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N M Verhoeven

Publications and source records attributed to N M Verhoeven.

51 records · Page 3Linked to original sources
PubMed1998

Clinical approach to inherited peroxisomal disorders: a series of 27 patients.

To illustrate the clinical and biochemical heterogeneity of peroxisomal disorders, we report our experience with 27 patients seen personally between 1982 and 1997. Twenty patients presented with a phenotype corresponding either to Zellweger syndrome, neonatal adrenoleukodystrophy, or infantile Refsum disease, 3 of whom had a peroxisomal disorder due to a single enzyme defect. One patient had a mild form of rhizomelic chondrodysplasia punctata, 1 had classic Refsum disease. Finally, 5 patients presented with clinical manifestations that were either unusually mild or completely atypical, and initially did not arouse suspicion of a peroxisomal disorder. They showed multiple defects of peroxisomal functions with one or several functions remaining intact, suggesting a peroxisome biogenesis disorder. The defect in peroxisome biogenesis was further characterized by variable expression in different tissues and/or individual cells in 5 patients. Studies restricted to fibroblasts failed to identify abnormalities in this group. We demonstrate that clinical manifestations of peroxisomal disorders may be very mild or completely atypical, and therefore, peroxisomal disorders should be considered in a variety of clinical settings. Furthermore, we suggest performing extensive peroxisomal investigations in every patient suspected of suffering from a peroxisomal disorder, even when the clinical presentation is typical.

Adult↗
PubMed1998

An accurate stable isotope dilution gas chromatographic-mass spectrometric approach to the diagnosis of guanidinoacetate methyltransferase deficiency.

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 microl sample. Control values were obtained for urine (53.9 +/- 25.9 mmol mol(-1) creatinine), plasma (1.08 +/- 0.31 micromol l(-1)), cerebrospinal fluid (CSF) (0.114 +/- 0.068 micromol l(-1)) and amniotic fluid (3.44 +/- 0.64 micromol 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.

Amino Acid Metabolism, Inborn Errors↗
PubMed1998

Studies on the oxidation of phytanic acid and pristanic acid in human fibroblasts by acylcarnitine analysis.

