Ischemic Cardiomyopathy Affects the Thioredoxin System in the Human Myocardium

Background: Oxidative damage as well as impaired proteasomal activity is believed to facilitate the process of ischemic (ICM) and dilated cardiomyopathy (DCM). The thioredoxin system is balancing the production of reactive oxygen species (ROS), inhibiting pathways of intrinsic apoptosis and regulating transcription factors. The present study investigated the changes of the thioredoxin system in ICM- and DCM-damaged human myocardium.

Methods: Myocardial tissue was obtained from residual material of ventricular assist device implantation or Morrow resection of patients suffering from ICM (n = 13), DCM (n = 13) or from septal tissue (control, n = 12). Protein expression of ITCH, TXNIP and thioredoxin was quantified by western blot. NADPH-oxidase activity assay was performed. Pro- and antiapoptotic markers (cCasp3, Casp 8, Casp9, PARP1, Akt, Bad, Bcl2, JNK p53), the concentration and activity of TXNRD1 were determined by multiplexing and ELISA.

Results: Compared with control, expression levels of ITCH (ICM: 0.32 ± 0.12, DCM: 0.66 ± 0.47, control: 0.70 ± 0.23, p = 0.006) and thioredoxin (ICM: 0.84 ± 0.34, DCM: 1.05 ± 0.41, control: 1.36 ± 0.36, p = 0.027) were reduced in ICM and DCM. TXNIP (ICM: 1.86 ± 1.08, DCM: 1.01 ± 0.38, control: 0.82 ± 0.22, p = 0.009) was increased in ICM, but not in DCM. Compared with control, ICM patients showed lower concentrations of TXNRD1 (ICM: 0.06 ± 0.02, DCM: 0.07 ± 0.02, control: 0.08 ± 0.02, p = 0.035) and activity of TXNRD1 (ICM: 0.0005 ± 0.0003a.U, DCM: 0.0007 ± 0.0001 a.U., control: 0.0009 ± 0.0002a.U., p = 0.005). DCM patients showed an increased cytochrome c release (ICM: 1476 ± 970ng/ml, DCM: 2313 ± 1300ng/ml, control: 1286 ± 667ng/ml, p = 0.065), caspase 9 expression (ICM: 582 ± 262MFI DCM: 1251 ± 548MFI, control: 561 ± 214ng/ml, p < 0.001) and NADPH-oxidase activity (ICM: 0.15 ± 0.03mU/mg, DCM: 0.35 ± 0.09mU/mg, control: 0.29 ± 0.04mU/mg, p = 0.030). Slightly increased p53 levels were detected in DCM compared with control (ICM: 47.3 ± 16.6MFI, DCM: 52.3 ± 18.2MFI, control: 37.7 ± 10.7MFI, p = 0.092).

Conclusion: ICM, but not DCM showed an impaired thioredoxin system in myocardial tissue. However, an increased ROS production as well as ROS-induced mitochondrial instability was detected in the DCM-damaged myocardium. Mitochondrial instability caused p53-induced apoptosis via caspase activation in DCM. Our results implicate that different cellular processes are impaired in DCM and ICM. Therefore, therapeutic strategies to treat and minimize the myocardial damage in DCM and ICM should differ.