Role of malondialdehyde-acetaldehyde adducts in liver injury

Malondialdehyde and acetaldehyde react together with proteins in a synergistic manner and form hybrid protein adducts, designated as MAA adducts. MAA-protein adducts are composed of two major products whose structures and mechanism of formation have been elucidated. MAA adduct formation, especially in the liver, has been demonstrated in vivo during ethanol consumption. These protein adducts are capable of inducing a potent immune response, resulting in the generation of antibodies against both MAA epitopes, as well as against epitopes on the carrier protein. Chronic ethanol administration to rats results in significant circulating antibody titers against MAA-adducted proteins, and high anti-MAA titers have been associated with the severity of liver damage in humans with alcoholic liver disease. In vitro exposure of liver endothelial or hepatic stellate cells to MAA adducts induces a proinflammatory and profibrogenic response in these cells. Thus, during excessive ethanol consumption, ethanol oxidation and ethanol-induced oxidative stress result in the formation of acetaldehyde and malondialdehyde, respectively. These aldehydes can react together synergistically with proteins and generate MAA adducts, which are very immunogenic and possess proinflammatory and profibrogenic properties. By virtue of these potentially toxic effects, MAA adducts may play an important role in the pathogenesis of alcoholic liver injury.