PRE-APOPTOTIC ALTERATIONS IN HEPATOCYTES OF TNF-ALPHA-TREATED GALACTOSAMINE-SENSITIZED MICE

Tumor necrosis factor (TNF) induces apoptotic death of hepatocytes in the galactosamine (GalN)-sensitized mouse liver after 5 hr. In our stu dy, the most remarkable sign of the early stage of apoptosis was the f ocal rupture of the outer mitochondrial membrane. Parts of the inner m embrane extended through the gap of the outer membrane, whereas the re st of the inner membrane still formed the cristae. This feature appear ed in hepatocytes before chromatin condensation. With the diaminobenzi dine technique for localization of cytochrome oxidase activity, the re action product was detectable by light and electron microscopy. Ten pe rcent of the hepatocytes were apoptotic, with condensed chromatin and high enzyme activity, 37% were pre-apoptotic, without chromatin conden sation but high enzyme activity, and 53% had neither condensed chromat in nor a remarkable reaction product of cytochrome oxidase activity. F as (APO-1, CD95) molecules on the plasma membrane of hepatocytes incre ased and were represented immunohistochemically in cells without chrom atin condensation. DNA strand breaks were also detectable before chrom atin aggregation. The results of this study indicate that mitochondria play a pivotal role in pre-apoptotic hepatocytes, together with an in crease of the Pas molecule on the plasma membrane and with the occurre nce of DNA strand breaks in the nucleus.