Effects of Reduced Phenolic Acids on Metabolism of Propionate and Palmitate in Bovine Liver Tissue In Vitro

Benzoic acid, 3-phenylpropionic acid, trans-cinnamic acid, and 3-(4-hydroxyphenyl)propionic acid in ruminal fluid are presumed to be the products of chemical reduction of dietary phenolic monomers by ruminal microorganisms. Effects of reduced phenolics on metabolism in bovine liver tissue were evaluated by measurement of 1) conversion of propionate to glucose and CO2, 2) conversion of palmitate to oxidized products, and 3) leakage of lactate dehydrogenase from liver slices in vitro. In Experiment 1, .4 mM benzoic, 3-phenylpropionic, trans-cinnamic, or 3-(4-hydroxyphenyl)propionic acids decreased conversion of propionate to glucose and decreased conversion of palmitate to total oxidation products. At .2 mM, 3-(4-hydroxyphenyl)propionic acid did not inhibit conversion of propionate to glucose compared with that of controls, but the other reduced phenolics did. In Experiment 2, the same reduced phenolics inhibited conversion of propionate to glucose. Of the reduced phenolics tested, cinnamic acid inhibited conversion of propionate to glucose at the lowest concentration, .1 mM. Additionally, when present at > or = .4, .1, or .005 mM, benzoic, 3-phenylpropionic, or trans-cinnamic acids, respectively, increased leakage of lactate dehydrogenase from liver tissue. The reduced phenolics tested, which are representative of those in ruminal fluid, inhibited metabolism of bovine liver tissue in vitro at supraphysiological concentrations. Data at physiological concentrations were inconclusive.