Quantification of hepatocytic proliferation in the laboratory mouse

The proliferation rate in livers of 120 mice (60 males and 60 females) was analyzed by immunohistochemical detection of bromodeoxyuridine (BrdU) incorporation and proliferating cell nuclear antigen (PCNA) expression on ethanol-fixed/paraffin-embedded specimens. Mice were divided into three groups, with 20 males and 20 females in each group: mice in the first group served as controls, while mice in the second and third groups were treated with a low and a high dose, respectively, of a non-genotoxic drug candidate for 2 weeks. A dose-related increase of the proliferating hepatocyte fraction was disclosed by both immunohistochemical methods, reaching statistical significance already in the low-dose male group for BrdU incorporation and in both male and female low-dose groups for PCNA expression. A good correlation between the degree of BrdU and PCNA labeling was observed and, as expected, the percentage of PCNA expressing cells was generally higher than the percentage of BrdU-positive cells. We concluded that the detection of PCNA expression represents a reliable method for the quantification of the hepatocytic proliferating fraction in rodents and allows the use of archival material for cell kinetic investigations in toxicologic pathology.