Abstract 143: Catalase, Oxidative Stress and Ischemic Injury: Role of c-Abl Tyrosine Kinase

Abstract

Thousands of children with congenital heart disease are subjected to corrective surgery which involves stopping the heart and exposing it to ischemia reperfusion (IR) injury. Complications after cardiopulmonary bypass like low cardiac output can lead to inadequate organ perfusion and eventual organ dysfunction if not corrected in a timely manner. Newborn (2-4 days) hearts are more susceptible to ischemic injury than adult (>8 weeks) hearts as evidenced by their diminished ability to scavenge reactive oxygen species (ROS), specifically hydrogen peroxide (H 2 O 2 ). Not only do newborn hearts exhibit decreased scavenging capability (compared to the adult) but they also contain reduced baseline levels of catalase (3.8 + 1.1 U/mg tissue in the LV and 4.3 + 2.3 U/mg tissue in the RV vs. 11.2 + 1.0 U/mg tissue in the adult LV and 11.6 + 0.3 U/mg tissue in the adult RV). We observed significantly increased levels of H 2 O 2 in newborn rabbit myocytes following IR injury (4.3-fold vs 2.2 fold; p<0.05) that was not accompanied by an increase in catalase activity as was seen in the adult myocytes. The tyrosine kinase c-Abl was shown to play a role in regulating phosphyorylation (and activation) of catalase and we hypothesized this pathway may be dysregulated in newborns, leading to differences in catalase activity. We performed immunoprecipitation with c-Abl and catalase as well as Western analysis of whole heart homogenates in both newborn and adult samples (n=3). Results demonstrated an increase in catalase phosphorylation in adult but not newborn hearts after IR. In the newborn, preliminary studies displayed diminished phosphorylation of c-Abl, indicating a potential mechanism. In addition, catalase levels seem to acutely rise following IR, too early for new protein synthesis. Catalase is known to undergo ubiquitination following release from the c-Abl complex and this may play a role in the failure of newborns to increase catalase. Elucidation of this pathway will lead to a greater understanding of the mechanisms controlling catalase activity in the newborn versus the adult heart and will prove beneficial in developing therapeutic interventions to minimize damage following ischemic injury in newborns.