Heat stress deteriorates mitochondrial β-oxidation of long-chain fatty acids in cultured fibroblasts with fatty acid β-oxidation disorders

Mitochondrial fatty acids β-oxidation disorder (FAOD) has become popular with development of tandem mass spectrometry (MS/MS) and enzymatic evaluation techniques. FAOD occasionally causes acute encephalopathy or even sudden death in children. On the other hand, hyperpyrexia may also trigger severe seizures or encephalopathy, which might be caused by the defects of fatty acid β-oxidation (FAO). We investigated the effect of heat stress on FAO to determine the relationship between serious febrile episodes and defect in β-oxidation of fatty acid in children. Fibroblasts from healthy control and children with various FAODs, were cultured in the medium loaded with unlabelled palmitic acid for 96 h at 37 °C or 41 °C. Acylcarnitine (AC) profiles in the medium were determined by MS/MS, and specific ratios of ACs were calculated. Under heat stress (at 41 °C), long-chain ACs (C12, C14, or C16) were increased, while medium-chain ACs (C6, C8, or C10) were decreased in cells with carnitine palmitoyl transferase II deficiency, very-long-chain acyl-CoA dehydrogenase deficiency and mitochondrial trifunctional protein deficiency, whereas AC species from short-chain (C4) to long-chain (C16) were barely affected in medium-chain acyl-CoA dehydrogenase and control. While long-chain ACs (C12–C16) were significantly elevated, short to medium-chain ACs (C4–C10) were reduced in multiple acyl-CoA dehydrogenase deficiency. These data suggest that patients with long-chain FAODs may be more susceptible to heat stress compared to medium-chain FAOD or healthy control and that serious febrile episodes may deteriorate long-chain FAO in patients with long-chain FAODs.     

A method for quantitative acylcarnitine profiling in human skin fibroblasts using unlabelled palmitic acid: diagnosis of fatty acid oxidation disorders and differentiation between biochemical phenotypes of MCAD deficiency

Inherited disorders of fatty acid oxidation are a group of acute life-threatening but treatable disorders, clinically complicated by severe hypoketotic hypoglycemia precipitated by prolonged fasting. Among them, medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is by far the most frequent disorder. Here we report a modified method for quantitative acylcarnitine profiling by electrospray ionisation-tandem mass spectrometry (ESI-MS-MS) in human skin fibroblasts using unlabelled palmitic acid as substrate. The reliability of this method was tested in cultured skin fibroblasts from previously diagnosed patients with specific carnitine cycle and fatty acid beta-oxidation defects. Furthermore, acylcarnitine profiling was investigated in fibroblasts and dried blood spots from patients with different variants of MCAD deficiency. ESI-MS-MS-based investigation of cultured skin fibroblasts from patients with disorders of fatty acid oxidation revealed a pathognomonic acylcarnitine profiling. In addition, this method delineated different variants of MCAD deficiency, i.e. mild and classical. The octanoylcarnitine (C8)-to-decanoylcarnitine (C10) and C8-to-acetylcarnitine (C2) ratios were the most specific markers to differentiate mild and classical forms of MCAD deficiency in fibroblasts. Similar results were obtained by quantitative acylcarnitine profiling in dried blood spots. In conclusion, this novel technique is a powerful tool for the investigation of fatty acid oxidation disorders under standardized conditions in fibroblasts.     

Quantitation of acyl-CoA and acylcarnitine esters accumulated during abnormal mitochondrial fatty acid oxidation.

We have used radio-high pressure liquid chromatography to study the acyl-CoA ester intermediates and the acylcarnitines formed during mitochondrial fatty acid oxidation. During oxidation of [U-14C]hexadecanoate by normal human fibroblast mitochondria, only the saturated acyl-CoA and acylcarnitine esters can be detected, supporting the concept that the acyl-CoA dehydrogenase step is rate-limiting in mitochondrial beta-oxidation. Incubations of fibroblast mitochondria from patients with defects of beta-oxidation show an entirely different profile of intermediates. Mitochondria from patients with defects in electron transfer flavoprotein and electron transfer flavoprotein:ubiquinone oxido-reductase are associated with slow flux through beta-oxidation and accumulation of long chain acyl-CoA and acylcarnitine esters. Increased amounts of saturated medium chain acyl-CoA and acylcarnitine esters are detected in the incubations of mitochondria with medium chain acyl-CoA dehydrogenase deficiency, whereas long chain 3-hydroxyacyl-CoA dehydrogenase deficiency is associated with accumulation of long chain 3-hydroxyacyl- and 2-enoyl-CoA and carnitine esters. These studies show that the control strength at the site of the defective enzyme has increased. Radio-high pressure liquid chromatography analysis of intermediates of mitochondrial fatty acid oxidation is an important new technique to study the control, organization and defects of the enzymes of beta-oxidation.     

