Formation of Nuclear Isopeptide in the Process of Neuronal Cell Death following Interstitial Hyperthermia in Normal Rat Brain

ABSTRACT

BACKGROUND: Radiofrequency (RF) interstitial hyperthermia has recently been shown to be a beneficial treatment modality for human malignant gliomas. It has also been shown that the thermal threshold dose for histopathological damage in the rat brain was heating at 41 degreesCfor 30 min. In the present study, we investigated apoptosis and necrosis of the neuronal cells in the brains of Fischer rats at different times after interstitial heating with lower than the thermal threshold dose. We also measured the isopeptide bond formation in neuronal cells showing apoptosis or necrosis. METHODS: The applicator needles of the RF interstitial heating device, connected to the Thermotron IV was applied to heat the brain at 39, 40, and 41 degreesCfor 30 minutes. Sham-heated control rats were treated the same as the heated rats. The sham-heated animals and those heated at 40 degreesCfor 30 min were sacrificed at 4, 72, 120, and 168 hours after heating, respectively, and the animals heated at 39 and 41 degreesCfor 30 minutes were sacrificed at 168 hours after heating. Coronally sectioned brain tissue, encompassing the heated lesions, were studied immunohistochemically for the expression of TGase1, TGase2, and TGase3, isopeptide. TUNEL assay was performed to examine apoptosis. RESULTS: Immunohistochemical studies showed that in the brains heated at 40 degreesCfor 30 minutes, necrosis with the maximal nuclear isopeptide-positive neuronal cells of the cerebral cortex were seen at 4 hours; The maximal number of isopep-tide- positive neuronal cells showing apoptosis was at 168 hours. CONCLUSIONS: Necrosis of neuronal cells following mild interstitial hyperthermia was maximal at 4 hours and apoptosis was maximal at 168 hours. Neuronal cells showing necrosis or apoptosis formed isopeptide bonds in their nuclei.