A liver nuclear ethanol metabolizing system. Formation of metabolites that bind covalently to macromolecules and...

Recent studies from the laboratory reported the presence in highly purified liver nuclear preparations free of endoplasmic reticulum, mitochondria or cytosol, of an ethanol metabolizing group of enzymes (NEMS) leading to acetaldehyde and to hydroxyl and 1-hydroxyethyl (1HEt) free radicals. In the present study it is reported that when NEMS metabolize [14C]ethanol using NADPH as cofactor, its reactive metabolites bind covalently to nuclear proteins and lipids. No covalent binding to DNA was detected with presently used procedures. The covalent binding to nuclear proteins was acid labile and is mostly attributable to acetaldehyde. Additional evidence was attempted through studies where the acetaldehyde was identified as its 2,4-dinitrophenylhydrazone or as its pentafluorphenylhydrazone and gas chromatography (GC) analysis using electron capture detection. Values obtained were close to detection limit and of variable nature. The covalent binding to nuclear lipids involved phospholipids, fatty acids and esters and cholesterol free and esterified and it was only partially labile to acid treatment. Production of ethanol reactive metabolites such as acetaldehyde and free radicals, nearby liver nuclear DNA and nuclear proteins or lipids, might have significant toxicological consequences.