Corresponding increase in long-chain acyl-CoA and acylcarnitine after exercise in muscle from VLCAD mice

Long-chain acylcarnitines accumulate in long-chain fatty acid oxidation defects, especially during periods of increased energy demand from fat. To test whether this increase in long-chain acylcarnitines in very long-chain acyl-CoA dehydrogenase (VLCAD(-/-)) knock-out mice correlates with acyl-CoA content, we subjected wild-type (WT) and VLCAD(-/-) mice to forced treadmill running and analyzed muscle long-chain acyl-CoA and acylcarnitine with tandem mass spectrometry (MS/MS) in the same tissues. After exercise, long-chain acyl-CoA displayed a significant increase in muscle from VLCAD(-/-) mice [C16:0-CoA, C18:2-CoA and C18:1-CoA in sedentary VLCAD(-/-): 5.95 +/- 0.33, 4.48 +/- 0.51, and 7.70 +/- 0.30 nmol x g(-1) wet weight, respectively; in exercised VLCAD(-/-): 8.71 +/- 0.42, 9.03 +/- 0.93, and 14.82 +/- 1.20 nmol x g(-1) wet weight, respectively (P < 0.05)]. Increase in acyl-CoA in VLCAD-deficient muscle was paralleled by a significant increase in the corresponding chain length acylcarnitine. Exercise resulted in significant lowering of the free carnitine pool in VLCAD(-/-) muscle. This is the first study demonstrating that acylcarnitines and acyl-CoA directly correlate and concomitantly increase after exercise in VLCAD-deficient muscle.     

Fluorometric assay of acyl-CoA dehydrogenases in normal and mutant human fibroblasts

A fluorimetric, ETF-linked procedure to determine activities of acyl-CoA dehydrogenase in cultured human fibroblasts is described. The assay readily distinguishes between cell lines deficient in medium-chain acyl-CoA dehydrogenase, long-chain acyl-CoA dehydrogenase, isovaleryl-CoA dehydrogenase, and controls, and may allow for the diagnosis of heterozygous carriers of these disorders. The method has been made feasible with the development of rapid and efficient procedures to isolate ETF, and offers several advantages over procedures that are currently employed.     

Characterization of mitochondrial proteome in a severe case of ETF-QO deficiency

Multiple acyl-CoA dehydrogenase deficiency (MADD) is a mitochondrial fatty acid oxidation disorder caused by mutations that affect electron transfer flavoprotein (ETF) or ETF:ubiquinone oxidoreductase (ETF-QO) or even due to unidentified disturbances of riboflavin metabolism. Besides all the available data on the molecular basis of FAO disorders, including MADD, the pathophysiological mechanisms underlying clinical phenotype development, namely at the mitochondrial level, are poorly understood. In order to contribute to the elucidation of these mechanisms, we isolated mitochondria from cultured fibroblasts, from a patient with a severe MADD presentation due to ETF-QO deficiency, characterize its mitochondrial proteome and compare it with normal controls. The used approach (2-DE-MS/MS) allowed the positive identification of 287 proteins in both patient and controls, presenting 35 of the significant differences in their relative abundance. Among the differentially expressed are proteins associated to binding/folding functions, mitochondrial antioxidant enzymes as well as proteins associated to apoptotic events. The overexpression of chaperones like Hsp60 or mitochondrial Grp75, antioxidant enzymes and apoptotic proteins reflects the mitochondrial response to a complete absence of ETF-QO. Our study provides a global perspective of the mitochondrial proteome plasticity in a severe case of MADD and highlights the main molecular pathways involved in its pathogenesis.     

