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Succinic semialdehyde dehydrogenase deficiency, a rare inherited defect of gamma-aminobutyrate (GABA) catabolism, presents with characteristic biochemical abnormalities in the central nervous system (CNS). These include elevated concentrations of GABA, gamma-hydroxybutyrate (GHB), succinic semialdehyde (SSA), 4,5-dihydroxyhexanoic acid (DHHA) and alanine as well as decreased concentrations of glutamine. GABA degradation is coupled to Krebs cycle function in mammalian CNS ("GABA shunt") through succinate and alpha-ketoglutarate. Accordingly, we hypothesized that disruption of Krebs cycle and respiratory chain function in the CNS is involved in the neuropathogenesis of this disease. For this purpose, we investigated cerebral activities of Krebs cycle and respiratory chain enzymes as well as the glutathione content in Aldh5a1(-/-) mice, a recently generated mouse model for this disease. In CNS tissue of Aldh5a1(-/-) mice, we found a significantly decreased glutathione content (hippocampus, cortex) and decreased activities of complexes I-IV (hippocampus) suggesting increased oxidative stress and mitochondrial dysfunction. However, specific activities of Krebs cycle and respiratory chain were not affected by GABA, GHB, SSA, or DHHA (up to 1 mmol/L). Although our results suggest hippocampal and cortical dysfunction in Aldh5a1(-/-) brain, we found no evidence that accumulating key metabolites of SSADH deficiency directly induce impairment of energy metabolism.

We investigated the presence of hydroxyacid-oxoacid transhydrogenase (HOT), which catalyses the cofactor-independent conversion of gamma-hydroxybutyrate (GHB) to succinic semialdehyde coupled to reduction of 2-ketoglutarate (2-KG) to D-2-hydroxyglutarate (D-2-HG), in human liver extracts employing [2H6]GHB and 2-KG as substrates. We measured incorporation of 2H in D-[2H]2-HG using GC-MS analyses, providing evidence for HOT activity in humans. Kinetic characterization of HOT was undertaken in forward and reverse directions. We employed [2H6]GHB and [2H4]2-KG as cosubstrates in order to develop a HOT activity assay in cultured human fibroblasts derived from patients with D-2-hydroxyglutaric aciduria. HOT activity was quantified in this system by the measurement of D-[2H5]2-HG production. Fibroblasts derived from patients with D-2-hydroxyglutaric aciduria showed normal HOT activities. Our results provide the first demonstration and preliminary kinetic characterization of HOT activity in human tissues.

This paper describes a stable isotope dilution method for quantification of 3-hydroxyglutaric acid (3-HGA) in body fluids. The method comprises a solid-phase extraction procedure, followed by gas chromatographic separation and negative chemical ionization mass spectrometric detection. This method is selective and sensitive, and enables measurement of 3-HGA concentrations in urine-, plasma-, and CSF- samples of controls. The control ranges for 3-HGA were: urine 0.88-4.5 mmol/mol creatinine (n=12); plasma 0.018-0.10 micro mol/l (n=10), CSF 0.022-0.067 micro mol/l (n=10). We applied this method to measure 3-HGA in body fluids of three patients with glutaric aciduria type I. We also quantified 3-HGA in amniotic fluid of controls (range 0.056-0.11 micro mol/l; n=12) and in two samples from fetuses affected with glutaric aciduria type I.

The mono-(dimethylaminoethyl) succinyl (MDMAES) ester is a new derivative for rapid, mild, and sensitive electrospray ionization tandem mass spectrometry (ESI-MS/MS) analysis of cholesterol and dehydrocholesterol. It is an order of magnitude more sensitive than the previous most practical alternative, the N-methylpyridyl ether derivative. The MDMAES derivative was used to develop a rapid screening procedure for the biochemical diagnosis of Smith-Lemli-Opitz syndrome (SLOS) by measuring the dehydrocholesterol/cholesterol ratio in plasma (5 microl) and plasma spotted onto filter paper. Details of the synthesis of [25,26,26,26,27,27,27-(2)H7]-7-dehydrocholesterol, used as a standard for quantitation, are included. The measurement of total sterols as MDMAES esters, after base hydrolysis of plasma, afforded a dehydrocholesterol/cholesterol ratio of 0.05-2.95 for SLOS patient samples (n = 5) compared with 0.001-0.003 for normal adult controls (n = 20). Direct hexane extraction of plasma without base hydrolysis enabled the measurement of free sterols with a total sample analysis time of

