DNA fragmentation indicative of apoptosis following unilateral cerebral hypoxia-ischemia in the neonatal rat

Dexamethasone prevents apoptosis in a neonatal rat model of hypoxic-ischemic encephalopathy (HIE) by a reactive oxygen species-independent mechanism

It has previously been shown, in a neonatal rat model of hypoxic-ischemic encephalopathy (HIE), that neuronal injury can be attenuated by pretreatment with dexamethasone. The mechanism by which dexamethasone exerts this protective effect is not known. Using the same neonatal rat model of HIE, we found pretreatment with dexamethasone to have no effect on the generation of superoxide radical, products of lipid peroxidation, peroxynitrite-mediated tissue damage or bcl-2 protein expression. However, dexamethasone did inhibit the induction of c-fos transcription seen following HIE, and subsequent evidence of apoptosis. We conclude that it is possible to limit hypoxic-ischemic neuronal injury, despite the continued production of reactive oxygen species, by interventions which block the cascade of events culminating in apoptosis. The involvement of apoptosis in the neuronal injury of HIE, if confirmed in acutely asphyxiated human infants, suggests that there may be a post-injury 'window of opportunity' for neuroprotective interventions.

A bcl-2 expressing viral vector protects cortical neurons from excitotoxicity even when administered several hours after the toxic insult

The product of the bcl-2 oncogene has been shown to play an important role in apoptosis and programmed cell death. In this study, a herpes simplex virus type-1 vector was constructed to carry the human bcl-2 gene. The possible role of bcl-2 in protecting neurons from excitoxicity was investigated by using the viral vector to deliver the gene into neuronal cultures before or after the cells were exposed to glutamate under conditions in which 50-80% of neurons died. Infection with the bcl-2 expressing vector 24 h prior to glutamate treatment effectively prevented the cell death that normally follows this treatment. Moreover, infection with the vector as late as 8 h after the glutamate insult still resulted in substantial neuroprotective effects. These results have potential implications for new therapies in stroke or ischemic neuropathies.

Cell death in the normal developing brain, and following ionizing radiation, methyl-azoxymethanol acetate, and hypoxia-ischaemia in the rat

Naturally occurring (programmed) cell death in the developing brain has morphological characteristics of apoptosis and is associated with internucleosomal DNA fragmentation. Apoptosis also plays a role in cell death following hypoxia-ischaemia in the developing rat brain. Ionizing radiation-induced cell death in the brain of the young rat has morphological characteristics of apoptosis, is mediated by protein synthesis and is associated with internucleosomal DNA fragmentation. Methyl-azoxymethanol (MAM) acetate injection in the young rat produces apoptotic cell death in the external granule cell layer of the cerebellum. In addition, strong c-Jun immunore-activity is observed in apoptotic cells during normal development and following experimentally induced cell death. Moreover, c-Jun mRNA induction and de novo c-Jun protein synthesis, together with activation of c-Jun/AP-1, as revealed with gel mobility shift assay, occurs in irradiated animals. Western blotting of total brain homogenates shows a c-Jun-immunoreactive band at p39, which corresponds to the molecular weight of c-Jun, in control rats. However, a thick c-Jun-immunoreactive band at about p62, accompanied by a decrease of the p39 band, occurs in irradiated and MAM-treated rats. A thin band immediately above the thick p62 band, suggestive of c-Jun phosphorylation, is also observed in treated rats. Taken together, these observations indicate that c-Jun expression is associated with apoptotic cell death in the developing central nervous system.