Detection of higher-order 50- and 10-kbp DNA fragments before apoptotic internucleosomal cleavage after transient cerebral ischemia.

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.