ALCOHOLIC LIVER INJURY: COVALENT BINDING OF ACETALDEHYD

Our previous studies have suggested that the covalent binding of
acetaldehyde to proteins may be responsible for the
hepatotoxicity of ethanol. These proposed studies will continue to
explore this possibility and, in this regard, the following
hypothesis has been formulated: During ethanol oxidation in the
liver, acetaldehyde forms stable adducts via binding to "reactive"
lysine residues of preferential target proteins; and such binding
results in impaired function of these proteins, leading eventually
to liver cell injury. The initial objective is to clarify the
chemistry of stable binding of acetaldehyde to proteins. By using
a previously developed HPLC technique, we intend to establish
the identities of the modified amino acid (lysine) residues
responsible for stable binding and to determine their structures.
In addition, we intend to establish the identity of the major
acetaldehyde-lysine adduct(s) formed in the liver during ethanol
oxidation and develop a reliable assay for detecting this adduct(s).
A second aim will utilize a hepatocyte culture model to study
adduct formation and degradation over extended time periods in
order to obtain information concerning the turnover of adducts in
the liver. Using this model, we will also initiate studies,
correlating the presence of adducts with cell viability and
hepatocyte function. As an initial attempt to establish a role of
stable adducts in liver injury, a third aim will investigate whether
differences exist in adduct formation and/or turnover in
periportal versus perivenous hepatocytes since the latter are more
susceptible to ethanol-induced injury. A fourth objective will be
to study the effects of stable acetaldehyde binding on the
function of actin and microsomal drug metabolism since both of
these models contain essential and reactive lysine residues. These
two systems could be potential targets of acetaldehyde binding in
the liver, and by accomplishing detailed studies with these two
specific systems, we hope to provide the rationale to look for
other key targets of binding. Finally, we hope to confirm the
presence of stable acetaldehyde-protein adducts in the liver (or
other organs) of chronically ethanol-fed rats, and to firmly
establish the identity of the "in vivo" lysine-acetaldehyde adduct.
Correlations between evidence of liver injury and the presence of
adducts will also be attempted in this model. These proposed
studies hopefully will give valuable information concerning the
basic molecular mechanisms of alcohol-induced hepatotoxicity.