Rates of H2O2 generation from peroxisomal beta-oxidation are sufficient to account for fatty acid-stimulated ethanol metabolism in perfused rat liver.

Fatty acids generate H2O2 via peroxisomal beta-oxidation and increase ethanol metabolism markedly in a system that involves catalase-H2O2. The present studies were conducted to understand why fatty acid-stimulated ethanol metabolism occurs much faster than rates of H2O2 generation reported previously in perfused rat liver. A new method was developed to measure rates of H2O2 generation based on the fact that methanol is oxidized only by catalase in rat liver. Rates of H2O2 generation were estimated from the time necessary for the steady-state level of catalase-H2O2 measured spectrophotometrically (660-640 nm) through a lobe of the liver to return to basal values following the addition of a known quantity of methanol in a closed perfusion system containing 4% bovine serum albumin. Under these conditions, basal rates of H2O2 production and rates of 4-methylpyrazole-insensitive ethanol oxidation were in a similar range (10 to 20 mumol/g/hr). Rates of H2O2 generation were increased up to 80 mumol/g/hr by addition of laurate, palmitate or oleate (1 mM); half-maximal increases in rates were observed with 0.6 mM oleate. Hexanoate, a short-chain fatty acid, did not stimulate H2O2 production or ethanol uptake. In these studies, rates of H2O2 generation compared well with rates of fatty acid-stimulated ethanol uptake measured in the presence of 4-methylpyrazole, an inhibitor of alcohol dehydrogenase, with all fatty acids studied. It is concluded, therefore, that rates of H2O2 generation are sufficient to account for rates of fatty acid-stimulated ethanol metabolism via catalase-H2O2. In addition, these data indicate that catalase may contribute significantly to ethanol oxidation under physiological conditions in the presence of fatty acids.