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X-linked adrenoleukodystrophy (X-ALD) is a fatal, axonal demyelinating, neurometabolic disease. It results from the functional loss of a member of the peroxisomal ATP-binding cassette transporter subfamily D (ABCD1), which is involved in the metabolism of very long-chain fatty acids (VLCFA). Oxidative damage of proteins caused by excess of the hexacosanoic acid, the most prevalent VLCFA accumulating in X-ALD, is an early event in the neurodegenerative cascade. We demonstrate here that valproic acid (VPA), a widely used anti-epileptic drug with histone deacetylase inhibitor properties, induced the expression of the functionally overlapping ABCD2 peroxisomal transporter. VPA corrected the oxidative damage and decreased the levels of monounsaturated VLCFA (C26:1 n-9), but not saturated VLCFA. Overexpression of ABCD2 alone prevented oxidative lesions to proteins in a mouse model of X-ALD. A 6-month pilot trial of VPA in X-ALD patients resulted in reversion of the oxidative damage of proteins in peripheral blood mononuclear cells. Thus, we propose VPA as a promising novel therapeutic approach that warrants further clinical investigation in X-ALD. This work was supported by grants from the European Commission (LSHM-CT2004-502987 and FP7-241622), the European Leukodystrophy Association (ELA 2006-043I4), the Spanish Institute for Health Carlos III (FIS PI080991 and FIS PI051118) and the Autonomous Government of Catalonia (2009SGR85) to A.P. S.F. was a fellow of the European Leukodystrophy Association (ELA 2007-018F4). S.K. also received a grant from the European Leukodystrophy Association (ELA 2006-031I4). The work was developed under the COST action BM0604 (to A.P.). The CIBER de Enfermedades Raras is an initiative of the ISCIII. Work carried out at the Department of Experimental Medicine was supported in part by I + D grants from the Spanish Ministry of Science and Innovation (AGL2006-12433 and BFU2009-11879/BFI), the Spanish Ministry of Health (RD06/0013/0012 and PI081843), the Autonomous Government of Catalonia (2009SGR735), ‘La Caixa’ Foundation and COST B35 Action from the European Union. A.N. received a predoctoral fellowship from ‘La Caixa’ Foundation.

Very-long-chain fatty acids (VLCFAs) have long been known to be degraded exclusively in peroxisomes via beta-oxidation. A defect in peroxisomal beta-oxidation results in elevated levels of VLCFAs and is associated with the most frequent inherited disorder of the central nervous system white matter, X-linked adrenoleukodystrophy. Recently, we demonstrated that VLCFAs can also undergo omega-oxidation, which may provide an alternative route for the breakdown of VLCFAs. The omega-oxidation of VLCFA is initiated by CYP4F2 and CYP4F3B, which produce omega-hydroxy-VLCFAs. In this article, we characterized the enzymes involved in the formation of very-long-chain dicarboxylic acids from omega-hydroxy-VLCFAs. We demonstrate that very-long-chain dicarboxylic acids are produced via two independent pathways. The first is mediated by an as yet unidentified, microsomal NAD(+)-dependent alcohol dehydrogenase and fatty aldehyde dehydrogenase, which is encoded by the ALDH3A2 gene and is deficient in patients with Sjogren-Larsson syndrome. The second pathway involves the NADPH-dependent hydroxylation of omega-hydroxy-VLCFAs by CYP4F2, CYP4F3B, or CYP4F3A. Enzyme kinetic studies show that oxidation of omega-hydroxy-VLCFAs occurs predominantly via the NAD(+)-dependent route. Overall, our data demonstrate that in humans all enzymes are present for the complete conversion of VLCFAs to their corresponding very-long-chain dicarboxylic acids.

Phytol is a branched-chain fatty alcohol that is a naturally occurring precursor of phytanic acid, a fatty acid involved in the pathogenesis of Refsum disease. The conversion of phytol into phytanic acid is generally believed to take place via three enzymatic steps that involve 1) oxidation to its aldehyde, 2) further oxidation to phytenic acid, and 3) reduction of the double bond at the 2,3 position, yielding phytanic acid. Our recent investigations of this mechanism have elucidated the enzymatic steps leading to phytenic acid production, but the final step of the pathway has not been investigated so far. In this study, we describe the characterization of phytenic acid reduction in rat liver. NADPH-dependent conversion of phytenic acid into phytanic acid was detected, although at a slow rate. However, it was shown that phytenic acid can be activated to its CoA ester and that reduction of phytenoyl-CoA is much more efficient than that of phytenic acid. Furthermore, in rat hepatocytes cultured in the presence of phytol, phytenoyl-CoA could be detected, showing that it is a bona fide intermediate of phytol degradation. Subcellular fractionation experiments revealed that phytenoyl-CoA reductase activity is present in peroxisomes and mitochondria. With these findings, we have accomplished the full elucidation of the mechanism by which phytol is converted into phytanic acid.