The alpha-oxidation of phytanic acid and the beta-oxidation of pristanitc acid were investigated in cultured fibroblasts from controls and patients affected with different peroxisomal disorders using deuterated substrates. Formation of [omega-2H6]4,8-dimethylnonanoylcarnitine ([omega-2H6]C11-carnitine) from [omega-2H6]phytanic acid and [omega-2H6]pristanic acid was used as marker for these processes. Analysis was performed by tandem mass spectrometry. In normal cells, formation of [omega-2H6]C11-carnitine from both [omega-2H6]phytanic acid and [omega-2H6]pristanic acid was observed. When peroxisome-deficient fibroblasts were incubated with these substrates, [omega-2H6]C11-carnitine was not detectable or, in two cases, very low, which results from deficiencies in both peroxisomal alpha- and beta-oxidation. In cells with an isolated beta-oxidation defect at the level of the peroxisomal bifunctional protein, formation of [omega-2H6]C11-carnitine could also not be detected. Cells with an isolated defect in the alpha-oxidation of phytanic acid, obtained from patients affected with Refsum disease (McKusick 266500) or rhizomelic chondrodysplasia punctata (McKusick 215100), did not form [omega-2H6]C11-carnitine from [omega-2H6]phytanic acid. The observed formation of [omega-2H6]C11-carnitine from [omega-2H6]pristanic acid in these cells is in accordance with a normal peroxisomal beta-oxidation in these disorders. This study shows that separate incubation of fibroblasts with [omega-2H6]phytanic acid and [omega-2H6]pristanic acid, followed by acylcarnitine analysis in the medium by tandem mass spectrometry, can be used for screening cell lines for deficiencies in the peroxisomal alpha- and beta-oxidation pathways. Phytanic acid (3,7,11,15-tetramethylhexadecanoic acid) and pristanic acid (2,6,10,14-tetramethylpentadecanoic acid) are branched-chain fatty acids that are constituents of the human diet. As phytanic acid possesses a beta-methyl group, it cannot be degraded by beta-oxidation. Instead, phytanic acid is first degraded by alpha-oxidation, yielding pristanic acid, which is subsequently degraded by beta-oxidation (Figure 1). Phytanic acid alpha-oxidation is thought to occur partly, and pristanic acid beta-oxidation exclusively, in peroxisomes (see Wanders et al 1995 for review). Accumulation of phytanic acid and pristanic acid is found in blood and tissues of patients affected with generalized peroxisomal disorders. In this type of disorder, no morphologically distinguishable peroxisomes are present in tissues, resulting in accumulation of metabolites that are normally metabolized in these organelles (see Wanders et al 1995 for review). The group of generalized peroxisomal disorders consists of three diseases, differing in clinical presentation. Patients suffering from the most severe disease, Zellweger syndrome (McKusick 214100), have symptoms from birth on and usually do not live beyond their first year of life. Neonatal adrenoleukodystrophy (N-ALD, McKusick 202370) has a milder presentation, whereas infantile Refsum disease (IRD, McKusick 266510) is the mildest form among the generalized peroxisomal disorders. Not only in these generalized peroxisomal disorders, but also in some isolated peroxisomal beta-oxidation defects, elevated levels of phytanic acid and pristanic acid are found (ten Brink et al 1992a). The elevated phytanic acid levels are considered to be caused by product inhibition of alpha-oxidation by accumulating pristanic acid. This is reflected in a highly elevated pristanic acid to phytanic acid ratio in plasma from patients suffering from bifunctional protein deficiency or peroxisomal thiolase deficiency (ten Brink et al 1992a). Elevated phytanic acid concentrations are also found in plasma from patients affected with classical Refsum disease and rhizomelic chondrodysplasia punctata (RCDP). As pristanic acid beta-oxidation is not disturbed in these disorders, pristanic acid levels are normal (ten Brink et al 1992

Carnitine↗
PubMed1998

The metabolism of phytanic acid and pristanic acid in man: a review.

The branched-chain fatty acid phytanic acid is a constituent of the diet, present in diary products, meat and fish. Degradation of this fatty acid in the human body is preceded by activation to phytanoyl-CoA and starts with one cycle of alpha-oxidation. Intermediates in this pathway are 2-hydroxy-phytanoyl-CoA and pristanal; the product is pristanic acid. After activation, pristanic acid is degraded by peroxisomal beta-oxidation. Several disorders have been described in which phytanic acid accumulates, in some cases in combination with pristanic acid. In classical Refsum disease, the enzyme that converts phytanoyl-CoA into 2-hydroxyphytanoyl-CoA--phytanoyl-CoA hydroxylase--is deficient, resulting in highly elevated levels of phytanic acid in blood and tissues. Also in rhizomelic chondrodysplasia punctata, phytanic acid accumulates, owing to a deficiency in the peroxisomal import of proteins with a peroxisomal targeting sequence type 2. In patients affected with generalized peroxisomal disorders, degradation of both phytanic acid and pristanic acid is impaired owing to absence of functional peroxisomes. In bifunctional protein deficiency, the disturbed oxidation of pristanic acid results in elevated levels of this fatty acid and a secondary elevation of phytanic acid. In addition, several variant peroxisomal disorders with unknown aetiology have been described in which phytanic acid and/or pristanic acid accumulate. This review describes the discovery of phytanic acid and pristanic acid and the initial attempts to elucidate the origins and fates of these fatty acids. The current knowledge on the alpha-oxidation and beta-oxidation of these branched-chain fatty acids is summarized. The disorders in which phytanic acid and/or pristanic acid accumulate are described and some remarks are made on the pathogenic mechanisms of elevated levels of phytanic acid and pristanic acid.

Animals↗
PubMed1998

Defective peroxisome biogenesis with a neuromuscular disorder resembling Werdnig-Hoffmann disease.

