Refsum Disease Research Articles

Biogenesis of peroxisomes in fetal liver.

Peroxisomes are single membrane-limited cell organelles that are involved in numerous metabolic functions. Peroxisomes do not contain DNA; the matrix and membrane proteins are encoded by the nuclear genome. It is assumed that new peroxisomes are formed by division of existing organelles. The present article gives an overview of microscopic studies and recent unpublished results dealing with peroxisome biogenesis in mammalian fetal liver and presents data on peroxisomes in oocytes. Cytochemical (catalase and D-aminoacid oxidase activity) and immunocytochemical data in rat and human liver (antigens of catalase, the three peroxisomal beta-oxidation enzymes, alanine: glyoxylate aminotransferase, peroxisomal membrane proteins with molecular weights of 42 and 70 kDa) indicate that during embryonic and fetal development the peroxisomal population undergoes a differentiation with respect to the composition of the matrix and to the size and number of the organelles. In the youngest stages, rare and small peroxisomes are present, into which the matrix components are imported in a sequential way. The import seems asynchronous in peroxisomes of the same hepatocyte. The size and number of the peroxisomes increase during liver development. In rat and human liver, no morphological or immunocytochemical evidence for an elaborate network of interconnected peroxisomes ("reticulum") was found. Instead, peroxisomes presented as individual organelles, which occasionally show membrane extensions. The importance of the metabolic functions of peroxisomes in human liver is emphasized by the peroxisomal disorders. In the liver of affected fetuses, the microscopic features associated with the defect can already be recognized; i.e., either catalase containing peroxisomes are absent and catalase is localized in the cytoplasm (in fetuses affected with Zellweger syndrome or with infantile Refsum disease) or peroxisomes are present but they are abnormally enlarged (e.g., a fetus affected with acyl-CoA oxidase deficiency). In the quail ovary, numerous peroxisomes are observed in the oocyte and in the granulosa cells during follicle maturation, but not in the full-grown egg. Thus, the mechanism of peroxisome inheritance remains unresolved.

Refsum disease is caused by mutations in the phytanoyl–CoA hydroxylase gene

Refsum disease is an autosomal-recessively inherited disorder characterized clinically by a tetrad of abnormalities: retinitis pigmentosa, peripheral neuropathy, cerebellar ataxia and elevated protein levels in the cerebrospinal fluid (CSF) without an increase in the number of cells in the CSF. All patients exhibit accumulation of an unusual branched-chain fatty acid, phytanic acid (3,7,11,15-tetramethylhexadecanoic acid), in blood and tissues. Biochemically, the disease is caused by the deficiency of phytanoyl-CoA hydroxylase (PhyH), a peroxisomal protein catalyzing the first step in the alpha-oxidation of phytanic acid. We have purified PhyH from rat-liver peroxisomes and determined the N-terminal amino-acid sequence, as well as an additional internal amino-acid sequence obtained after Lys-C digestion of the purified protein. A search of the EST database with these partial amino-acid sequences led to the identification of the full-length human cDNA sequence encoding PhyH: the open reading frame encodes a 41.2-kD protein of 338 amino acids, which contains a cleavable peroxisomal targeting signal type 2 (PTS2). Sequence analysis of PHYH fibroblast cDNA from five patients with Refsum disease revealed distinct mutations, including a one-nucleotide deletion, a 111-nucleotide deletion and a point mutation. This analysis confirms our finding that Refsum disease is caused by a deficiency of PhyH.

Phytanic acid α-oxidation in peroxisomal disorders: Studies in cultured human fibroblasts

We studied the α-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 α-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 α-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 β-oxidation defect, 2-hydroxyphytanic acid and pristanic acid were formed in amounts comparable to those in the controls.

