Nucleolar segregation as an early marker for DNA damage; an experimental study in rats treated with 4-hydroxyaminoquinoline 1-oxide.

Male 6-week-old Sprague Dawley rats were given a single intravenous injection of 4-hydroxyaminoquinoline 1-oxide (4HAQO) at a dose of 20 mg/kg in order to produce ultrastructural changes as possible morphological biomarkers for toxicity. Immunohistochemically demonstrated formation of 4HAQO-DNA adduct was correlated with the changes found. Nucleolar alteration, demonstrable by electron microscopy as segregation of nucleolar components into granular and fibrillar compartments, was evident in cells of the target organs, exocrine pancreas and adrenocortex, but not of the non-target liver parenchyma. Sequential observation clarified that such alteration was highest in frequency 6 h and 4 h after 4HAQO administration in pancreatic acinar cells and adrenocortical cells respectively. Electron microscopically, apoptotic changes of acinar cells were evident 2 h after injection of 4HAQO. DNA adduct formation was consistently demonstrated in the same target organs showing nucleolar segregation, the highest frequency being noted 4 h after 4HAQO treatment in both pancreatic acinar cells and adrenocortical cells. Our results thus indicate an identity of the target cells for nucleolar segregation and 4HAQO-DNA adduct formation which correlates with 4HAQO-toxicity. We suggest that nucleolar segregation occurs subsequent to the generation of DNA damage.