OBJECTIVE: Characterization of the defect in a patient presenting a peripheral neuropathy with atypical features of distal motor involvement mimicking Werdnig-Hoffmann disease. PATIENT: Clinical signs included generalized hypotonia and floppiness, absence of stretch reflexes, muscle wasting, lack of head control and lingual fasciculations associated with unaffected facial muscles, and normal intellectual development. RESULTS: Normal muscle histology ruled out Werdnig-Hoffmann disease. Elevated plasma concentrations of very long-chain fatty acids and bile acid intermediates combined with normal plasmalogen levels in erythrocytes suggested defective peroxisomal beta-oxidation directly demonstrated by deficient pristanic acid and partially deficient C26:0 was present oxidation in cultured fibroblasts. Severely impaired pipecolic acid oxidation in liver and phytanic acid oxidation in fibroblasts was present. On light and electron microscopy of the liver tissue, rare peroxisomal membrane ghosts and trilamellar inclusions but absence of peroxisomes was noted. Immunoblot analysis revealed absence of peroxisomal beta-oxidation enzymes in liver tissue but normal results in fibroblasts. Remarkably, expression of the peroxisomal defect in fibroblasts was indicated by the finding of mainly cytoplasmatic catalase, as in liver. Preliminary studies excluded classification of this patient within the large PEX1 complementation group. CONCLUSIONS: The results suggest a novel peroxisome biogenesis disorder involving peroxisomal beta-oxidation as well as phytanic and pipecolic acid oxidation rather than an isolated defect of peroxisomal beta-oxidation. The association of a clinical picture mimicking Werdnig-Hoffmann disease with a novel peroxisomal disorder raises the question of whether investigation for peroxisomal function should be considered in every patient with an enigmatic spinal muscular atrophy-like syndrome.

Bile Acids and Salts↗
PubMed1998

Phytanic acid and pristanic acid are oxidized by sequential peroxisomal and mitochondrial reactions in cultured fibroblasts.

The relationship between peroxisomal and mitochondrial oxidation of the methyl branched fatty acids, phytanic acid and pristanic acid, was studied in normal and mutant human skin fibroblasts with established enzyme deficiencies. Tandem mass spectrometry was used for analysis of the acylcarnitine intermediates. In normal cells, 4,8-dimethylnonanoylcarnitine (C11:0) and 2,6-dimethylheptanoylcarnitine (C9:0) accumulated after incubation with either phytanic acid or pristanic acid. These intermediates were not observed when peroxisome-deficient cells from Zellweger patients were incubated with the same compounds, pointing to the involvement of peroxisomes in the formation of these acylcarnitine intermediates. Similar experiments with fibroblasts deficient in carnitine palmitoyltransferase I, carnitine-acylcarnitine translocase or carnitine palmitoyltransferase II revealed that mitochondrial carnitine palmitoyltransferase I is not required for the oxidation of phytanic acid or pristanic acid, whereas both carnitine-acylcarnitine translocase and carnitine palmitoyltransferase II are necessary. These studies demonstrate that both phytanic acid and pristanic acid are initially oxidized in peroxisomes to 4,8-dimethylnonanoyl-CoA, which is converted to the corresponding acylcarnitine (presumably by peroxisomal carnitine octanoyltransferase), and exported to the mitochondrion. After transport across the mitochondrial membrane and transfer of the acylgroup to coenzyme A, further oxidation to 2,6-dimethylheptanoyl-CoA occurs.

Carnitine Acyltransferases↗
PubMed1997

Phytanic acid alpha-oxidation in peroxisomal disorders: studies in cultured human fibroblasts.