INHERITED PERIPHERAL NEUROPATHIES

BACKGROUND– Peripheral neuropathy may result from diverse genetic causes. In recent years molecular diagnostic methods have clarified the relationships between many of these different causes and their resultant clinical phenotypes. REVIEW SUMMARY– Charcot-Marie-Tooth neuropathy type 1 (CMT 1) (demyelinating CMT) is most commonly associated with a duplication on chromosome 17 (CMT 1 A) and, less frequently, with point mutations within the myelin gene PMP22 (on chromosome 17) or in the myelin protein zero (Po) (on chromosome 1; CMT 1B). Hereditary neuropathy with liability to pressure palsies results from a deletion on chromosome 17p, which is reciprocal to the duplication seen in CMT 1A patients. Dejerine-Sottas disease is a less common, severe, demyelinating neuropathy that has been associated with mutations in either PMP22 or Po. X-linked CMT is associated with mutations in the connexin 32 gene. No candidate genes have been identified in CMT 2, but at least three different forms have been identified by genetic linkage analysis. These forms map to chromosomes 1p, 3, and 7. Refsum's disease, resulting from abnormalities of phytanic acid metabolism, is an autosomal recessive cause of demyelinating neuropathy. Familial amyloid neuropathy (FAP) is a less frequently diagnosed cause of hereditary neuropathy. In many cases, FAP arises from mutations in the transthyretin protein and may be treatable with liver transplantation. Mitochondria) DNA mutations may also lead to peripheral neuropathy, but usually in the context of more generalized mitochondrial illness. CONCLUSIONS– Understanding of the molecular genetics of neuropathies has facilitated patient care by providing direct methods for confirming the diagnosis. This should eventually lead to improved therapy for each particular disorder.

Peroxisomal localization of alpha-oxidation in human liver.

It was found that alpha-oxidation in rat liver is a peroxisomal process, consisting of an activation, a 2-hydroxylation, and a reaction leading to the production of formate. alpha-Oxidation of 3-methyl-substituted fatty acids was quantified by measuring the production of formate and CO2, and the production of a 2-hydroxy-3-methylacyl-CoA-intermediate was demonstrated. We wanted to extend these findings to human liver, in view of the controversy over the subcellular localization of alpha-oxidation in man. In homogenates from human liver, rates of alpha-oxidation were highest when measured in the presence of ATP, CoA, Mg2+, 2-oxoglutarate, ascorbate and Fe2+. In subcellular fractions prepared by differential centrifugation and in fractions obtained after subfractionation of a peroxisome-enriched fraction on a Percoll gradient, production of formate and of a 2-hydroxy-3-methylacyl-CoA intermediate coincided with the peroxisomal marker catalase. In broken fractions, production of CO2 was almost negligible as compared to formate production. We conclude from our findings that in human liver, as in rat liver, alpha-oxidation of 3-methyl-substituted fatty acids is a peroxisomal process, consisting of an activation reaction, a 2-hydroxylation reaction and a reaction or reactions leading to the generation of formate as a primary product which is subsequently converted to CO2. Furthermore activation, 2-hydroxylation and generation of formate appear to be coupled (see Casteels et al 1996). These data demonstrate that Refsum disease should indeed be classified as a peroxisomal disease.

Bile acid profiles in a peroxisomal D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein deficiency.

Bile acid profiles in serum, urine and bile from an infant with a peroxisomal D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein (D-bifunctional protein) deficiency were analyzed by means of gas-liquid chromatography, gas-liquid chromatography-mass spectrometry, and high-performance liquid chromatography. As in such several peroxisomal disorders as Zellweger syndrome, neonatal adrenoleukodystrophy, and infantile Refsum disease, the accumulation of C27-bile acid intermediates was also demonstrated in the infant with D-bifunctional protein deficiency, accounting for 74% of the total bile acids in serum, 59% in urine, and 35% in bile. In addition, the major constituents of the C27-bile acids were (24R,25R)- and (24R,25S)-3alpha,7alpha,12alpha,24-tetrahydroxy-5be ta-cholestanoic acids along with small amounts of their 24S counterparts. Since immunoreactive acyl-CoA oxidase, L-bifunctional protein, and thiolase were all present in the liver, the impairment of the oxidative side-chain cleavage in bile acid biosynthesis is considered to be due to the defect of D-bifunctional protein.

