Comparison of the formation of proteins modified by direct and indirect ethanol metabolites in the liver and blood of rats fed the Lieber-DeCarli liquid diet.
It has been proposed that proteins modified by ethanol metabolites, such as acetaldehyde (AcH) or alpha-hydroxyethyl radicals (HER) may be an important step in the aetiology of alcoholic liver disease. Furthermore, it has also been suggested that these modified proteins may act as a marker of ethanol intake. In this study, we have measured the generation of various types of modified proteins in the liver and blood of ethanol-fed rats. Multiple types of protein modification were observed in the livers of the ethanol-fed rats. In each case, the level of modification increased over the first 6 weeks of ethanol feeding, but reached a plateau by 10 weeks. In contrast to the liver, elevated levels of proteins modified by malondialdehyde were not seen in the plasma of ethanol-fed animals, whereas elevated levels of modification due to AcH and HER were observed. In haemolysates from these animals, only modification due to AcH was seen. Further investigation of the modification of plasma proteins showed that albumin, a protein produced in the liver, carried all the types of modification investigated, whereas immunoglobulin G, a protein derived from an extra-hepatic source, only carried modifications due to acetaldehyde. This study demonstrates for the first time that modification of plasma proteins by ethanol metabolites can occur at both intra- and extra-hepatic sites.