Assessment of peroxisome proliferation and liver growth-stimulating potential by nondirectly genotoxic compounds in cultured hepatocytes.

Previously, we have established that some peroxisome proliferators, a class of nongenotoxic hepatocarcinogens, are able to induce replicative DNA synthesis (RDS) in cultured hepatocytes. Hepatomegaly observed after short-term in vivo treatment correlated better with the ability to induce RDS than with the potency as peroxisome proliferator assessed in vitro. To clarify the challenging question of the limited sensitivity of primates to peroxisome proliferators, primary cultures of marmoset hepatocytes have been treated with nafenopin for some days. As expected from in vivo observations, no evidence for peroxisome proliferation could be observed. However, nafenopin induced a dose-dependent increase in the amount of RDS, but this induction was measurable only when the serum was absent from the culture medium. These results confirm that peroxisome proliferation and mitogenicity might be independent properties of peroxisome proliferators. Since in vivo the ability of compounds to induce RDS in liver cells is relevant to at least one key parameter of the hepatocarcinogenic response, it is suggested that measurement of RDS inducibility in cultured hepatocytes from different species might be relevant and useful to assess species differences in the liver tumor potency of nondirectly genotoxic compounds.