Lipoprotein[a] is not present in the plasma of patients with some peroxisomal disorders

Peroxisomal disorders arise either from defects in the biogenesis of peroxisomes or from the defective synthesis of one or more peroxisomal enzymes. These defects result in metabolic disturbances in peroxisomal beta-oxidation of various fatty acids and derivatives and/or in the biosynthesis of ether lipids. In the current study, lipoprotein levels were determined in plasma samples from patients diagnosed with one of four different peroxisomal disorders. While low density lipoprotein (LDL) levels were found to be within the normal range, lipoprotein[a] (Lp[a]) could not be detected by enzyme-linked immunosorbent assay (ELISA) in plasma from patients with cerebro-hepato-renal (Zellweger) syndrome (ZS) and rhizomelic chondrodysplasia punctata (RCDP). Conversely, Lp[a] was clearly present in control plasma obtained from healthy newborns and from patients affected with one of two other peroxisomal disorders, X-linked adrenoleukodystrophy (X-ALD) and Refsum disease (RD) as determined by ELISA. The lack of Lp[a] in plasma of patients with ZS may result from defective secretion of apolipoprotein[a] (apo[a]) (the distinguishing protein component of Lp[a]), as apo[a] mRNA transcripts were clearly present in ZS livers as assessed by PCR, and intracellular apo[a] protein was detected in total liver homogenates from ZS patients as determined by Western blot analysis. Furthermore, LDL present in the plasma of ZS patients was able to associate with recombinant apo[a] in an in vitro Lp[a] assembly assay.

Refsum's disease: long term treatment preserves sensory nerve action potentials and motor function.

Refsum's disease: long term treatment preserves sensory nerve action potentials and motor function.

Repercusión cardíaca de las enfermedades neuromusculares

Many neuromuscular disorders involve the heart, occasionally with overt clinical disease. Muscular dystrophies (dystrophinopathies, limb girdle muscular dystrophy, Emery-Dreifuss muscular dystrophy, Steinert's myotonic dystrophy), congenital myopathies, inflammatory myopathies and metabolic diseases (glycogenosis, periodic paralysis, mitochondrial diseases) may produce dilated or hypertrophic cardiomyopathy and heart rhythm or conduction disturbances. Furthermore the heart is commonly involved in some hereditary and degenerative diseases (Friedreich's ataxia and Kugelberg-Welander syndrome) and acquired (Guillain-Barré syndrome) or inherited (Refsum's disease and Charcot-Marie-Tooth syndrome) polyneuropathies. A cardiologist's high clinical suspicion and a simple but systematic skeletal muscle and peripheral nerve investigation, including muscle enzymes quantification, neurophysiological study and muscle biopsy, are necessary for an accurate diagnosis. In selected patients, more sophisticated biochemical and genetic analysis will be necessary. In most cases, endomyocardial biopsy is not essential for the diagnosis.

The optimized use of gas chromatography-mass spectrometry and high performance liquid chromatography to analyse the serum bile acids of patients with metabolic cholestasis and peroxisomal disorders.

We have measured the bile acids in human serum as methyl ester-trimethylsilyl ethers by gas chromatography-mass spectrometry (GC-MS) using an electron ionization procedure. The overall method was validated and the detection limit (0.4 mumol/l), linearity (2-30 mumol/l), intra-day and inter-day precision, accuracy and recovery (96.2% for nor-23-deoxycholic acid as internal standard) were measured. Serum C24-bile acids profiles from 43 cholestatic patients were measured by GC-MS and by HPLC. The results obtained with the two methods were well correlated and the criteria for selecting either HPLC or GC-MS identified. The serum C24- and C27-bile acids and C29 dicarboxylic bile acid profiles for patients with generalized peroxisomal deficiencies, like Zellweger syndrome (n = 5), neonatal adrenoleukodystrophy (n = 1), infantile Refsum disease (n = 2) and from a single peroxisomal deficiency (n = 1) were also measured by GC-MS.