We studied the alpha-oxidation of phytanic acid in human fibroblasts of controls and patients affected with classical Refsum disease, rhizomelic chondrodysplasia punctata, generalized peroxisomal disorders and peroxisomal bifunctional protein deficiency. Cultured fibroblasts were incubated with phytanic acid, after which medium and cells were collected separately. 2-Hydroxyphytanic acid and pristanic acid were measured in the medium and cells by stable isotope dilution gas chromatography mass spectrometry. In controls, 2-hydroxyphytanic acid and pristanic acid could be detected in the medium after incubation with phytanic acid, proving that alpha-oxidation of phytanic acid via 2-hydroxyphytanoyl-CoA to pristanic acid was active and intermediates were excreted into the medium. In cells from patients with a defective alpha-oxidation (Refsum disease, rhizomelic chondrodysplasia punctata and generalized peroxisomal disorders) 2-hydroxyphytanic acid and pristanic acid were low or not detectable, showing that in these disorders the hydroxylation of phytanoyl-CoA to 2-hydroxyphytanoyl-CoA is deficient. In cells with a peroxisomal beta-oxidation defect, 2-hydroxyphytanic acid and pristanic acid were formed in amounts comparable to those in the controls.

Cells, Cultured↗
PubMed1997

Resolution of the phytanic acid alpha-oxidation pathway: identification of pristanal as product of the decarboxylation of 2-hydroxyphytanoyl-CoA.

The structure and enzymology of the phytanic acid alpha-oxidation pathway have long remained an enigma. Recent studies have shown that phytanic acid first undergoes activation to its coenzyme A ester, followed by hydroxylation to 2-hydroxyphytanoyl-CoA. In this paper we have studied the mechanism of decarboxylation of 2-hydroxyphytanoyl-CoA in human liver. To this end, human liver homogenates were incubated with 2-hydroxyphytanoyl-CoA in the presence or absence of NAD+. Hereafter, the medium was analyzed for the presence of pristanal and pristanic acid by gas chromatography mass spectrometry. Our results show that pristanal is formed from 2-hydroxyphytanoyl-CoA. Pristanal is subsequently oxidized to pristanic acid in a NAD+ dependent reaction. These results finally resolve the mechanism of the phytanic acid alpha-oxidation process in human liver.

Aldehydes↗
PubMed1997

Stable isotope studies of phytanic acid alpha-oxidation: in vivo production of formic acid.

The aim of this study was to test whether formate is formed during alpha-oxidation of phytanic acid in humans. To a healthy volunteer, [1-13C]phytanic acid was given as an oral substrate in a dose of 15 mg/kg body weight, after which plasma, urine and breath air samples were collected during 35 h. The plasma concentrations of [1-13C]-phytanic acid, 2-hydroxy[1-13C]phytanic acid, pristanic acid and [13C]formate were analysed. The [1-13C]phytanic acid concentration increased within 5-7 h to 105 mumol/l, then decreased. Formation of 2-hydroxy[1-13C]phytanic acid increased during the first 11 h after which it decreased during the next 20 h. Pristanic acid increased slightly during the test. In breath air, 13CO2 enrichment was measured, showing a cumulative output of ca. 30% of the ingested dose after 35 h. In both urine and plasma, enrichment of [13C]formate, higher than that of 13CO2 was demonstrated. These findings show that formate is a decarboxylation product in the alpha-oxidation of phytanic acid in vivo.

Adult↗
PubMed1997

Phytanic acid alpha-oxidation: decarboxylation of 2-hydroxyphytanoyl-CoA to pristanic acid in human liver.

The degradation of the first intermediate in the alpha-oxidation of phytanic acid, 2-hydroxyphytanoyl-CoA, was investigated. Human liver homogenates were incubated with 2-hydroxyphytanoyl-CoA or 2-hydroxyphytanic acid, after which formation of 2-ketophytanic acid and pristanic acid were studied. 2-Hydroxyphytanic acid was converted into 2-ketophytanic acid and pristanic acid. When ATP, Mg2+, and coenzyme A were added to the incubation medium, higher amounts of pristanic acid were formed, whereas the formation of 2-ketophytanic acid strongly decreased. When 2-hydroxyphytanoyl-CoA was used as substrate, there was virtually no 2-ketophytanic acid formation. However, pristanic acid was formed in higher amounts than with 2-hydroxyphytanic acid as substrate. This reaction was stimulated by NAD+ and NADP+. Pristanic acid, and not pristanoyl-CoA was found to be the product of the reaction. These results suggest the existence of two pathways for decarboxylation of 2-hydroxyphytanic acid. The first one, starting from 2-hydroxyphytanic acid, involves the formation of 2-ketophytanic acid with only a small amount of pristanic acid being formed. The second pathway, which starts from 2-hydroxyphytanoyl-CoA, does not involve 2-ketophytanic acid and generates higher amounts of pristanic acid. The first pathway, which is peroxisomally localized, was found to be deficient in Zellweger syndrome, whereas the second pathway, localized in microsomes, was normally active. We conclude that the second pathway is predominant under in vivo conditions.

