Role of reducing equivalents from fatty acid oxidation in mixed-function oxidation: studies with 2-bromooctanoate in the perfused rat liver.

Mixed-function oxidation of p-nitroanisole in isolated perfused livers from fasted rats was studied in the presence and absence of 2-bromooctanoate, an inhibitor of the beta-oxidation of acyl CoA compounds. These experiments were designed to test the hypothesis that reducing equivalents from fatty acid oxidation may play a role in drug metabolism in the fasted state. Complete inhibition of ketogenesis, as indicated by beta-hydroxybutyrate and acetoacetate production, was achieved with the addition of 0.6 mM 2-bromooctanoate to the perfusate. This concentration of 2-bromooctanoate had no effect on p-nitroanisole O-demethylation measured in isolated microsomes but diminished maximal rates of p-nitroanisole O-demethylation by 78% in perfused livers of fasted, phenobarbital-treated rats. No inhibition of p-nitroanisole O-demethylation was seen in perfused livers from fed rats. Intracellular concentrations of ATP, NADH, glutamate, alpha-ketoglutarate and isocitrate decreased significantly in the presence of 2-bromooctanoate; oxygen uptake also decreased by about 50%. These data indicate that by inhibiting endogenous acyl CoA oxidation, 2-bromooctanoate diminishes beta-oxidation of fatty acids, thereby decreasing the supply of NADH for the generation of ATP. This decreases the synthesis of NADPH, an obligatory cofactor for drug metabolism. 2-Bromooctanoate also decreased the concentration of intermediates which act through substrate shuttle mechanisms to move reducing equivalents from the mitochondrial into the extramitochondrial space. It is concluded that the decrease in mixed-function oxidation observed when beta-oxidation of fatty acids is inhibited with 2-bromooctanoate is due to diminished availability of mitochondrial reducing equivalents for the generation of cytosolic NADPH. 24CA-23080