Phytanic acid activation in rat liver peroxisomes is catalyzed by long-chain acyl-CoA synthetase

In Refsum disease, disorders of peroxisome biogenesis, and rhizomelic chondrodysplasia punctata, pathological accumulation of phytanic acid results from impaired alpha-oxidation of this branched-chain fatty acid. Previous studies from this laboratory indicated that activation of phytanic acid to its CoA derivative precedes its alpha-oxidation in peroxisomes. It was reported that this reaction is catalyzed by a unique phytanoyl-CoA synthetase in human peroxisomes. We wanted to determine whether phytanic acid activation in rats required long-chain acyl-CoA synthetase (LCS), very long-chain acyl-CoA synthetase (VLCS), or a different enzyme. To test directly whether LCS could activate phytanic acid, rat liver cDNA encoding this enzyme was transcribed and translated in vitro. The expressed enzyme had both LCS activity (assayed with palmitic acid, C16: 0) and phytanoyl-CoA synthetase activity; VLCS activity (assayed with lignoceric acid, C24: 0) was not detectable. The ratio of phytanoyl-CoA synthetized activity to palmitoyl-CoA synthetase activity for LCS synthetized in vitro (approximately 205) was higher than that observed in peroxisomes isolated from rat liver (5-10%), suggesting that the expressed enzyme contained sufficient phytanoyl-Coa synthetase activity to account for all activity observed in intact peroxisomes. Further experiments were carried out to verify that phytanic acid was activated by LCS in rat liver peroxisomes. Attempts to separate LCS from phytanoyl-CoA synthetase by chromatography on several matrices were unsuccessful. Preparative isoelectric focusing revealed that phytanoyl-CoA synthetase and LCS had indistinguishable isoelectric points. Phytanoyl-CoA synthetase activity was inhibited by unlabeled palmitic acid but not by lignoceric acid. Heat treatment inactivated both phytanoyl-CoA and palmitoyl-CoA synthetase activities at similar rates. 5,8,11,14-Eicosatetraynoic acid inhibited activation of phytanic acid and palmitic acid in a parallel dose-dependent manner, whereas activation of lignoceric acid was not affected. These data support our conclusion that rat liver LCS, an enzyme known to be present in peroxisomal membranes, has phytanoyl-CoA synthetase activity.

Lipapheresis: an immunoglobulin-sparing treatment for Refsum's disease.

Toxic phytanic acid concentrations in patients with Refsum's disease can be reduced by plasma separation, performed either as plasmapheresis, or as cascade filtration. The latter procedure is as efficient and safe as plasmapheresis, and eliminates the need for albumin replacement. This study investigates the loss of immunoglobulins associated with the procedure. Immunoglobulin- and phytanic acid serum concentrations before and after cascade filtration (n = 16) were measured in a patient with Refsum's disease and their removal determined. Filters with sieving coefficients for immunoglobulin G of 70% and 30% were compared with each other and with historical data on plasmapheresis. While differences in immunoglobulin M loss are negligible, the loss of immunoglobulin G in cascade filtration is significantly less than that reported for plasmapheresis and depends upon the pore size of the employed filters. The loss is least with larger pore size, but this advantage becomes statistically insignificant if immunoglobulin G loss is related to the lesser decrease in phytanic acid concentration that was achieved simultaneously in this study. Unless transplantation of a-hydroxylase containing tissue can be established as treatment for Refsum's disease, cascade filtration appears to be the treatment of choice in order to avoid loss of albumin and to reduce the loss of immunoglobulin G.

Do you know anyone with Refsums disease?

Do you know anyone with Refsums disease?