Dicarboxylic acids (DCAs) are omega-oxidation products of monocarboxylic acids. After activation by a dicarboxylyl-CoA synthetase, the dicarboxylyl-CoA esters are shortened via beta-oxidation. Although it has been studied extensively where this beta-oxidation process takes place, the intracellular site of DCA oxidation has remained controversial. Making use of fibroblasts from patients with defined mitochondrial and peroxisomal fatty acid oxidation defects, we show in this paper that peroxisomes, and not mitochondria, are involved in the beta-oxidation of C16DCA. Additional studies in fibroblasts from patients with X-linked adrenoleukodystrophy, straight-chain acyl-CoA oxidase (SCOX) deficiency, d-bifunctional protein (DBP) deficiency, and rhizomelic chondrodysplasia punctata type 1, together with direct enzyme measurements with human recombinant l-bifunctional protein (LBP) and DBP expressed in a fox2 deletion mutant of Saccharomyces cerevisiae, show that the main enzymes involved in beta-oxidation of C16DCA are SCOX, both LBP and DBP, and sterol carrier protein X, possibly together with the classic 3-ketoacyl-CoA thiolase. This is the first indication of a specific function for LBP, which has remained elusive until now.

D-bifunctional protein (D-BP) plays an indispensable role in peroxisomal beta-oxidation, and its inherited deficiency in humans is associated with severe clinical abnormalities. Three different subtypes of D-BP deficiency can be distinguished: 1) a complete deficiency of D-BP (type I), 2) an isolated D-BP enoyl-CoA hydratase deficiency (type II), and 3) an isolated D-BP 3-hydroxyacyl-CoA dehydrogenase deficiency (type III). In this study, we developed a method to measure D-BP dehydrogenase activity independent of D-BP hydratase (D-BP HY) activity to distinguish between D-BP deficiency type I and type II, which until now was only possible by mutation analysis. For this assay, the hydratase domain of D-BP was expressed in the yeast Saccharomyces cerevisiae. After a coincubation of yeast homogenate expressing D-BP HY with fibroblast homogenate of patients using the enoyl-CoA ester of the bile acid intermediate trihydroxycholestanoic acid as substrate, D-BP dehydrogenase activity was measured. Fibroblasts of patients with a D-BP deficiency type II displayed D-BP dehydrogenase activity, whereas type I and type III patients did not. This newly developed assay to measure D-BP dehydrogenase activity in fibroblast homogenates provides a quick and reliable method to assign patients with deficient D-BP HY activity to the D-BP deficiency subgroups type I or type II.

Phytanic acid (3,7,11,15-tetramethylhexadecanoic acid) is a branched-chain fatty acid derived from dietary sources and broken down in the peroxisome to pristanic acid (2,6,10,14-tetramethylpentadecanoic acid) via a -oxidation. Pristanic acid then undergoes b -oxidation in peroxisomes. Phytanic acid naturally occurs as a mixture of (3 S ,7 R ,11 R )- and (3 R ,7 R ,11 R )-diastereomers. In contrast to the a -oxidation system, peroxisomal b -oxidation is stereospecific and only accepts (2 S )-isomers. Therefore, a racemase called a -methyl- acyl-CoA racemase is required to convert (2 R )-pristanic acid into its (2 S )-isomer. To further investigate the stereochemis- try of the peroxisomal oxidation systems and their sub- strates, we have developed a method using gas-liquid chro- matography-mass spectrometry to analyze the isomers of phytanic, pristanic, and trimethylundecanoic acid in plasma from patients with various peroxisomal fatty acid oxidation defects. In this study, we show that in plasma of patients with a peroxisomal b -oxidation deficiency, the relative amounts of the two diastereomers of pristanic acid are al- most equal, whereas in patients with a defect of a -methyl- acyl-CoA racemase, (2 R )-pristanic acid is the predominant isomer. Furthermore, we show that in a -methylacyl-CoA racemase deficiency, not only pristanic acid accumulates, but also one of the metabolites of pristanic acid, (2,6,10)- trimethylundecanoic acid, providing direct in vivo evidence for the requirement of this racemase for the complete degradation of pristanic acid. — Ferdinandusse, S., H. Rusch, A. E. M. van Lint, G. Dacremont, R. J. A. Wanders, and P. Vreken. Stereochemistry of the peroxisomal branched-chain fatty acid a - and b -oxidation systems in pa- tients suffering from different peroxisomal disorders. J. Lipid Res. 2002. 43: 438-444.

