Quantitative measurement of total and free 3-hydroxy fatty acids in serum or plasma samples: short-chain 3-hydroxy fatty acids are not esterified.

摘要

Diagnostic protocols for disorders of mitochondrial fatty acid oxidation (FAO) generally include the measurement of plasma acylcarnitines. Many biochemical intermediates of FAO resulting from a metabolic block require carnitine conjugation for transport out of the mitochondria, and so occur as fatty acid carnitine conjugates in the blood. Both short- and long-chain acylcarnitines are generally determined, and this procedure has a critical role to play in the diagnosis of disorders of the very long-chain, medium-chain and short-chain acyl-CoA dehydrogenase defects. Less is known about the utility of acylcarnitines for the measurement of the various chain length intermediates of the 3-hydroxyacyl-CoA dehydrogenase steps of beta-oxidation. This study utilizes stable-isotope dilution gas chromatography-mass spectrometry to determine the serum or plasma concentrations of free 3-hydroxy fatty acids (3-OHFAs) of chain lengths C6 to C16. The 3-OHFA concentrations are determined in samples from normal individuals, hyperketotic individuals and patients with long-chain L-3-hydroxyacyl-CoA dehydrogenase and short-chain L-3-hydroxyacyl-CoA dehydrogenase deficiencies, both before and after hydrolysis. The results of the study indicate the relative amounts of conjugated intermediates of all chain lengths. Long-chain 3-OHFAs (C14 and C16) are found in elevated concentrations after hydrolysis, whereas short-chain and medium-chain 3-OHFAs (C6 to C12) show no difference in concentrations between the two samples in all subjects tested, suggesting that only long-chain 3-hydroxy species form conjugates. This finding has important implications for the use of the acylcarnitine assay for the diagnosis of defects involving short-chain and medium-chain 3-hydroxy fatty acids.