Phytanic acid oxidation: normal activation and transport yet defective alpha-hydroxylation of phytanic acid in peroxisomes from Refsum disease and rhizomelic chondrodysplasia punctata

In humans the oxidation of phytanic acid is a peroxisomal function. To understand the possible mechanisms for the pathognomic accumulation of phytanic acid in plasma and body fluids of Refsum disease (RD) and rhizomelic chondrodysplasia punctata (RCDP), we investigated activities of various steps (activation, transport, and oxidation) in the metabolism of phytanic acid in peroxisomes isolated from cultured skin fibroblasts from control, RD, and RCDP subjects. Activation of phytanic acid was normal in peroxisomes from both RD and RCDP. Transport of phytanic acid or phytanoyl-CoA in the absence or presence of fatty acid activating cofactors (ATP, MgCl2, and CoASH) into peroxisomes isolated from RD and RCDP skin fibroblasts was also similar to that of peroxisomes from control fibroblasts. Defective oxidation of [(2,3)-3H]- or [1-14C]phytanic acid, or [1-14C]phytanoyl-CoA (substrate for the first step of alpha-oxidation) but normal oxidation of [1-14C] alpha-hydroxyphytanic acid (substrate for the second step of the alpha-oxidation pathway) in peroxisomes from RD clearly demonstrates that excessive accumulation of phytanic acid in plasma and body fluids of RD is due to the deficiency of phytanic acid alpha-hydroxylase in peroxisomes. However, in RCDP peroxisomes, in addition to deficient oxidation of [1-14C]phytanic acid or phytanoyl-CoA or [(2,3)-3H]phytanic acid, the oxidation of [1-14C] alpha-hydroxyphytanic acid was also deficient, indicating that in RCDP the activities both of alpha-hydroxylation of phytanic acid and decarboxylation of alpha-hydroxyphytanic acid are deficient. These observations indicate that peroxisomal membrane functions (phytanic acid activation and transport) in phytanic acid metabolism are normal in both RD and RCDP. The defect in RD is in the alpha-hydroxylation of phytanic acid; whereas in RCDP both alpha-hydroxylation of phytanic acid as well as decarboxylation of alpha-hydroxyphytanic acid are deficient.

La maladie de Refsum

Refsum's disease, firstly described almost 50 years ago by the Norvegian neurologist Sigvald Refsum, is an autosomic recessive disease affecting mostly the Scandinavians and the populations originating from Northern Europe. The disease results from a specific enzyme deficiency of the first step of phytanic acid catabolism pathway. This deficiency leads to an accumulation of this C20 fatty acid in the serum and the tissues with a preference for adipose tissue, liver and kidneys. The clinical picture includes retinitis pigmentosa, peripheral neuropathy, ataxia and elevated cerebrospinal fluid protein concentration. Other less frequent manifestations include cranial nerves deficiency, myocardiopathy, renal tubular dysfunction and ichtyosis. The diagnosis relies on serum phytanic acid measurement. The treatment consists of a phytanic-acid free diet sometimes associated with plasmapheresis. This treatment is generally effective on neuropathy but not on cranial nerves dysfunction and retinitis pigmentosa.

Complementation analysis in patients with the clinical phenotype of a generalised peroxisomal disorder.

