Toxicity monitoring with primary cultured hepatocytes underestimates the acetaminophen-induced inlammatory responses of the mouse liver

In vitro gene expression proiling with isolated hepatocytes has been used to assess the hepatotoxicity of certain chemicals because of animal welfare issues. However, whether an in vitro system can completely replace the in vivo system has yet to be elucidated in detail. Using a focused microarray established in our laboratory, we examined gene expression proiles in the mouse liver and primary cultured hepatocytes after treatment with different doses of acetaminophen, a widely used analgesic that frequently causes liver injury. The acute hepatotoxicity of acetaminophen was conirmed by showing the induction of an oxidative stress marker, heme oxygenase-1, elevated levels of serum transaminase, and histopathological indings. In vivo microarray and network analysis showed that acetaminophen treatment provoked alterations in relation to the inflammatory response, and that tumor necrosis factor-α plays a central role in related pathway alterations. By contrast, pathway analyses in in vitro isolated hepatocytes did not find such prominent changes in the inlammation-related networks compared with the in vivo situation. Thus, although in vitro gene expression proiles are useful for evaluating the direct toxicity of chemicals, indirect toxicities including inlammatory responses mediated by cell-cell interactions or secondary toxicity due to pathophysiological changes in the whole body may be overlooked. Our results indicate that the in vitro hepatotoxicity prediction system using isolated hepatocytes does not fully relect the in vivo cellular response. An in vitro system may be appropriate, therefore, for high throughput screening to detect the direct hepatotoxicity of a test compound.