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PubMed1992

Effect of phytanic acid on cultured retinal pigment epithelium: an in vitro model for Refsum's disease.

Refsum's disease (heredopathia atactica polyneuritiformis) is an autosomal recessive retinitis pigmentosa syndrome caused by the excessive deposition of phytanic acid in ocular tissues. It is thought that phytanic acid causes retinal degeneration either by interfering with vitamin A metabolism in the retinal pigment epithelium or by altering photoreceptor cell membrane structure. Efforts to elucidate the molecular mechanism of phytanic acid's retinal toxicity have been hampered by the rarity of human pathological specimens and by the inability to reproduce the disease in living animal models. In this study, an in vitro model for Refsum's disease was established by exposing cultured human and bovine retinal pigment epithelial cells to phytanic acid bound to bovine serum albumin at concentrations comparable to levels found in affected humans. Ultrastructural studies show that these cells exhibit morphological changes consistent with those observed in pathological specimens from patients with Refsum's disease. Biochemical assays of retinoid metabolism by cell membranes from control cells and from cells exposed to 200 microM phytanic acid demonstrate that the ability to esterify retinol and to isomerize all-trans retinoids to 11-cis retinoids remains intact despite the deposition of large amounts of phytanic acid. The work described here is strong evidence against the hypothesis that phytanic acid inhibits vitamin A metabolism in the retinal pigment epithelium, and it demonstrates the potential use of cultured retinal pigment epithelial cells in modeling this and other degenerative diseases of the retina.

Animals↗
PubMed1989

A case of Refsum disease with atypical clinical picture in family members.

A typical case of Refsum disease with high phytanic acid plasma levels is described. Two siblings showed some features but not the entire clinical spectrum of the disease. The unusual condition of the patient's father, a presumed heterozygotic carrier with characteristic bone abnormalities and a delayed onset retinopathy, is discussed.

Adult↗
PubMed2006

Mechanism of toxicity of the branched-chain fatty acid phytanic acid, a marker of Refsum disease, in astrocytes involves mitochondrial impairment.

Phytanic acid is a saturated branched-chain fatty acid, which is formed by bacterial degradation of chlorophyll in the intestinal tract of ruminants. The methyl group in beta-position prevents degradation of phytanic acid by the beta-oxidation pathway. Therefore, degradation of phytanic acid is initiated by alpha-oxidation in peroxisomes. The inherited peroxisomal disorder Refsum disease is characterised by accumulation of phytanic acid. Unusually high concentrations of phytanic acid can be found in the plasma of Refsum disease patients, who suffer from neurodegeneration and muscle dystrophy. Phytanic acid has been suggested to be causally involved in the clinical symptoms. To elucidate the pathogenic mechanism, we investigated the influence of phytanic acid in rat hippocampal astrocytes by monitoring the cytosolic Ca(2+) concentration, the mitochondrial membrane potential (Deltapsi(m)), the generation of reactive oxygen species as well as the cellular ATP level. In response to phytanic acid (100 microM) cytosolic Ca(2+) was quickly increased. The phytanic acid-evoked Ca(2+) response was transient and involved activation of intracellular Ca(2+) stores. In isolated rat brain mitochondria, phytanic acid dissipated Deltapsi(m) in a reversible and dose-dependent manner. Moreover, phytanic acid released cytochrome c from mitochondria. Depending on the mitochondrial activity state, phytanic acid either stimulated or inhibited the electron flux within the respiratory chain. In addition, phytanic acid induced substantial generation of reactive oxygen species in isolated mitochondria as well as in intact cells. Phytanic acid caused cell death of astrocytes within a few hours of exposure. In conclusion, we suggest that phytanic acid initiates astrocyte cell death by activating the mitochondrial route of apoptosis.

Animals↗
PubMed1998

Restoration of phytanic acid oxidation in Refsum disease fibroblasts from patients with mutations in the phytanoyl-CoA hydroxylase gene.

Refsum disease (RD) is biochemically characterized by the excessive accumulation of phytanic acid in tissues and body fluids due to deficiency of phytanoyl-CoA hydroxylase (PAHX). In this study, we screened three RD patients and identified a novel deletion (88 amino acids), and a missense mutation (Arg275Trp) in the previously reported PAHX cDNA (Jansen et al., 1997; Mihalik et al., 1997). Moreover, transfection of skin fibroblasts from two RD patients with wild-type PAHX gene restored the activity for alpha-oxidation of phytanic acid. Southern analysis on a somatic cell hybrid panel detected the PAHX gene on chromosome 10, corroborating radiation hybrid and homozygosity mapping data (Mihalik et al., 1997; Nadal et al., 1995).

