Two important antioxidant enzymes in the heart are catalase and glutathione peroxidase (GPx). We have previously shown that cysteine incubation of isolated rat cardiomyocytes reduces reactive oxygen species (ROS) production during oxidative stress compared to non-cysteine incubated cells (Hall et al. J Physiol (2005), 567P PC15). This study investigates whether cysteine's cardioprotective effect was related to the activities of catalase and GPx. Assays were performed in suspensions of isolated rat cardiomyocytes following incubation at 37°C with or without (control) 0.5mM cysteine. GPx activity was significantly higher in cysteine incubated cells compared to control (1.24 ± 0.17 Units vs. 0.72 ± 0.14, p<0.05, n = 6 ± S.E.) whilst catalase activity was similar in each group. During 0.2mM H₂O₂ exposure, ROS production, measured as a percentage increase in fluorescence, was significantly lower in cysteine incubated cells (535.6 ±55.8%) compared to control cells (929.2 ± 40.1, p<0.01, n = 4 ±S.E.). 0.05mM mercaptosuccinic acid (GPx inhibitor), significantly increased ROS production in cysteine incubated cells (765.3 ± 38.7%vs. 880.6 ± 46.8% for control) These data suggest that incubating cardiomyocytes with 0.5mM cysteine helps to protect against oxidative stress by stimulating GPx.

Supported by the British Heart Foundation