The generalised peroxisomal disorders (GPDs) Zellweger syndrome (ZS), neonatal adrenoleucodystrophy (NALD), and infantile Refsum's disease (IRD) are autosomal recessive disorders associated with a failure to assemble mature peroxisomes. We confirmed the diagnosis of a GPD in eight ZS and four IRD patients (GPD1 to GPD12) biochemically by measuring very long chain fatty acids, plasmalogen biosynthesis, and catalase solubility in skin fibroblasts. One further patient (BOX-1) had the clinical phenotype of ZS, but biochemical investigations indicated an isolated deficiency of peroxisomal beta oxidation. To date a total of 10 complementation groups (CGs) for the GPDs and three further CGs for isolated beta oxidation deficiencies have been identified. Most GPD patients have been shown to belong to CG-1 (Baltimore classification); among the rarer groups, CG-4 and CG-8 predominate. We performed somatic cell hybridisation experiments on strains GPD-1 to GPD-12 using plasmalogen biosynthesis as a marker for correction and found that six ZS and three IRD patients, eight of whom were of UK origin, belonged to CG-1. Strain GPD-11, a patient of UK origin with an unusual biochemical phenotype, belonged to CG-8. Strains GPD-10 and GPD-12 were derived from ZS patients of Arabian and Pakistani origin and belonged to the rarer CGs 2 and 7, respectively. Furthermore, complementation analysis using beta oxidation as a marker showed that BOX-1 had an isolated deficiency of the bifunctional protein.

PRENATAL DIAGNOSIS OF PEROXISOMAL DISORDERS. † 869

Peroxisomal disorders are genetic disease caused either by a defect in peroxisome biogenesis resulting in deficiencies of multiple peroxisomal enzymes or by a deficiency of one peroxisomal enzyme. Seventeen different peroxisomal disorders are recognized nowadays, with progressive neurological deficits and early death in most. Both in peroxisome deficiency disorders(PDD) like Zellweger syndrome, neonatal Adrenoleukodystrophy (n-ALD) and infantile Refsum disease, in classic rhizomelic Chondrodysplasia punctata(RCDP) and disorders with a defect in peroxisomal beta-oxidation of fatty acids (including X-linked ALD) no effective treatment is available and early prenatal detection indicated. For PDD this is done by us by in vitro measurement of acylCoA:dihydroxyacetonephosphate acyltransferase(DHAPAT) activity and immuno(western)blotting with antisera raised against catalase, acylCoA oxidase and peroxisomal thiolase(Thio) resp. in uncultured chorionic villi(CV) homogenates. Since 1992 seventeen affected PDS fetusses were recognized by us by this procedure in sixty one at risk pregnancies in the 10th or 11th gestational week. Moreover, an additional thirteen affected PDS fetusses were found by analyzing de novo plasmalogen biosynthesis and very longchain fatty acids(VLCFA) in cultured CV-fibroblasts or amniocytes. Seven RCDP fetusses were diagnosed by the finding of abnormal immunoblots with anti-thiolase (absence of 41kDa band for mature thiolase protein) and deficient plasmalogens in CV. We also diagnosed isolated DHAPAT deficiency in a fetus by finding a deficiency of plasmalogens and DHAPAT, but normal Thio-blot in CV. Fifteen fetusses with a deficiency of one of the enzymes of peroxisomal beta-oxidation, including X-linked ALD, were diagnosed prenatally in 41 at risk pregnancies by the finding of elevated VLCFA and deficient activity of peroxisomal beta-oxidation in cultured CV-fibroblasts or amniocytes. No false positive or negative cases were found with these procedures.

Intermittent horizontal saccade failure ('ocular motor apraxia') in children.