Chromosome Mapping↗
PubMedDate not supplied

[Pauci-symptomatic sensory polyneuropathy in Refsum's disease].

Refsum's disease is an autosomal recessive disease caused by defective alpha-oxidation of phytanic acid. The usual clinical presentation is the association of retinitis pigmentosa, ataxia and chronic severe sensorimotor polyneuropathy. A case of mild purely sensory neuropathy in a 40-year-old patient associated to high CSF protein level led to the diagnosis of Refsum's disease. The paucity of sensory symptoms and signs of neuropathy contrasted with severe reduction of motor and sensory nerve conduction velocities and markedly signs of sensory neuropathy observed in the nerve biopsy. Typical ring-scotomas, retinitis pigmentosa, anosmia, deafness, and high plasma phytanic acid level were present in extensive examination. There was no other case in the family.

Adult↗
PubMed1992

Infantile refsum disease: gastrointestinal presentation of a peroxisomal disorder.

This article describes two siblings with infantile Refsum disease (IRD) whose initial presentation was that of malabsorption and mimicked a-beta- or homozygous hypo-beta-lipoproteinemia. Failure to recognize IRD in the first-born child precluded proper genetic counseling and prenatal diagnosis in subsequent pregnancies and also caused considerable delay in diagnosing IRD in the second child. The clinical heterogeneity of peroxisomal disorders constitutes a diagnostic challenge, which demands a high degree of awareness from the part of the clinician. This is particularly the case with IRD, where protracted diarrhea with low serum cholesterol levels appears to be a frequently occurring initial feature during the 1st months of life.

Abetalipoproteinemia↗
PubMed1991

Long-term plasma exchange in a case of Refsum's disease.

Refsum's disease (Heredopathia atactica polyneuritiformis) is caused by accumulation of phytanic acid in all body tissues due to an inherited failure of alpha-oxidation of branched chain fatty acids. Plasmapheresis has been reported to be beneficial by removal of phytanic acid from the blood. We describe a patient with Refsum's disease in whom long-term plasmapheresis did not improve clinical, biochemical or electrophysiological parameters.

Adult↗
PubMed2001

Structure-function analysis of phytanoyl-CoA 2-hydroxylase mutations causing Refsum's disease.

Refsum's disease is a neurological syndrome characterized by adult-onset retinitis pigmentosa, anosmia, sensory neuropathy and phytanic acidaemia. Many cases are caused by mutations in peroxisomal oxygenase phytanoyl-CoA 2-hydroxylase (PAHX) which catalyses the initial alpha-oxidation step in the degradation of phytanic acid. Both pro and mature forms of recombinant PAHX were produced in Escherichia coli, highly purified, and shown to have a requirement for iron(II) as a co-factor and 2-oxoglutarate as a co-substrate. Sequence analysis in the light of crystallographic data for other members of the 2-oxoglutarate-dependent oxygenase super-family led to secondary structural predictions for PAHX, which were tested by site-directed mutagenesis. The H175A and D177A mutants did not catalyse hydroxylation of phytanoyl-CoA, consistent with their assigned role as iron(II) binding ligands. The clinically observed P29S, Q176K, G204S, N269H, R275Q and R275W mutants were assayed for both 2-oxoglutarate and phytanoyl-CoA oxidation. The P29S mutant was fully active, implying that the mutation resulted in defective targeting of the protein to peroxisomes. Mutation of Arg-275 resulted in impaired 2-oxoglutarate binding. The Q176K, G204S and N269H mutations caused partial uncoupling of 2-oxoglutarate conversion from phytanoyl-CoA oxidation. The results demonstrate that the diagnosis of Refsum's disease should not solely rely upon PAHX assays for 2-oxoglutarate or phytanoyl-CoA oxidation.

Amino Acid Sequence↗
PubMed1986

Hepatic peroxisomes are deficient in infantile refsum disease: a cytochemical study of 4 cases.