α-Methylacyl-CoA racemase plays an important role in the β-oxidation of branched-chain fatty acids and fatty acid derivatives because it catalyzes the conversion of several (2R)-methyl-branched-chain fatty acyl-CoAs to their (S)-stereoisomers. Only stereoisomers with the 2-methyl group in the (S)-configuration can be degraded via β-oxidation. Patients with a deficiency of α-methylacyl-CoA racemase accumulate in their plasma pristanic acid and the bile acid intermediates di- and trihydroxycholestanoic acid, which are all substrates of the peroxisomal β-oxidation system. Subcellular fractionation experiments, however, revealed that both in humans and rats α-methylacyl-CoA racemase is bimodally distributed to both the peroxisome and the mitochondrion. Our findings show that the peroxisomal and mitochondrial enzymes are produced from the same gene and that, as a consequence, the bimodal distribution pattern must be the result of differential targeting of the same gene product. In addition, we investigated the physiological role of the enzyme in the mitochondrion. Both in vitro studies with purified heterologously expressed protein and in vivo studies in fibroblasts of patients with an α-methylacyl-CoA racemase deficiency revealed that the mitochondrial enzyme plays a crucial role in the mitochondrial β-oxidation of the breakdown products of pristanic acid by converting (2R,6)-dimethylheptanoyl-CoA to its (S)-stereoisomer. —Ferdinandusse, S., S. Denis, L. IJlst, G. Dacremont, H. R. Waterham, and R. J. A. Wanders. Subcellular localization and physiological role of α-methylacyl-CoA racemase. J. Lipid Res. 2000. 41: 1890–1896.

Peroxisomes are essential organelles exerting key functions in fatty acid metabolism such as the degradation of very long-chain fatty acids (VLCFAs). VLCFAs accumulate in X-adrenoleukodystrophy (X-ALD), a disease caused by deficiency of the Abcd1 peroxisomal transporter. Its closest homologue, Abcd2, exhibits a high degree of functional redundancy on the catabolism of VLCFA, being able to prevent X-ALD-related neurodegeneration in the mouse. In the search for specific roles of Abcd2, we screened fatty acid profiles in organs and primary neurons of mutant knockout mice lacking Abcd2 in basal conditions and under dietary challenges. Our results indicate that ABCD2 plays a role in the degradation of long-chain saturated and ω9-monounsaturated fatty acids and in the synthesis of docosahexanoic acid (DHA). Also, we demonstrated a defective VLCFA β-oxidation ex vivo in brain slices of Abcd1 and Abcd2 knockouts, using radiolabeled hexacosanoic acid and the precursor of DHA as substrates. As DHA levels are inversely correlated with the incidence of Alzheimer's and several degenerative conditions, we suggest that ABCD2 may act as modulator/modifier gene and therapeutic target in rare and common human disorders.

Several different processes involved in the metabolic fate of docosahexaenoic acid (DHA, C22:6n-3) and its precursor in the biosynthesis route, C24:6n-3, were studied. In cultured skin fibroblasts, the oxidation rate of [1-14C] 24:6n-3 was 2.7 times higher than for [1-14C]22:6n-3, whereas [1-14C]22:6n-3 was incorporated 7 times faster into different lipid classes than was [1-14C]24:6n-3. When determining the peroxisomal acyl-CoA oxidase activity, similar specific activities for C22:6(n-3)-CoA and C24:6(n-3)-CoA were found in mouse kidney peroxisomes. Thioesterase activity was measured for both substrates in mouse kidney peroxisomes as well as mitochondria, and C22:6(n-3)-CoA was hydrolyzed 1.7 times faster than C24:6(n-3)-CoA. These results imply that the preferred metabolic fate of C24:6(n-3)-CoA, after its synthesis in the endoplasmic reticulum (ER), is to move to the peroxisome, where it is beta-oxidized, producing C22:6(n-3)-CoA. This DHA-CoA then preferentially moves back, probably as free fatty acid, to the ER, where it is incorporated into membrane lipids.

