Increased cytochrome c in rat cerebrospinal fluid after cardiac arrest and its effects on hypoxic neuronal survival

Cerebrospinal fluid (CSF) proteins may be useful biomarkers of neuronal death and ultimate prognosis after hypoxic-ischemic brain injury. Cytochrome c has been identified in the CSF of children following traumatic brain injury. Cytochrome c is required for cellular respiration but it is also a central component of the intrinsic pathway of apoptosis. Thus, in addition to serving as a biomarker, cytochrome c release into CSF may have an effect upon survival of adjacent neurons. In this study, we use Western blot and ELISA to show that cytochrome c is elevated in CSF obtained from pediatric rats following resuscitation from cardiac arrest. Using biotinylated human cytochrome c in culture media we show that cytochrome c crosses the cell membrane and is incorporated into mitochondria of neurons exposed to anoxia. Lastly, we show that addition of human cytochrome c to primary neuronal culture exposed to anoxia improves survival. To our knowledge, this is the first study to show cytochrome c is elevated in CSF following hypoxic ischemic brain injury. Results from primary neuronal culture suggest that extracellular cytochrome c is able to cross the cell membrane of injured neurons, incorporate into mitochondria, and promote survival following anoxia.