The mechanism of inhibition of beta-oxidation by aspirin metabolites in skin fibroblasts from Reye's syndrome patients and controls

The effects of aspirin metabolites on beta-oxidation were studied in skin f ibroblasts from eight typical Reye's syndrome (RS) patients and controls. R S patients' cells did not differ from controls in rates of palmitate oxidat ion or in the three component activities of the mitochondrial trifunctional enzyme (MTE), indicating no inherited beta-oxidation defect. Aspirin metab olites salicylate, hydroxyhippurate and gentisate, but not aspirin, directl y inhibited palmitate oxidation in control and RS cells. RS cells were sign ificantly more sensitive to inhibition than controls at 0.5 to 5 mM salicyl ate. Inhibition was concentration-dependent and reversible. Inhibition did not occur in fibroblasts lacking activity of the long-chain 3-hydroxyacyl-C oA dehydrogenase (LCHAD) activity of MTE. Salicylate was therefore inhibiti ng beta-oxidation at this step. Hydroxyhippurate and salicylate reversibly inhibited HAD activities in extracts of control and RS cells. Studies with pure short-chain HAD and LCHAD (MTE) showed hydroxyhippurate and salicylate were competitive inhibitors of the former but mixed (not competitive) inhi bitors of the latter. Both compounds inhibited the combined, three-step, MT E reaction measured in the physiological direction. We conclude that (1) sa licylate and hydroxyhippurate decrease beta-oxidation in intact cells by re versible inhibition of LCHAD activity of the MTE, and (2) beta-oxidation in RS cells is inherently more sensitive to inhibition by low concentrations of salicylate than controls. (C) 1999 Elsevier Science B.V. All rights rese rved.