Bile acids are synthesized de novo in the liver from cholesterol and conjugated to glycine or taurine via a complex series of reactions involving multiple organelles. Bile acids secreted into the small intestine are efficiently reabsorbed and reutilized. Activation by thioesterification to CoA is required at two points in bile acid metabolism. First, 3alpha,7alpha,12alpha-trihydroxy-5beta-cholestanoic acid, the 27-carbon precursor of cholic acid, must be activated to its CoA derivative before side chain cleavage via peroxisomal beta-oxidation. Second, reutilization of cholate and other C24 bile acids requires reactivation prior to re-conjugation. We reported previously that homolog 2 of very long-chain acyl-CoA synthetase (VLCS) can activate cholate (Steinberg, S. J., Mihalik, S. J., Kim, D. G., Cuebas, D. A., and Watkins, P. A. (2000) J. Biol. Chem. 275, 15605-15608). We now show that this enzyme also activates chenodeoxycholate, the secondary bile acids deoxycholate and lithocholate, and 3alpha,7alpha,12alpha-trihydroxy-5beta-cholestanoic acid. In contrast, VLCS activated 3alpha,7alpha,12alpha-trihydroxy-5beta-cholestanoate, but did not utilize any of the C24 bile acids as substrates. We hypothesize that the primary function of homolog 2 is in the reactivation and recycling of C24 bile acids, whereas VLCS participates in the de novo synthesis pathway. Results of in situ hybridization, topographic orientation, and inhibition studies are consistent with the proposed roles of these enzymes in bile acid metabolism.

Sterol carrier protein X (SCPx) plays a crucial role in the peroxisomal oxidation of branched-chain fatty acids. To investigate whether patients with an unresolved defect in peroxisomal β-oxidation are deficient for SCPx, we developed a novel and specific assay to measure the activity of SCPx in both liver and fibroblast homogenates. The substrate used in the assay, 3α,7α,12α-trihydroxy-24-keto-5β-cholestanoyl-CoA (24-keto-THC-CoA), is produced by preincubating the enoyl-CoA of the bile acid intermediate THCA with a lysate from the yeast Saccharomyces cerevisiae expressing human D-bifunctional protein. After the preincubation period, liver or fibroblast homogenate is added plus CoASH, and the production of choloyl-CoA is determined by HPLC. The specificity of the assay was demonstrated by the finding of a full deficiency in fibroblasts from an SCPx knock-out mouse. In addition to SCPx activity measurements in fibroblasts from patients with a defect in peroxisomal β-oxidation of unresolved etiology, we studied the stability and activity of SCPx in fibroblasts from patients with Zellweger syndrome, which lack functional peroxisomes. We found that SCPx is not only stable in the cytosol, but displays a higher activity in fibroblasts from patients with Zellweger syndrome than in control fibroblasts. Furthermore, in all patients studied with a defect in peroxisomal β-oxidation of unknown origin, SCPx was found to be normally active, indicating that human SCPx deficiency remains to be identified. —Ferdinandusse, S., S. Denis, E. van Berkel, G. Dacremont, and R. J. A. Wanders. Peroxisomal fatty acid oxidation disorders and 58 kDA sterol carrier protein X (SCPx): activity measurements in liver and fibroblasts using a newly developed method. J. Lipid Res. 2000. 41: 336–342

A case of X-linked recessive chondrodysplasia punctata (CP) is described. The finding of a reciprocal X-Y translocation involving the region distal to Xp22.3 and the presence of fluorescent Yp11.23 regions confirms the localization of X-linked recessive CP at p22.3. No gross peroxisomal abnormalities were present in the propositus.

Five brain-derived and 17 urinary oligomannose-type oligosaccharides were isolated by ion-exchange chromatography on Mono Q or Dowex, followed by HPLC on Lichrosorb-NH2 from a Persian cat suffering from alpha-mannosidosis. The structures of the carbohydrate chains were determined by 500- or 600-MHz 1H-NMR spectroscopy. Different oligosaccharide patterns were found in brain and urine. 99% of the urinary oligosaccharides possess an alpha(1-6)-linked mannose residue attached to beta-mannose, whereas only 5% of the brain-derived oligosaccharides contain such a residue. Furthermore, of the urinary carbohydrate chains 71% end with Man beta 1-4GlcNAc beta 1-4GlcNAc and 29% end with Man beta 1-4GlcNAc, whereas the corresponding amounts are 23% and 77%, respectively, for the brain-derived oligosaccharides.

Evidence is given that phenothiazines depress hepatic peroxisomal fatty acid oxidation in vivo. After oral administration to rats thioridazine and chlorpromazine inhibit peroxisomal β-oxidation, evaluated by H2O2 production, during 2 weeks. In mice, this effect could not be demonstrated. However, in both species VLCFA are increased after short and long term drug administration. Electron microscopy reveals the presence of membranous structures in liver cytoplasm or lysosomes. The inhibition by thioridazine of peroxisomal β-oxidation does not lead to hepatic peroxisome proliferation. The activities of enzymes related to fatty acid breakdown are not increased and liver peroxisomes are microscopically normal.