Mutations at the flavin binding site of ETF:QO yield a MADD-like severe phenotype in Drosophila

Following a screening on EMS-induced Drosophila mutants defective for formation and morphogenesis of epithelial cells, we have identified three lethal mutants defective for the production of embryonic cuticle. The mutants are allelic to the CG12140 gene, the fly homologue of electron transfer flavoprotein:ubiquinone oxidoreductase (ETF:QO). In humans, inherited defects in this inner membrane protein account for multiple acyl-CoA dehydrogenase deficiency (MADD), a metabolic disease of β-oxidation, with a broad range of clinical phenotypes, varying from embryonic lethal to mild forms. The three mutant alleles carried distinct missense mutations in ETF:QO (G65E, A68V and S104F) and maternal mutant embryos for ETF:QO showed lethal morphogenetic defects and a significant induction of apoptosis following germ-band elongation. This phenotype is accompanied by an embryonic accumulation of short- and medium-chain acylcarnitines (C4, C8 and C12) as well as long-chain acylcarnitines (C14 and C16:1), whose elevation is also found in severe MADD forms in humans under intense metabolic decompensation. In agreement the ETF:QO activity in the mutant embryos is markedly decreased in relation to wild type activity. Amino acid sequence analysis and structural mapping into a molecular model of ETF:QO show that all mutations map at FAD interacting residues, two of which at the nucleotide-binding Rossmann fold. This structural domain is composed by a β-strand connected by a short loop to an α-helix, and its perturbation results in impaired cofactor association via structural destabilisation and consequently enzymatic inactivation. This work thus pinpoints the molecular origins of a severe MADD-like phenotype in the fruit fly and establishes the proof of concept concerning the suitability of this organism as a potential model organism for MADD.     

Beta-oxidation of long-chain fatty acids by human fibroblasts: evidence for a novel long-chain acyl-coenzyme A dehydrogenase.

Fibroblasts from patients with long-chain acyl-CoA dehydrogenase deficiency were found to oxidize [1-14C]linoleate at an average rate of 60% of normal but [9,10(n)-3H]myristate at an average rate of only 37% of normal, a relationship reverse from that predicted by the chain-length specificities of the three known straight-chain mitochondrial acyl-CoA dehydrogenases. The residual long-chain beta-oxidative activity was found to be mitochondrial and associated with the accumulation of tetradecadienoate (C14:2w6) when the mutant fibroblasts were incubated with 100 mumol/L linoleate (C18:2w6) or eicosadienoate (C20:2w6). The results suggest the presence in human fibroblasts of a novel acyl-CoA dehydrogenase with activity toward 15 to 20 carbon-length fatty acids.     

Electron-transferring flavoprotein from pig kidney: flavin analogue studies

Apo-electron-transferring flavoprotein from pig kidney (apo-ETF) has been prepared by an acid ammonium sulfate procedure and reconstituted with FAD analogues to probe the flavin binding site. The 8-position of the bound flavin is accessible to solvent as judged by the reaction of 8-Cl-FAD-ETF with sodium sulfide and thiophenol. A series of 8-alkylmercapto-FAD analogues containing increasingly bulky substituents bind tightly to apo-ETF and can be reduced to the dihydroflavin level by octanoyl-CoA in the presence of catalytic levels of the medium-chain acyl-CoA dehydrogenase. Bulky substituents severely slow the rate of these interflavin electron-transfer reactions. In the case of the 8-cyclohexylmercapto derivative, this decrease reflects a sizable increase in the Km for ETF (approximately 14-fold) with only a 20% decrease in Vmax. Reduction of all of these 8-substituted derivatives involves the accumulation of ETF anion radical intermediates. Dihydro-5-deaza-FAD dehydrogenase, unlike the corresponding 1-deazaflavin substitution, is unable to reduce native ETF despite a strongly favorable redox potential difference. These results, together with data from the native proteins, are consistent with obligatory 1-electron transfer between dehydrogenase and ETF possibly involving the exposed dimethylbenzene edge of ETF. Irradiation of apo-ETF reconstituted with the photoaffinity analogue 8-azidoflavin leads to approximately 10% covalent incorporation of the flavin. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of apo-ETF labeled with tritiated 8-azido-FAD shows preferential labeling of the smaller subunit (88%, Mr 30,000 subunit; 12%, Mr 33,000 subunit).(ABSTRACT TRUNCATED AT 250 WORDS)     

Enzymatic diagnosis of medium-chain acyl-CoA dehydrogenase deficiency by detecting 2-octenoyl-CoA production using high-performance liquid chromatography: a practical confirmatory test for tandem mass spectrometry newborn screening in Japan

