Fatty acid oxidation in peripheral blood cells: Characterization and use for the diagnosis of defects of fatty acid oxidation

Abstract

Disorders of mitochondrial fatty acid oxidation are increasingly recognized as an important group of inborn errors of metabolism that are associated with a significant, but easily preventable, morbidity and mortality in children. However, diagnosis is often delayed because there is no easily applied method that detects all defects. Therefore, we have characterized the acylcarnitine intermediates of fatty acid oxidation in peripheral blood cells from healthy control volunteers and patients with four different defects. After selective permeabilization with historic II AS, a novel permeabilizing agent, the cells were incubated with [U-14C]hexadecanoate and β-oxidation flux and the acylcarnitine esters formed were measured. Blood cells from the control population produced large amounts of β-hydroxyacylcar-nitines and 2-enoylcarnitine esters, in addition to saturated acylcarnitine esters. This result is different from that found in other tissues (fibroblasts and muscle), where only saturated acylcarni Fatty acids are essential metabolic fuels in humans, especially at times of fasting or stress. They are predominantly oxidized in mitochondria by a series of repetitive enzymatic steps that generate acetyl-CoA and a chain-shortened fatty acyl-CoA ester until the acyl-CoA ester is completely cleaved into acetyl-CoA (1). In recent years a number of genetically distinct inborn errors of mitochondrial fatty acid oxidation have been described. These include abnormalities of short-chain acyl-coA dehydrogenase, MCAD, and VCLAD (1); ETF and ETF-oxidoreductase (2); trifunctional protein (3, 4); and CPTI and II (5). Inherited disorders of mitochondrial ß-oxida-tion are life threatening and relatively common diseases predominantly affecting infants and children. The clinical features include sudden infant death, hypoketotic hypoglycemic coma, Reye-like episodes, encephalopathy, myopathy, or cardiomytine esters could be detected. In blood cells from patients with defects of enzymes involved in long-chain fatty acid oxidation, flux was significantly reduced at 15 to 20% of control values (7.1 ± 2.3 nmol C2 units formed per minute per International Unit of citrate synthase activity). There was a characteristic accumulation of acylcarnitines that was pathognomonic for the site of the defect. Thus, analysis of β-oxidation intermediates from blood cells allows unequivocal identification of the four most common β-oxidation defects. © 1994 International Pediatric Research Foundation, Inc.