OBJECTIVE Metallothionein (MT) has been previously shown to protect against doxorubicin (DOX)-induced cardiotoxicity, but underlying mechanism still remains poorly understood.DOX induces cardiac mitochondrial toxicity, including mitochondrial oxidative stress and inhibition of mitochondrial biogenesis.In the present study, we hypothesized that MT regulation of mitochondrial oxidative stress and biogenesis results in protection against DOX-induced cardiotoxicity.METHODS Adult male metallothionein-Ⅰ / Ⅱ-null (MT-/-) and wild type (MT +/+) mice were given a single administration of DOX (15 mg· kg-1, i.p.) or equal volume of normal saline.Four days after treatment, mice were sacrificed and hearts were collected for analysis including histopathological observation, oxidant-antioxidant status examination and biogenesis.Primary cultured cardiomyocytes from neonatal MT+/+ and MT-/-mice were treated with DOX to detect apoptosis, cellular ROS levels, mitochondrial ROS levels and mitochondrial membrane potential.RESULTS DOX was found to induce histopathological alteration in the hearts from both MT+/+ and MT-/-mice, with prominent ultrastructual changes in cardiac mitochondria.DOX increased cardiac apoptosis and caspase-3 activation, inhibited the activity of catalase and glutathione peroxides, induced mitochondrial oxidative injury including lipid peroxidation and protein carbonylation, and suppress PGC-1α-mediated mitochondrial biogenesis.DOX time-and concentration-dependently increased cellular ROS level in cultured cardiomyocytes.Furthermore, by using mitochondrial fluorescent probe, MitoSox Red and Rhodamine 123, the results indicate that DOX time-dependently induce increase of mitochondrial ROS generation and decrease of mitochondrial membrane potential.As compared to MT +/+ mouse heart or its cultured cardiomyocytes, all these changes were greater in MT-/-mouse heart or it cultured cardiomyocytes.CONCLUSION The present study suggests that basal MT provides protection against DOX-induced cardiotoxicity possibly by regulation of mitochondrial oxidation stress and biogenesis.