We examined liver biopsies from 4 patients with the infantile form of Refsum disease. No peroxisomes were visualized by light microscopy after cytochemical staining for catalase, a marker enzyme for this organelle. Absence of peroxisomes was confirmed by electron microscopy in 3 patients; in the 4th patient we observed organelles of peculiar size and structure and with minimal catalase activity. Light microscopy also showed birefringent macrophages containing P.A.S.-positive material; they were abundant in the 3 older children, and rare in the youngest (8 months). Peroxisomes and birefringent macrophages were absent in 2 patients with the cerebrohepatorenal syndrome of Zellweger. The simultaneous presence of these unique light microscopical characteristics may be of diagnostic value.

Birefringence↗
PubMed2004

Changes underlying arrhythmia in the transgenic heart overexpressing Refsum disease gene-associated protein.

Previously, we identified a novel neuron-specific protein (PAHX-AP1) that binds to Refsum disease gene product (PAHX), and we developed transgenic (TG) mice that overexpress heart-targeted PAHX-AP1. These mice have atrial tachycardia and increased susceptibility to aconitine-induced arrhythmia. This study was undertaken to elucidate the possible changes in ion channels underlying the susceptibility to arrhythmia in these mice. RT-PCR analyses revealed that the cardiac expression of adrenergic beta(1)-receptor (ADRB1) was markedly lower, whereas voltage-gated potassium channel expression (Kv2.1) was higher in PAHX-AP1 TG mice compared with non-TG mice. However, the expression of voltage-sensitive sodium and calcium channels, and muscarinic receptor was not significantly different. Propranolol pretreatment, a non-specific beta-adrenoceptor antagonist, blocked aconitine-induced arrhythmia in non-TG mice, but not in PAHX-AP1 TG mice. Our results indicate that, in the PAHX-AP1 TG heart, the modulation of voltage-gated potassium channel and ADRB1 expression seem to be important in the electrophysiological changes associated with altered ion channel functions, but ADRB1 is not involved in the greater susceptibility to aconitine-induced arrhythmia.

Aconitine↗
PubMedDate not supplied

[Refsum's disease].

Refsum's disease although rare is of great interest for it may benefit at least partially from treatment. Its clinical diagnosis depends on the association of pigmented retinitis, polyneuritis and cerebellar syndrome. It is confirmed beyond doubt by the increased C.S.F. protein and phytanemia. A full family history is necessary for it is possible to detect heterozygous carriers of the defect by enzyme studies on fibroblast cultures.

Adolescent↗
PubMed2000

Human phytanoyl-CoA hydroxylase: resolution of the gene structure and the molecular basis of Refsum's disease.

Refsum's disease (RD) is an inherited neurological syndrome biochemically characterized by the accumulation of phytanic acid in plasma and tissues. Patients with RD are unable to degrade phytanic acid due to a deficient activity of phytanoyl-CoA hydroxyl-ase (PhyH), a peroxisomal enzyme catalysing the first step of phytanic acid alpha-oxidation. To enable mutation analysis of RD at the genome level, we have elucidated the genomic organization of the PHYH gene. The gene is approximately 21 kb and contains nine exons and eight introns. Mutation analysis of PHYH cDNA from 22 patients with RD revealed 14 different missense mutations, a 3 bp insertion, and a 1 bp deletion, which were all confirmed at the genome level. A 111 bp deletion identified in the PHYH cDNA of several patients with RD was due to either one of two different mutations in the same splice acceptor site, which result in skipping of exon 3. Six mutations, including a large in-frame deletion and five missense mutations, were expressed in the yeast Saccharomyces cerevisiae to study their effect on PhyH activity. The results showed that all these mutations lead to an enzymatically inactive PhyH protein.

Amino Acid Substitution↗
PubMed1983

Location of double bonds in two unsaturated forms of phytanic acid from Refsum disease as determined by mass spectrometry.

A monounsaturated and a triunsaturated form of phytanic acid (3,7,11,15-tetramethylhexacosanoate) were isolated from plasma lipids of a patient with Refsum disease. Both were converted to their methyl esters, oxidized to polyhydroxy acids by treatment with OsO4 and converted to their vicinal trimethylsilyl ethers. These derivatives were analyzed by gas chromatography-mass spectrometry using both electron impact ionization (at 21 and 70 eV) and chemical ionization conditions to obtain clear evidence to establish the structure of the monounsaturated form of phytanic acid as 3,7,11,15-tetramethylhexadec-15-monoenoic acid and that of the triunsaturated form of phytanic acid as 3,7,11,15-tetramethylhexadec-6,10,14-trienoic acid. The possible metabolic and dietary sources for these novel fatty acids are discussed.