Many of the previously described enzymatic assay methods for the diagnosis of medium-chain acyl-CoA dehydrogenase (MCAD) deficiency have been dependent upon the measurement of radioisotope-labeled co-products or reduction of electron acceptors. We have developed a direct assay method to detect 2-enoyl-CoA production using high-performance liquid chromatography (HPLC). Crude cell lysate prepared from lymphocytes were incubated with n-octanoyl-CoA and ferrocenium hexafluorophosphate. The detection of 2-octenoyl-CoA was significantly reproducible. We applied the assay to samples from four infants suspected to have MCAD deficiency by tandem mass spectrometry (MS/MS) newborn screening conducted in the Hiroshima area of Japan. Three of them were proved to have pathologically reduced residual enzyme activities, although they were associated with various clinical and biochemical phenotypes. In addition, another symptomatic Japanese patient and her presymptomatic sibling who were detected by MS/MS selective screening were successfully diagnosed by our enzymatic assay. These results indicate that the method can be a useful confirmatory test for MS/MS screening of MCAD deficiency.     

Immunoprecipitation and electrophoretic analysis of four human acyl-CoA dehydrogenases and electron transfer flavoprotein using antibodies raised against the corresponding rat enzymes

We prepared monospecific antisera in rabbits against purified rat short-, medium-, and long-chain acyl-CoA dehydrogenases, isovaleryl-CoA dehydrogenase, and ETF and tested the immunocross-reactivity to the corresponding human enzymes. Each antiserum specifically reacted with the corresponding human enzyme. When immunoprecipitates were analyzed by SDS-PAGE, the mobilities of all the human acyl-CoA dehydrogenases and ETF subunits were identical to those of the rat counterparts with a single exception. Human medium-chain acyl-CoA dehydrogenase had a mobility on SDS-PAGE slightly slower than that of rat medium-chain acyl-CoA dehydrogenase, suggesting that human medium-chain acyl-CoA dehydrogenase was 1 kDa larger than the rat counterpart. The immunocross-reactivity of the antisera, raised against the rat acyl-CoA dehydrogenases and ETF to the human counterpart, provide useful tools for the study of mutant enzymes in cells from patients with a genetic defect of acyl-CoA dehydrogenases of ETF.     

Peroxisomes contribute to the acylcarnitine production when the carnitine shuttle is deficient

Fatty acid β-oxidation may occur in both mitochondria and peroxisomes. While peroxisomes oxidize specific carboxylic acids such as very long-chain fatty acids, branched-chain fatty acids, bile acids, and fatty dicarboxylic acids, mitochondria oxidize long-, medium-, and short-chain fatty acids. Oxidation of long-chain substrates requires the carnitine shuttle for mitochondrial access but medium-chain fatty acid oxidation is generally considered carnitine-independent. Using control and carnitine palmitoyltransferase 2 (CPT2)- and carnitine/acylcarnitine translocase (CACT)-deficient human fibroblasts, we investigated the oxidation of lauric acid (C12:0). Measurement of the acylcarnitine profile in the extracellular medium revealed significantly elevated levels of extracellular C10- and C12-carnitine in CPT2- and CACT-deficient fibroblasts. The accumulation of C12-carnitine indicates that lauric acid also uses the carnitine shuttle to access mitochondria. Moreover, the accumulation of extracellular C10-carnitine in CPT2- and CACT-deficient cells suggests an extramitochondrial pathway for the oxidation of lauric acid. Indeed, in the absence of peroxisomes C10-carnitine is not produced, proving that this intermediate is a product of peroxisomal β-oxidation. In conclusion, when the carnitine shuttle is impaired lauric acid is partly oxidized in peroxisomes. This peroxisomal oxidation could be a compensatory mechanism to metabolize straight medium- and long-chain fatty acids, especially in cases of mitochondrial fatty acid β-oxidation deficiency or overload.     

