Prevalidation of a Rat Liver Foci Bioassay (RLFB) Based on Results from 1600 Rats: A Study Report

Abstract

A rat liver foci bioassay (RLFB) based on an initiation-promotion protocol employing preneoplastic foci of altered hepatocytes (FAH) as an endpoint, was prevalidated in 5 different laboratories. FAH were identified by immunohistochemical demonstration of glutathione-S-transferase (placental form, GSTP) and by staining with hematoxilin/eosin (H&E), and their area fraction was quantified morphometrically. The four model hepatocarcinogens N-nitrosomorpholine, 2-acetylaminofluoren, phenobarbital, and clofibrate were selected according to characteristic differences in their presumed mode of action, and tested in a total of 1,600 male and female rats at 2 different dose levels. The chemicals were found to differ characteristically in their potency and dose-response relationship to induce FAH when given alone or when administered following initiation with diethylnitrosamine. The interlaboratory variation was small for results obtained with the GSTP-stain and somewhat larger with respect to H&E. The assessment of the carcinogenic potential of the four chemicals by the different laboratories was in the same range and the nature of their dose-response relationships did not differ essentially between laboratories. Our results suggest that this RLFB is a sensitive bioassay, providing potentially valuable information for risk assessment including the classification of carcinogenic chemicals according to their mode of action.

Altered methylation of specific DNA loci in the liver of Bhmt‐null mice results in repression of Iqgap2 and F2rl2 and is associated with development of preneoplastic foci

“…We examined the timing of initiation and proportion of liver expressing GST‐P activity, a marker for preneoplastic foci (27), in Bhmt ‐null compared with WT liver. At 4 wk, there was no difference in GST‐P staining (Fig.…”