A subgroup of peroxisomal disorders, peroxi- some biogenesis defects (PBD), can be differentiated by el- evated levels of C 27 bile acids in plasma and bile. Patients with peroxisomal disorders, who lack the ability to chain- shorten the C 27 bile acid intermediates into C 24 bile acids, show elevated levels of C 27 bile acids, notably 3 a ,7 a -dihy- droxy-5 b -cholest-26-oic acid and 3 a ,7 a ,12 a -trihydroxy-5 b - cholestan-26-oic acid. C 27 bile acids are normally estimated against other bile acid standards, by time-consuming gas chromatography-mass spectrometry and liquid chromatog- raphy-tandem mass spectrometry methods, in plasma (mini- mum of 50 m l). In this article we describe the quantitation of unconjugated di- and trihydroxy C 27 bile acids in 5- m l plasma samples and 3-mm blood spots, using deuterium- labeled internal standards. The synthesis of 2 H 3 -labeled di- and trihydroxycoprostanic acids is described. The sample preparation and analysis by electrospray tandem mass spec- trometry (ES-MS/MS) takes less than 1 h and features di- methylaminoethyl ester derivatives. The levels of the di- and trihydroxy bile acids are significantly higher in PBD patients than in age-matched control subjects for both plasma and blood spots collected at birth (some stored for up to 18 years). Excellent correlation is observed between the C 26:0 /C 22:0 very long chain fatty acid (VLCFA) ratio and the levels of trihy- droxy C 27 bile acids in plasma from PBD patients. The ES-MS/MS method can be used to rapidly screen for PBD patients in plasma samples with elevated C 26:0 /C 22:0 VLCFA ratios and in archived collections of neonatal blood spots. —Johnson, D. W., H. J. ten Brink, R. C. Schuit, and C. Jakobs. Rapid and quantitive analysis of unconjugated C 27 bile acids in plasma and blood samples by tandem mass spectrometry. J. Lipid Res. 2001. 42: 9-16.

The analysis of acylglycines is an important biochemical tool for the diagnosis of inherited disorders of mitochondrial fatty acid P-oxidation. A stable isotope dilution gas chromatography negative chemical ionisation mass spectrometry method for the quantitative analysis of short and medium-chain acylglycines as their bis(trifluoromethyl)benzyl (BTFMB) ester derivatives is described. The diagnostic usefulness of the method was demonstrated in nine patients with medium-chain acyl-coenzyme A (CoA) dehydrogenase (MCAD) deficiency, and seven patients with multiple acyl-CoA dehydrogenation defect (MAD). The urinary acylglycine profiles in these patients were compared to those in controls (n = 19), children on a medium-chain triglyceride (MCT) supplemented diet (n = 4), and patients with various other diseases (n = 5). (C) 2000 Elsevier Science B.V. All rights reserved.

A previously described method for the determination of GABA in CSF has been expanded to include both GABA and beta-ALA, using a single GC-MS analysis. A stable isotope labelled internal standard for beta-ALA was synthesised to achieve accurate quantification. This new combined method expands the diagnostic power compared to an isolated GABA measurement. Control values for free and total GABA and free and total beta-ALA are described. Age2 years: free GABA 0.017-0.067 microM, total GABA 4.2-13.4 microM; free beta-ALA 0.049-0.11 microM, total beta-ALA 2.1-4.6 microM. Age2 years: free GABA 0.032-0.17 microM, total GABA 3.3-12.2 microM; free beta-ALA 0.021-0.058 microM, total beta-ALA 0.91-3.5 microM.