Online immunoaffinity liquid chromatography/tandem mass spectrometry determination of a type II collagen peptide biomarker in rat urine: Investigation of the impact of collision-induced dissociation fluctuation on peptide quantitation

Proteolytic fragments of type II collagen, a major component of joint tissue, have recently been identified as biomarkers for osteoarthritis, a progressive disease associated with cartilage degeneration. A liquid chromatography/tandem mass spectrometry (MS/MS) assay that utilizes online immunoaffinity chromatography and column switching was developed in our laboratory for the neoepitope of type II collagen (NET2C). During method development, peptide collision-induced dissociation (CID) was found to be a significant source of assay variation, which exceeded 10% CV, despite the fact that a stable-isotope-labeled (SIL) internal standard was used to minimize imprecision. This phenomenon was studied in detail using peptides and associated SIL internal standards of varying lengths and amino acid compositions. Variability in peptide CID necessitated the monitoring of multiple MS/MS transitions to obtain acceptable assay precision. The assay was subsequently validated to measure NET2C concentrations in rat urine over the range of 0.1 to 10 ng/mL. The interday accuracy and precision ranged from 3.9 to 13.1 (%CV) and 10.7 to 5.3 (%RE), respectively, across the range of validated concentrations. A specific application of the assay is presented in which the role of estrogen deficiency in the development and progression of osteoarthritis was investigated. In this study, the effect of estrogen on lowering NET2C concentrations in urine in ovariectomized rats was demonstrated.     

Carnitine metabolism in the vitamin B-12-deficient rat.

In vitamin B-12 (cobalamin) deficiency the metabolism of propionyl-CoA and methylmalonyl-CoA are inhibited secondarily to decreased L-methylmalonyl-CoA mutase activity. Production of acylcarnitines provides a mechanism for removing acyl groups and liberating CoA under conditions of impaired acyl-CoA utilization. Carnitine metabolism was studied in the vitamin B-12-deficient rat to define the relationship between alterations in acylcarnitine generation and the development of methylmalonic aciduria. Urinary excretion of methylmalonic acid was increased 200-fold in vitamin B-12-deficient rats as compared with controls. Urinary acylcarnitine excretion was increased in the vitamin B-12-deficient animals by 70%. This increase in urinary acylcarnitine excretion correlated with the degree of metabolic impairment as measured by the urinary methylmalonic acid elimination. Urinary propionylcarnitine excretion averaged 11 nmol/day in control rats and 120 nmol/day in the vitamin B-12-deficient group. The fraction of total carnitine present as short-chain acylcarnitines in the plasma and liver of vitamin B-12-deficient rats was increased as compared with controls. When the rats were fasted for 48 h, relative or absolute increases were seen in the urine, plasma, liver and skeletal-muscle acylcarnitine content of the vitamin B-12-deficient rats as compared with controls. Thus vitamin B-12 deficiency was associated with a redistribution of carnitine towards acylcarnitines. Propionylcarnitine was a significant constituent of the acylcarnitine pool in the vitamin B-12-deficient animals. The changes in carnitine metabolism were consistent with the changes in CoA metabolism known to occur with vitamin B-12 deficiency. The vitamin B-12-deficient rat provides a model system for studying carnitine metabolism in the methylmalonic acidurias.     

Stabilization of non-productive conformations underpins rapid electron transfer to electron-transferring flavoprotein

Crystal structures of protein complexes with electron-transferring flavoprotein (ETF) have revealed a dual protein-protein interface with one region serving as anchor while the ETF FAD domain samples available space within the complex. We show that mutation of the conserved Glu-165beta in human ETF leads to drastically modulated rates of interprotein electron transfer with both medium chain acyl-CoA dehydrogenase and dimethylglycine dehydrogenase. The crystal structure of free E165betaA ETF is essentially identical to that of wild-type ETF, but the crystal structure of the E165betaA ETF.medium chain acyl-CoA dehydrogenase complex reveals clear electron density for the FAD domain in a position optimal for fast interprotein electron transfer. Based on our observations, we present a dynamic multistate model for conformational sampling that for the wild-type ETF. medium chain acyl-CoA dehydrogenase complex involves random motion between three distinct positions for the ETF FAD domain. ETF Glu-165beta plays a key role in stabilizing positions incompatible with fast interprotein electron transfer, thus ensuring high rates of complex dissociation.     

An accurate and sensitive assay of [14C]octanoate oxidation and its application on tissue homogenates and fibroblasts

A procedure was developed to assay [14C]octanoate oxidation from the production of both 14CO2 and 14C-labeled acid-soluble products. Octanoic acid and its CoA and carnitine esters were eliminated from the acid-soluble products by alkaline hydrolysis of the esters and acidification and binding of the acid to Lipidex 1000. The method was evaluated with homogenates of various rat tissues and human muscles and with human fibroblasts. 14CO2 production was variable and comprised less than 3% of the total oxidation products with homogenates and 26 +/- 19% with fibroblasts. As compared to palmitate, oxidation rates of octanoate were higher in rat liver and heart homogenates, of the same magnitude in muscle homogenates, but lower in fibroblasts. The proportion of antimycin-insensitive oxidation was much lower with octanoate than with palmitate. Using the assay a case of medium-chain acyl-CoA dehydrogenase deficiency could be indicated.     

