Ultrastructural Cytochemistry of Eosinophilic Inclusions in the Cells of Hyperplastic Nodules and Hepatomas in Mouse Liver

Intracisternal inclusions in the cells of 48 hyperplastic nodules and hepatomas in mouse liver were examined by electron microscopy to determine the precise compositions of the inclusions in relation to their ultrastructure, and some preliminary attempts at isolation and chemical analysis of the inclusions were performed. We classified the inclusions into two types. One was mainly of larger size, consisting of a single electron-lucent core and a granular cortical zone of high electron density. The other type was smaller, with a number of tiny, electron-lucent areas crowded into the central area instead of a single core. The cortical material of the inclusions was digested by pepsin treatment of thin sections, whereas the core and the electron lucent areas within the cortical zone were not extracted. On the other hand, in materials treated with ethanol before post osmication, only the core and electron-lucent areas within the cortical zone were partially extracted. The ultrastructure of the isolated inclusions was very similar to that of inclusions in situ . The chemical composition of the isolated fractions was estimated to be 60% protein and 35% lipid. Electrophoretically, the protein of this fraction showed a single band. We conclude that the cortical substance is proteinaceous in nature, probably consisting of a single protein or a group of proteins with identical electrophoretic mobility, whereas the core is composed of lipid. The possibility that the inclusions are due to an impairment in the mechanism of intracellular lipoprotein transport is discussed.