Mallory Bodies in Hepatocytes of Alcoholic Liver Disease and Primary Biliary Cirrhosis Contain Nε-(Carboxymethyl)lysine-Modified Cytokeratin, but not those in Hepatic Carcinoma Cells

Mallory bodies (MBs) are intracytoplasmic bodies seen in hepatocytes of alcoholic liver disease, primary biliary cirrhosis and hepatocellular carcinoma. However, the mechanism of MB formation has not been fully understood. Proteins could be modified to advanced glycation end products (AGEs) after long-term incubation with reducing sugar. AGEs are known to accumulate in several tissues in aging and age-enhanced disorders. To study the possible glycation process in the formation of MBs, hepatocytes of 80 human liver tissues with MBs were subjected to immunohistochemical analyses with five AGEs, two markers for oxidative stress proteins (OSPs) and four stress-response proteins (SRPs). MBs in hepatocytes of primary biliary cirrhosis and alcoholic liver disease were strongly positive for Nε-(carboxymethyl)lysine (CML) and weakly positive for pyrraline. MBs in hepatocellular carcinomas were negative for both CML and pyrraline. No significant immunoreactivity was detected in MBs for other AGEs, such as Nε-(carboxyethyl)lysine, pentosidine, and 3DG-imidazolone, or for OSPs and SRPs. Stainings for cytokeratin, a major protein component of MBs, and CML were co-localized. Furthermore, immunoblot analysis suggested that cytokeratin of MBs was modified to AGE, since a single protein band detected by a monoclonal anti-CML had a molecular weight identical to cytokeratin. The absence of the CML signal in MBs of hepatocellular carcinoma cells could be explained by scarce content of cytokeratin in carcinoma MBs.