Detection of Higher-Order 50- and 10-kbp DNA Fragments before Apoptotic Internucleosomal Cleavage after Transient Cerebral Ischemia

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Abstract
DNA fragments of 50 and 10 kbp were found in ischemic brain in adult rats following two-vessel occlusion or in neonates following hypoxia–ischemia. These higher-order fragments were detected before any laddered oligonucleosomal DNA fragmentation characteristic of apoptosis. Both the 50- and 10-kbp fragments were also detected during necrosis produced by decapitation, but these led to smeared smaller fragments, not laddered patterns. End-group analysis showed the presence of both 3′-OH and 5′-OH ends in both the 50- and 10-kbp fragments but the predominance of 3′-OH ends in the laddered fragments. A higher proportion of 5′-OH to 3′-OH ends was found in the 10-kbp fragment compared to the larger 50-kbp fragment, suggesting a selective degradation of the 50-kbp DNA fragment to the laddered oligonucleosomal patterns. Overall, the mode of DNA fragmentation appeared different from that described in classic apoptosis of thymocytes.