Inhibition of palmitate oxidation in mitochondria by lipid hydroperoxides

Linoleate monohydroperoxide (L-HPO), methyl linoleate monohydroperoxide (ML-HPO), and methyl hydroperoxy-epoxy-octadecenoate (ML-X) inhibited state 3 respiration of mitochondria when palmitate, palmitoyl CoA, or L-palmitoylcarnitine was used as a substrate. L-HPO was the most effective, and 50% inhibition of palmitate-supported respiration was observed with 2, 3.3, and 6.5 nmol/mg protein of L-HPO, ML-X, and ML-HPO, respectively. Almost the same values were obtained when palmitoyl CoA or L-palmitoylcarnitine was used in place of palmitate. L-HPO inhibited the reaction of beta-oxidation in mitochondria in a similar concentration range (4 nmol/mg protein for 50% inhibition) when L-palmitoylcarnitine was used as a substrate. L-HPO also inhibited the formation of 3-hydroxypalmitoylcarnitine from the same substrate. Carnitine palmitoyltransferase activity of mitochondria was inhibited by L-HPO, 50% inhibition occurring at 12 nmol/mg protein. These inhibitory effects of L-HPO were weaker when ATP was removed by hexokinase and glucose. ATP-dependent formation of carnitine ester of L-HPO was also suggested. It was deduced that L-HPO (and ML-X and ML-HPO after hydrolysis) was converted to carnitine ester and inhibited the palmitate metabolism at the site(s) of intramitochondrial carnitine palmitoyltransferase (and possibly acyl CoA dehydrogenase).