In this paper we report the development of highly sensitive, selective, and accurate stable isotope dilu- tion gas chromatography negative chemical ionization mass spectrometry (GC-NCI-MS) methods for quantification of peroxisomal b -oxidation intermediates of pristanic acid in human plasma: 2,3-pristenic acid, 3-hydroxypristanic acid, and 3-ketopristanic acid. The carboxylic groups of the inter- mediates were converted into pentafluorobenzyl esters, whereas hydroxyl groups were acetylated and ketogroups were methoximized. Hereafter, the samples were subjected to clean-up by high performance liquid chromatography. Analyses were performed by selected monitoring of the car- boxylate anions of the derivatives. Control values of all three metabolites were established (2,3-pristenic acid: 2-48 n m , 3-hydroxypristanic acid: 0.02-0.81 n m , 3-ketopristanic acid: 0.07-1.45 n m ). A correlation between the concentra- tions of pristanic acid and its intermediates in plasma was found. The diagnostic value of the methods is illustrated by measurements of the intermediates in plasma from patients with peroxisomal disorders. It is shown that in generalized peroxisomal disorders, the absolute concentrations of 2,3- pristenic acid, 3-hydroxypristanic acid, and 3-ketopristanic acid were comparable to those in the controls, whereas rela- tive to the pristanic acid concentrations these intermediates were significantly decreased. In bifunctional protein defi- ciency, elevated levels of 2,3-pristenic acid and 3-hydroxy- pristanic acid were found. 3-Ketopristanic acid, although within the normal range, was relatively low when compared to the high pristanic acid levels in these patients. —Ver- hoeven, N. M., D. S. M. Schor, E. A. Struys, E. E. W. Jan- sen, H. J. ten Brink, R. J. A. Wanders, and C. Jakobs. Analysis of pristanic acid b -oxidation intermediates in plasma from healthy controls and patients affected with peroxisomal dis- orders by stable isotope dilution gas chromatography mass spectrometry. J. Lipid Res. 1999. 40: 260-266.

A stable isotope dilution method was developed for the measurement of 2-hydroxyphytanic acid and 2-oxophytanic acid in plasma. In plasma from healthy individuals and from patients with Refsum's disease, 2-hydroxyphytanic acid was found at levels less than 0.2 mumol/l, whereas the acid accumulated in plasma from patients with rhizomelic chondrodysplasia punctata, generalized peroxisomal dysfunction, and a single peroxisomal beta-oxidation enzyme deficiency. In plasma from both healthy controls and patients with peroxisomal disorders, 2-oxophytanic acid was undetectable. Four different groups of diseases were characterized with a defective phytanic acid alpha-oxidation and/or pristanic acid beta-oxidation: 1) Refsum's disease, with a defect at phytanic acid alpha-hydroxylation; 2) rhizomelic chondrodysplasia punctata, with a defect at 2-hydroxyphytanic acid decarboxylation; 3) generalized peroxisomal disorders, with defects at 2-hydroxyphytanic acid decarboxylation and at pristanic acid beta-oxidation; 4) single peroxisomal beta-oxidation enzyme deficiencies, with a defect at pristanic acid beta-oxidation, resulting in an impaired phytanic acid alpha-oxidation by inhibition. The results indicate that 2-hydroxyphytanic acid decarboxylation and pristanic acid beta-oxidation take place in peroxisomes.

A sensitive and selective stable isotope dilution method was developed for the accurate quantitation of pristanic acid and phytanic acid using electron capture negative ion mass fragmentography on pentafluorobenzyl derivatives. This technique allows detection of 1 pg of each compound and was applied to plasma from healthy controls and patients suffering from various peroxisomal disorders. The age-dependency of phytanic and pristanic acid levels in plasma from healthy controls was demonstrated. The involvement of peroxisomes in the beta-oxidation of pristanic acid was concluded from its accumulation in plasma from patients with peroxisomal deficiencies. Pristanic acid/phytanic acid ratios were markedly increased in bifunctional protein and/or 3-oxoacyl-CoA thiolase deficiency, indicating their role in the (differential) diagnosis of disorders of peroxisomal beta-oxidation.

The novel and rapid assay presented here combines high-performance liquid chromatography and electrospray ionisation tandem mass spectrometry (HPLC-ESI-MS/MS) to directly measure and quantify the CoA esters of 3alpha,7alpha,12alpha-trihydroxy- and 3alpha,7alpha-dihydroxy-5beta-cholestan-26-oic acid (THCA and DHCA). The latter are converted inside peroxisomes to the primary bile acids, cholic and chenodeoxycholic acids, respectively. Prior to MS/MS, esters were separated by reversed-phase HPLC on a C(18) column using an isocratic mobile phase (acetonitrile/water/2-propanol) and subsequently detected by multiple reaction monitoring. For quantification, the CoA ester of deuterium-labelled 3alpha,7alpha,12alpha-trihydroxy-5beta-cholan-24-oic acid (d(4)-CA) was used as internal standard. To complete an assay took less than 8 min. To verify the validity of the assay, the effect of peroxisomal proteins on the efficacy of extraction of the CoA esters was tested. To this end, variable amounts of the CoA esters were spiked with a fixed amount of either intact peroxisomes or peroxisomal matrix proteins and then extracted using a solid-phase extraction system. The CoA esters could be reproducibly recovered in the range of 0.1-4 micromol l(-1) (linear correlation coefficient R(2) > 0.99), with a detection limit of 0.1 micromol l(-1). In summary, electrospray ionization tandem mass spectrometry combined with HPLC as described here proved to be a rapid and versatile technique for the determination of bile acid CoA esters in a mixture with peroxisomal proteins. This suggests this technique to become a valuable tool in studies dealing with the multi-step biosynthesis of bile acids and its disturbances in disorders like the Zellweger syndrome.