Chemical Phenomena↗
PubMed2004

Omega-hydroxylation of phytanic acid in rat liver microsomes: implications for Refsum disease.

The 3-methyl-branched fatty acid phytanic acid is degraded by the peroxisomal alpha-oxidation route because the 3-methyl group blocks beta-oxidation. In adult Refsum disease (ARD), peroxisomal alpha-oxidation is defective, which is caused by mutations in the gene coding for phytanoyl-CoA hydroxylase in the majority of ARD patients. As a consequence, phytanic acid accumulates in tissues and body fluids. This study focuses on an alternative route of phytanic acid degradation, omega-oxidation. The first step in omega-oxidation is hydroxylation at the omega-end of the fatty acid, catalyzed by a member of the cytochrome P450 multienzyme family. To study this first step, the formation of hydroxylated intermediates was studied in rat liver microsomes incubated with phytanic acid and NADPH. Two hydroxylated metabolites of phytanic acid were formed, omega- and (omega-1)-hydroxyphytanic acid (ratio of formation, 5:1). The formation of omega-hydroxyphytanic acid was NADPH dependent and inhibited by imidazole derivatives. These results indicate that phytanic acid undergoes omega-hydroxylation in rat liver microsomes and that an isoform of cytochrome P450 catalyzes the first step of phytanic acid omega-oxidation.

Animals↗
PubMed1999

Refsum disease diagnostic marker phytanic acid alters the physical state of membrane proteins of liver mitochondria.

Phytanic acid (3,7,11,15-tetramethylhexadecanoic acid), a branched chain fatty acid accumulating in Refsum disease to high levels throughout the body, induces uncoupling of rat liver mitochondria similar to non-branched fatty acids (e.g. palmitic acid), but the contribution of the ADP/ATP carrier or the aspartate/glutamate carrier in phytanic acid-induced uncoupling is of minor importance. Possible deleterious effects of phytanic acid on membrane-linked energy coupling processes were studied by ESR spectroscopy using rat liver mitochondria and a membrane preparation labeled with the lipid-specific spin probe 5-doxylstearic acid (5-DSA) or the protein-specific spin probe MAL-TEMPO (4-maleimido-2,2,6, 6-tetramethyl-piperidine-1-oxyl). The effects of phytanic acid on phospholipid molecular dynamics and on the physical state of membrane proteins were quantified by estimation of the order parameter or the ratio of the amplitudes of the weakly to strongly immobilized MAL-TEMPO binding sites (W/S ratio), respectively. It was found, that phytanic acid (1) increased the mobility of phospholipid molecules (indicated by a decrease in the order parameter) and (2) altered the conformational state and/or the segmental mobility of membrane proteins (indicated by a drastic decrease in the W/S ratio). Unsaturated fatty acids with multiple cis-double bonds (e.g. linolenic or arachidonic acid), but not non-branched FFA (ranging from chain length C10:0 to C18:0), also decrease the W/S ratio. It is hypothesized that the interaction of phytanic acid with transmembrane proteins might stimulate the proton permeability through the mitochondrial inner membrane according to a mechanism, different to a protein-supported fatty acid cycling.

Biological Transport↗
PubMed1996

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.

Biological Transport↗
PubMed1979

Skeletal changes in Refsum's disease.

Refsum's disease is a rare inherited disease of lipid metabolism. The cardinal diagnostic features include polyneuritis, cerebellar ataxia, an atypical pigmentosa and a high CSF protein. The disorders is accompanied by the accumulation in the tissues, especially the liver and kidneys, of the lipid 'phytanic acid'. The disease is due to the absence of the enzyme phytanic acid alpha-hydroxylase which catalyses the conversion of phytanic acid to alpha-hydroxy phytanic acid the initial step in its further metabolism. In his original monograph Refsum (1945) documented a number of skeletal abnormalities and the full spectrum of changes that occur has become clear though the accumulating subsequent reports. This paper documents the osseous changes in three members with the disease in a single family. These include epiphyseal dysplasia, especially pronounced in the knees, and shortening and deformity of many of the tubular bones in the hands and feet.

Adult↗