Experimental research on apoptosis induced following microwave coagulation therapy against liver cancer

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Microwave coagulation therapy (MCT), one of the local hyperthermia, has been widely performed to liver cancer patients, and yielded better clinical results than PEIT and TAE. In spite of the efficacy, the precise mechanism for expansion of cell death area following the therapy has still been unknown. The aim of this study was to understand the cellular mechanism of MCT focusing on whether the heat-induced apoptosis is occurred in the liver tissue by sequential examinations of caspase-3 activity and DNA fragmentation.One bout of MCT was applied to the rat liver using a monopolar needle electrode under setting of 30 W for 30 sec as coagulation time and 10 sec as dissociation time. The rats were sacrificed immediately, 2, 6, 12, 24, 72 and 168 h after MCT. The liver surface area was measured for evaluation of expansion of cell death area. For the assessment of the apoptosis, the TUNEL staining and the TUNEL positive cell counting was examined for the localization and the quantitiveness of DNA fragmentation. The caspase-3 activity in the specimen extracted from MCT site was measured for enzymatic evaluation of apoptosis.The caspase-3 activity showed four-fold increase from the value of 0 h, having a peak at 2 h after MCT. The DNA fragmentation significantly increased at 6 h, and decreased thereafter, assessed by the TUNEL positive cell count. The discolored liver surface area gradually increased until 12 h after MCT, sustained from 12 h to 72 h, and subsided thereafter.It was demonstrated following MCT that the apoptosis of hepatocytes was induced around the ablation area. This may explain the mechanism for the expansion of cell death area subsequent to MCT.