Thrombopoictin Protects Against Cardiotoxicity Induced By Doxorubicin.

Abstract Doxorubicin (DOX), an anthracycline drug, is the key component of various chemotherapy regimens. However, it exerts severe cardiotoxicity including cardiomyopathy and congestive heart failure. Thrombopoietin (TPO) is an established cytokine for promoting early hematopoietic progenitor cells, the megakaryocytic/platelet lineage and angiogenesis. In this study, we investigated effects of TPO on the protection against cardiotoxicity induced by DOX in a mouse model. Male Balb/c mice at 10 weeks of age were randomly divided into 3 groups (each N=6): Normal control (saline), DOX (20mg/kg, single dose i.p., Day 0) and TPO+DOX treatment (12.5μg/kg TPO at Days −1, +1 and +3). Transthoracic echocardiography (Sonos 7500) was performed using a high frequency transducer (15L6) at baseline (Day −1) and Day +5 on animals maintained at a conscious state. Our results demonstrated that DOX exerted cardiotoxicity in DOX-treated animals, indicated by significant reductions in heart weight, heart rate and fraction shortening (Table). Treatment with TPO significantly increased these heart function parameters. Effects of TPO were confirmed by the morphology of heart tissues, which demonstrated extensive cytoplasmic vacuolization (mean±SD = 20.0±3.30%) and myofibrillar loss (42.0±5.90%) in DOX-treated animals. These damages were significantly reduced in TPO+DOC-treated mice (8.00±1.60% and 21.0±3.30% respectively, p<0.05). The possible direct effects of TPO on rat cardiomyocytes were further investigated by in vitro studies on cell line and primary cells. The MTT assay on the H9C2 cell line demonstrated that DOX (5μg/ml, 24h) significantly reduced cell viability by 26.2±1.09% (n=4, p<0.01). These cells responded to TPO at a dose-dependent manner and cell viability was recovered to 85.6±4.43% (100ng/ml TPO, p<0.01). DOX (0.58μg/ml) inhibited primary neonatal cardiomyocytes in culture (48h) by reducing their beating rates to 9.25±11.1% of those recorded before DOX treatment (n=8, p<0.01). TPO and the cardioprotective drug dexrazoxane (5.8μg/ml) increased the beating rates of these cardiomyocytes to 47.8±12.7% and 34.5±11.5%, respectively (p<0.01). We also detected the expression of TPO receptors (c-mpl) by RT-PCR in mouse heart tissues. Our study demonstrated that TPO has cardioprotective effects against DOX toxicity and could be further developed for clinical applications. Effects of TPO on Heart Weight and Functions of DOX-Treated Mice Heart Weight (mg) Heart Rate (beats/min) Fraction Shortening (%) Mean±S.D.; * p<0.01 (DOX vs Control); # p<0.05 (DOX vs TPO+DOX at Day+5); ** p<0.05 (Day-1 vs Day+5) Control (Day-1) - 551±41.0 57.0±4.30 Control (Day+5) 118±15.3 581±40.0 60.7±2.80 DOX (Day-1) - 605±37.3 58.7±1.53 DOX (Day+5) 79.2±8.17* 410±45.2** 39.5±4.93** TPO+DOX (Day-1) - 575±40.0 60.2±3.55 TPO+DOX (Day+5) 92.7±6.94# 515±67.0# 56.3±7.66#