Mitochondrial metabolism of 12- and 15-hydroxyeicosatetraenoic acids

We have previously demonstrated that peroxisomal-deficient human skin fibroblasts and mutant Chinese hamster ovary cells do not convert 12- and 15-hydroxyeicosatetraenoic acids (HETEs) to chain-shortened, polar metabolites, suggesting that peroxisomes are the intracellular location for beta-oxidation of these compounds. This implies that mitochondria do not beta-oxidize HETEs. To test this hypothesis we incubated highly purified rat liver mitochondria with [3H]12-(S)- and [3H]15-(S)-HETE in the presence of carnitine and an acylcoenzyme A-generating system. Extracts obtained from these incubations were analyzed for radiolabeled polar metabolites. Both HETEs were converted to apparent products of beta-oxidation, although the 12-HETE compound was a markedly better substrate. The presence of 50 microM 2-tetradecyloxirane carboxylate, a potent inhibitor of carnitine palmitoyl transferase, completely blocked 12- and 15-HETE conversion to these metabolites as did omission of carnitine from the medium. These data demonstrate carnitine-dependent beta-oxidation of HETEs in isolated mitochondria and suggest that mitochondria are competent to carry out this metabolic process in eukaryotic cells. Prevailing metabolic conditions in subcellular compartments may have precluded observation of mitochondrial activity in our earlier work with cultured cells. Alternatively, transport mechanisms may exist in the cell types studied that distribute 12-(S)- and 15-(S)-HETEs specifically to peroxisomes.