Ocular motor apraxia (OMA) in childhood is a poorly understood condition involving a failure of horizontal saccades. OMA is thought to be rare but the literature indicates wide clinical associations. OMA is often identified by abnormal head movements, but failure of reflexive quick phases has been reported in all but a few patients. The extent of this oculomotor disorder was examined in a large group of children with diverse clinical backgrounds. The degree of quick phase failure during horizontal vestibular and optokinetic nystagmus was measured using DC electro-oculography and video in 74 affected children, aged 17 days to 14 years. All children showed an intermittent failure of nystagmic quick phases, except for total failure in one case. Other visuomotor abnormalities were common including saccadic hypometria (85%), low gain smooth pursuit (70%), neurological nystagmus (28%), strabismus (22%), and vertical abnormalities (11%). Non-ocular abnormalities were common including infantile hypotonia (61%), motor delay (77%), and speech delay (87%). There was a wide range of clinical associations including agenesis of the corpus callosum, Joubert syndrome, Dandy-Walker malformation, microcephaly, hydrocephalus, vermis hypoplasia, porencephalic cyst, megalocephaly, Krabbe leucodystrophy, Pelizaeus Merzbacher disease, infantile Gaucher disease, GM1 gangliosidosis, infantile Refsum's disease, propionic acidaemia, ataxia telangiectasia, Bardet-Biedl syndrome, vermis astrocytoma, vermis cyst, carotid fibromuscular hypoplasia, Cornelia de Lange syndrome, and microphthalmos. Perinatal and postnatal problems were found in 15% including perinatal hypoxia, meningitis, periventricular leucomalacia, athetoid cerebral palsy, perinatal septicaemia and anaemia, herpes encephalitis, and epilepsy. Only 27% were idiopathic. Quick phase failure is a constant feature of OMA, whereas abnormal head movements were detected in only about half, depending on the underlying diagnosis. This oculomotor sign is better described as an intermittent saccade failure rather than as a true apraxia. It indicates central nervous system involvement, has wide clinical associations, but it is not a diagnosis.

Studies on the degradation of [U-3H]-phytanic acid and [U-3H]-pristanic acid in cultured fibroblasts from children with peroxisomal disorders.

Up till now, errors of phytanic acid metabolism in children with peroxisomal disorders have been estimated by measuring 14CO2 formation from 1-14C-labelled phytanic acid in different systems. In the present work we have incubated both 1-14C- and U-3H-labelled phytanic acid and U-3H-labelled pristanic acid with cultured fibroblasts from healthy children as well as from children with peroxisomal disorders. In cultured fibroblasts from healthy children, [U-3H]-pristanic acid was degraded at a rate 60 times that of [U-3H]-phytanic acid, indicating that the initial degradation of phytanic acid into pristanic acid is the rate-limiting step in the overall conversion. In cultured fibroblasts from children with the Zellweger syndrome and infantile Refsum disease, the degradation of both phytanic acid and pristanic acid, was severely impaired (10-40 and 10-30 times, respectively), but the degradation of pristanic acid was still more than 20 times higher than that of phytanic acid in these disorders. In fibroblasts from a child with rhizomelic chondrodysplasia punctata the rate of degradation of U-3H- and 1-14C-labelled phytanic acid was markedly reduced whereas the rate of degradation of U-3H-labelled pristanic acid was normal. No evidence was obtained for elongation of phytanic or pristanic acid in the different fibroblastic cultures. It is concluded that both the degradation of phytanic acid and pristanic acid may be affected in peroxisomal disorders. The possibility that phytanic acidaemia in these disorders is due to product inhibition of accumulated pristanic acid seems to be excluded. The pristanic acidaemia sometimes seen is likely to be due to dietary pristanic acid rather than to de novo synthesized pristanic acid from accumulated phytanic acid.

Ketoconazole and other imidazole derivatives are potent inhibitors of peroxisomal phytanic acid α-oxidation

The imidazole antimycotics like ketoconazole, clotrimazole, bifonazole, miconazole and CO, known as powerful inhibitors of cytochrome P-450, are potent inhibitors of peroxisomal phytanic acid α-oxidation to pristanic acid suggesting the possible involvement of the cytochrome P-450 mono-oxygenase system in this oxidation. In contrast to the inhibition of the oxidation of [1- 14C]phytanic acid, [1- 14C]phytanoyl-CoA and [(2,3)- 3H]phytanic acid, these drugs and CO have no effect on the oxidation of [1- 14C]α-hydroxy phytanic acid indicating that these drugs and CO inhibit only the α-hydroxylation of phytanic acid. These studies using purified peroxisomes from liver and cultured human skin fibroblasts and Hep G2 cells clearly demonstrate that α-hydroxylation, an intermediate step in the α-oxidation of phytanic acid found to be impaired in Refsum Disease, is mediated by cytochrome P-450 containing enzyme.