity in mice. We used 30 male BALB/c mice assigned randomly to four experimental groups: control group administered normal saline orally daily and intraperitoneally (i.p.) twice/week during weeks 1, 2, 5 and 6; SLY group (was administered 100 mg/kg SLY daily by oral gavage for 6 weeks; DOX group was administered 3 mg/kg DOX i.p. twice/week during weeks 1, 2, 5 and 6; DOX + SLY group administered DOX and SLY corresponding to the DOX and SLY groups. At the end of the experiment, heart tissues were collected for analysis. Cardiomyopathy was observed in the DOX group; this damage was reduced by SLY treatment. SLY administration in DOX treated mice decreased topoisomerase II beta (TopII beta) expression as indicated by qPCR and immunostaining. Immunohistochemistry and western blot analysis revealed decreased phosphorylated histone-2AX (gamma H(2)Ax) expression in the SLY + DOX group. SLY administration combined with DOX increased cardiac troponin T and I (cTnT and cTnI) expression based on immunohistochemical and western blot analyses. SLY administration with DOX was cardioprotective by reducing double-strand DNA breakage by blocking the DOX-TopII beta-DNA cleavage complex in response to down-regulation of TopII beta expression. SLY also preserved the contractility of the heart by decreasing DOX related loss of cTnT and cTnI expression.