Concentrations of phytanic acid and pristanic acid were measured in stored dried blood spots collected at neonatal screening from patients with peroxisomal disorders, and compared with concentrations in control blood spots. In blood spots from two patients with Zellweger syndrome both phytanic acid and pristanic acid concentrations were increased but their concentration ratio was normal. In the blood spot from a patient with rhizomelic chondrodysplasia punctata, the concentration of phytanic acid was increased, whereas pristanic acid was within the control range, resulting in a low pristanic acid/phytanic acid ratio. In the blood spot from a patient with X-linked adrenoleukodystrophy, the concentrations of the acids and their ratio were normal. These findings are consistent with results for these acids in plasma from such patients. Measurement of phytanic acid and pristanic acid and their ratios in stored dried blood collected at neonatal screening can therefore be used in the diagnosis of peroxisomal disorders, especially for those cases in which, owing to early death of the patient, no other material is available for biochemical investigations.

A number of valproate adverse reactions are due to its interference with several metabolic pathways, including that of fatty acid oxidation. In order to resolve which mitochondrial enzymes of fatty acid oxidation are inhibited by which VPA intermediates we have developed methods to synthesize their CoA ester forms. This paper describes the synthesis of VPA acyl-CoA ester metabolites as well as data on the fate of VPA in rat liver mitochondria. Valproyl-CoA, Delta2-valproyl-CoA, and 3-OH-valproyl-CoA were obtained through chemical synthesis. 3-Keto-valproyl-CoA was prepared by a novel enzymatic procedure followed by a combination of solid-phase extraction and preparative HPLC purification. This approach proved to be efficient in obtaining all the beta-oxidation intermediates of valproyl-CoA. The synthetic standards were used for the determination of intramitochondrial concentrations of valproyl-CoA, Delta2-valproyl-CoA, 3-OH-valproyl-CoA, and 3-keto-valproyl-CoA by HPLC. These levels were determined after incubation of intact rat liver mitochondria with VPA under conditions of state 3 and state 4 respiration. The results show that valproyl-CoA and to a much lesser extent 3-keto-valproyl-CoA are the main metabolites of VPA in mitochondria. This information will be of great use in resolving the mechanisms involved in the inhibition of mitochondrial processes like fatty acid oxidation by VPA.

A gas chromatography-mass spectrometry (GC-MS) method is described for the quantification of guanidinoacetate in different body fluids, using a two step derivatisation procedure which involves a reaction with hexafluoroacetylacetone to form a bis(trifluoromethyl)pyrimidine ring structure followed by a reaction with pentafluorobenzyl bromide. 13C2-labelled guanidinoacetate is used as an internal standard. Bis(trifluoromethyl)pyrimidine pentafluorobenzyl derivatives were separated on a polar capillary GC-column and were quantified using negative chemical ionisation mass fragmentography. The detection limit of the method is 1 pmol guanidinoacetate in a 100 μl sample. Control values were obtained for urine (53.9±25.9 mmol mol-1 creatinine), plasma (1.08±0.31 μmol l-1), cerebrospinal fluid (CSF) (0.114±0.068 μmol l-1) and amniotic fluid (3.44±0.64 μmol l-1). The applicability of the method is illustrated by the determination of guanidinoacetate in urine, plasma and CSF of a patient affected with guanidinoacetate methyltransferase deficiency. In all body fluids of this patient, guanidinoacetate was highly elevated. Copyright (C) 1998 Elsevier Science B.V.

In this paper we describe the identification of pristanoyl-CoA oxidase activity in rat liver peroxisomes. This activity was not stimulated by clofibrate feeding. Furthermore, the activity was found in multiple tissues. These results show that pristanoyl-CoA oxidase is different from any of the known oxidases which include a clofibrate-inducible acyl-CoA oxidase and the recently identified cholestanoyl-CoA oxidase. Gelfiltration and chromatofocusing experiments provide conclusive evidence that we are dealing with a novel acyl-CoA oxidase with a unique function in peroxisomal β-oxidation.