Biomarkers↗
PubMed1995

Pre- and postnatal diagnosis of peroxisomal disorders using stable-isotope dilution gas chromatography--mass spectrometry.

Quantitative analysis of the following peroxisomal metabolites is reported: very long-chain fatty acids (VLCFA), pipecolic acid, bile acid intermediates, phytanic and pristanic acid, in plasma, urine, cerebrospinal fluid (CSF), blood spots collected at neonatal screening and amniotic fluid. An overview is given of the concentrations of these metabolites in body fluids from control subjects and all patients investigated so far in this laboratory. The method of choice is gas chromatography -- mass spectrometry (GC-MS) with electron capture detection, combined with the use of stable-isotope-labelled internal standards.

Amniotic Fluid↗
PubMed1993

Cloning of the cDNA coding for 14 kDa group II phospholipase A2 from rat liver.

The amino acid sequence of rat liver phospholipase A2 was partially elucidated using peptide fragments generated by enzymatic or chemical cleavage. Based on this sequence information, two oligonucleotide probes were constructed which were applied in a polymerase chain reaction on cDNA generated from rat liver total RNA. This resulted in cloning of the cDNA corresponding to the coding region of the mature phospholipase A2. The deduced amino acid sequence showed the enzyme belongs to the group II phospholipases, and is almost completely identical to rat platelet and spleen membrane-associated phospholipase A2. However, in the cDNA isolated one codon was different as compared to the platelet and spleen enzymes, resulting in the substitution of Ala94 by Arg94 in the liver enzyme. In Northern blot analyses the mRNA for rat group II phospholipase A2 could not be detected in rat liver, neither in total RNA nor in poly(A)+ RNA. However, a polymerase chain reaction using total RNA originating from freshly isolated hepatocytes resulted in the amplification of the described phospholipase A2 cDNA. This indicates that group II PLA2 mRNA is present in these cells, but presumably at very low abundance. The observed increase in rat group II phospholipase A2 secretion in rat mesangial cells upon stimulation with interleukin-1 beta (Pfeilschifter et al. (1989), Biochem. Biophys. Res. Commun. 159, 385-394) was shown to be accompanied by an increased transcription of the rat group II phospholipase A2 gene, indicating interleukin exerts its effect via increased phospholipase A2 mRNA synthesis. Based on Northern blot analyses of stimulated rat mesangial cells, the size of the mRNA for rat group II phospholipase A2 was determined to be 0.9 kb.

Amino Acid Sequence↗
PubMedDate not supplied

L-Arabinosuria: a new defect in human pentose metabolism.

A female patient, the first child of healthy non-consanguineous parents, presented at the age of 16 months with delayed motor development and facial dysmorphism. In addition she displayed a palatoschizis and multiple skeletal abnormalities as hypoplastic scapulae, hypoplastic os ilea, and an extreme cervical kyphosis. Biochemical investigation of urine revealed no abnormalities except for the presence of large amounts of reducing sugars. The sugar was identified as L-arabinose, which mainly originated from fruit formula in her diet. In addition highly elevated levels of L-arabitol were found in urine, plasma, and cerebrospinal fluid. Although little is known about human arabinose metabolism, we presume that L-arabitol dehydrogenase is deficient in our patient. As polyols are potentially toxic to the central nervous system there could be deleterious long-term effects of this disorder. Withdrawal of dietary fruit led to normalization of polyol levels. The above-mentioned clinical abnormalities are probably not related to this new inborn error of metabolism and should be considered as a separate entity.

Arabinose↗