Striatal Neuron Death in Hypoxic-Ischemic Newborn Piglets is Non-Apoptotic and Evolves With Transient Mitochondrial Activation, Oxidative Injury, and Early Damage to DNA and the Golgi • 1885

Abstract

The mechanisms for striatal neurodegeneration following hypoxia-ischemia(HI) in newborns are not understood. We used a piglet model of HI to test the hypothesis that the progression of striatal neuron death is associated with ahnormal mitochondrial function and oxidative damage. Piglets (≈1 week old) were subjected to 30 min hypoxia (arterial O2 saturation 30%) and then 7 min of airway occlusion (O2 saturation 5%), producing asphyxic cardiac arrest, followed by CPR, return of spontaneous circulation, and then recovery for 3, 6, 12 or 24 hours (h). Neuronal damage in putamen was 16%, 31%, 47%, and 79% at 3, 6, 12, and 24 h, respectively. Ultrastructurally, vesiculation of Golgi and fragmentation of rough endoplasmic reticulum (RER) with dispersion of free ribosomes occurred at 3-6 h, while mitochondria appeared intact until 12 h. Most degenerating neurons (> 95%) had nonapoptotic cytoplasmic organelle damage and nonapoptotic chromatin clumping and nuclear condensation. In agarose gels, striatal DNA was randomly fragmented at 6-12 h. Biochemical assay of cytochrome oxidase (COX) activity in striatum revealed time-dependent changes in mitochondrial function; COX activity was 37%, 163%, 72%, and 81% of control at 3, 6, 12, and 24 h, respectively. Histochemical assay for COX in putamen revealed a similar temporal profile for transient mitochondrial activation and subsequent mitochondrial failure. Free radical damage to nuclear DNA in striatal neurons was detected as early as 3-6 h after HI with antibodies to 8-hydroxydeoxyguanosine. Using nitrotyrosine modification of proteins as a marker for peroxynitrite-mediated oxidative stress, nitrated proteins (≈45 and 68 kDa) in striatum were detected at 3-12 h. Neuronal nitric oxide synthase protein levels were unchanged by immunoblotting. We conclude that the transient burst of mitochondrial function between 3-6 h recovery is linked to free oxygen radical injury and rapid damage to nuclear DNA and membranous compartments such as the Golgi and RER. These data support an integrated mechanism for rapid neuronal necrosis in the striatum of HI newborns involving oxidative injury.