A new,simple assay for long-chain acyl-CoA dehydrogenase in cultured skin fibroblasts using stable isotopes and GC-MS

In this paper, we present a new method for measurement of long-chain acyl-CoA dehydrogenase (LCAD) activities in cultured skin fibroblasts. The method is based upon gas chromatographic/mass spectrometric determination of 3-OH-hexadecanoic acid formed during incubation of fibroblasts in a medium containing palmitoyl-CoA and crotonase, to convert the enoyl-CoA ester produced into the 3-hydroxyacyl-CoA ester. The validity of the method demonstrated by the finding of a full deficiency of LCAD in fibroblasts from three patients with an established deficiency of LCAD.     

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency: diagnosis by acylcarnitine analysis in blood.

Medium-chain acyl-coenzyme A dehydrogenase (MCAD) deficiency is a disorder of fatty acid catabolism, with autosomal recessive inheritance. The disease is characterized by episodic illness associated with potentially fatal hypoglycemia and has a relatively high frequency. A rapid and reliable method for the diagnosis of MCAD deficiency is highly desirable. Analysis of specific acylcarnitines was performed by isotope-dilution tandem mass spectrometry on plasma or whole blood samples from 62 patients with MCAD deficiency. Acylcarnitines were also analyzed in 42 unaffected relatives of patients with MCAD deficiency and in other groups of patients having elevated plasma C8 acylcarnitine, consisting of 32 receiving valproic acid, 9 receiving medium-chain triglyceride supplement, 4 having multiple acyl-coenzyme A dehydrogenase deficiency, and 8 others with various etiologies. Criteria for the unequivocal diagnosis of MCAD deficiency by acylcarnitine analysis are an elevated C8-acylcarnitine concentration (> 0.3 microM), a ratio of C8/C10 acylcarnitines of > 5, and lack of elevated species of chain length > C10. These criteria were not influenced by clinical state, carnitine treatment, or underlying genetic mutation, and no false-positive or false-negative results were obtained. The same criteria were also successfully applied to profiles from neonatal blood spots retrieved from the original Guthrie cards of eight patients. Diagnosis of MCAD deficiency can therefore be made reliably through the analysis of acylcarnitines in blood, including presymptomatic neonatal recognition. Tandem mass spectrometry is a convenient method for fast and accurate determination of all relevant acylcarnitine species.     

Strategies for Correcting Very Long Chain Acyl-CoA Dehydrogenase Deficiency

Very long acyl-CoA dehydrogenase (VLCAD) deficiency is a genetic pediatric disorder presenting with a spectrum of phenotypes that remains for the most part untreatable. Here, we present a novel strategy for the correction of VLCAD deficiency by increasing mutant VLCAD enzymatic activity. Treatment of VLCAD-deficient fibroblasts, which express distinct mutant VLCAD protein and exhibit deficient fatty acid β-oxidation, with S-nitroso-N-acetylcysteine induced site-specific S-nitrosylation of VLCAD mutants at cysteine residue 237. Cysteine 237 S-nitrosylation was associated with an 8–17-fold increase in VLCAD-specific activity and concomitant correction of acylcarnitine profile and β-oxidation capacity, two hallmarks of the disorder. Overall, this study provides biochemical evidence for a potential therapeutic modality to correct β-oxidation deficiencies.     

A new, simple assay for long-chain acyl-CoA dehydrogenase in cultured skin fibroblasts using stable isotopes and GC-MS.

In this paper, we present a new method for measurement of long-chain acyl-CoA dehydrogenase (LCAD) activities in cultured skin fibroblasts. The method is based upon gas chromatographic/mass spectrometric determination of 3-OH-hexadecanoic acid formed during incubation of fibroblasts in a medium containing palmitoyl-CoA and crotonase, to convert the enoyl-CoA ester produced into the 3-hydroxyacyl-CoA ester. The validity of the method is demonstrated by the finding of a full deficiency of LCAD in fibroblasts from three patients with an established deficiency of LCAD.