Refsum's disease: nature of the enzyme defect

Phytyl fatty acid esters in vegetables pose a risk for patients suffering from Refsum's disease

Patients suffering from Refsum’s disease show mutations in the enzyme necessary for the degradation of phytanic acid. Accumulation of this tetramethyl-branched fatty acid in inner organs leads to severe neurological and cardiac dysfunctions which can even result in death. Thus, patients with Refsum’s disease have to follow a specific diet resigning foods with high levels of phytanic acid and trans-phytol like products from ruminant animals with a tolerable daily intake (TDI) of ≤ 10 mg/d. We recently reported the occurrence of phytyl fatty acid esters (PFAE, trans-phytol esterified with a fatty acid) in bell pepper with trans-phytol amounts of up to 5.4 mg/100 g fresh weight (FW). In this study we carried out in vitro-digestion experiments of PFAE with artificial digestion fluids. Our results demonstrate that PFAE actually are a source for bioavailable trans-phytol and thus add to the TDI. Eating only one portion of bell pepper (∼150 g) could therefore lead to exploitation of the TDI of up to 81%. Analysis of additional vegetable matrices showed that also rocket salad with up to 4.2 mg/100 g FW trans-phytol bound in PFAE represents a risk-relevant food for patients with Refsum’s disease and should therefore be taken into account.

Analytical authentication of organic products: an overview of markers

Consumers' interest in organic foods is increasing and so is the need for robust analytical tools for their authentication. This review focuses on the most promising biomarkers/analytical approaches that are available for the authentication of organic produce. Food products have been subdivided into two groups: foods of plant origin (crops) and foods of animal origin (meat, milk and dairy products, eggs and fish). For each food category the most suitable biomarkers are presented and their potential for authentication is discussed. In the light of current knowledge, it is unlikely that the authentication of organic food products can be attained by the measurement of a single marker. Analytical approaches based on the measurement of multiple markers and/or complex chemical or physical profiles/fingerprints supported by multivariate statistical analysis seem considerably more promising in this respect. For the development of robust classification models, well-designed experimental studies must be performed that rely on data sets that are both well balanced and of sufficient size to ensure that all relevant sources of variation for the target biomarkers are included in the reference database.

Chance and serendipity in science: two examples from my own career

The usual scientific paper follows a rather narrowly (but not ever rigidly) defined pattern. Both the author and the journal like to see a linear logical presentation of a "story." Seldom does the paper give the reader the "backstory." Where did the idea come from in the first place? How many false leads led down blind alleys? What happened by chance and what by logical planning? Was there an element of serendipity involved? Perhaps as we enter the paperless era and do not have to count words quite so religiously, it may be possible to encourage a more freewheeling scientific paper, but for now, we have to rely on the historians of science and/or those who "tell all" about their own research. "Reflections" seems an appropriate space for the latter. I have chosen two scenarios from my own career in which happy accidents played important roles but, unhappily, received little recognition in my published papers.

The isolation and identification of 4,8,12-trimethyltridecanoic acid from butterfat

The isoprenoid fatty acid 4,8,12-trimethyltridecanoic acid has been isolated from butterfat and identified. This acid was found to be a DD diastereoisomer, and was thought to have been derived from the phytol moiety of chlorophyll. It was estimated that in the sample of butterfat investigated, 4,8,12-trimethyltridecanoic acid constituted about 0·005% of the total weight of fatty acids.

Dr Brian Gibberd (1931-2006): a pioneering clinician in Refsum's disease

Branched-chain fatty acids are common components of the human diet (phytanic acid) or are produced endogenously (bile acids), and are also used as medicines (ibuprofen). Owing to their branched-chain structure, they are metabolized in peroxisomes. In the case of phytanic acid, the presence of a 3-methyl group prevents beta-oxidation, and instead it undergoes one round of alpha-oxidation to allow further metabolism. Defects in this process give rise to neurological diseases and cancer. Dr Brian F. Gibberd was one of the first U.K. physicians to recognize the importance of these peroxisomal metabolic pathways in clinical medicine, and pioneered their study. This obituary recognizes his many achievements in neurology and especially in the treatment of peroxisomal disorders. The following four papers from this mini-symposium entitled 'Advances in peroxisomal alpha-, beta- and omega-oxidation' describe work done in this area as part of a collaborative study in which Dr Gibberd played a key role. This work was presented as part of the Cardiovascular Bioscience focused topic at the Life Sciences 2007 conference, and this mini-symposium was dedicated to Dr Gibberd and his important contributions to this field.

Peroxisomal disorders affecting phytanic acid α-oxidation: a review

Peroxisomes are involved in the synthesis and degradation of complex fatty acids. They contain enzymes involved in the α-, β- and ω-oxidation pathways for fatty acids. Investigation of these pathways and the diseases associated with mutations in enzymes involved in the degradation of phytanic acid have led to the clarification of the pathophysiology of Refsum's disease, rhizomelic chondrodysplasia and AMACR (α-methylacyl-CoA racemase) deficiency. This has highlighted the role of an Fe(II)- and 2-oxoglutarate-dependent oxygenases [PhyH (phytanoyl-CoA 2-hydroxylase), also known as PAHX], thiamin-dependent lyases (phytanoyl-CoA lyase) and CYP (cytochrome P450) family 4A in fatty acid metabolism. The differential regulation and biology of these pathways is suggesting novel ways to treat the neuro-ophthalmological sequelae of Refsum's disease. More recently, the discovery that AMACR and other peroxisomal β-oxidation pathway enzymes are highly expressed in prostate and renal cell cancers has prompted active investigation into the role of these oxidation pathways and the peroxisome in the progression of obesity- and insulin resistance-related cancers.

The chemical biology of branched-chain lipid metabolism

Mammalian metabolism of some lipids including 3-methyl and 2-methyl branched-chain fatty acids occurs within peroxisomes. Such lipids, including phytanic and pristanic acids, are commonly found within the human diet and may be derived from chlorophyll in plant extracts. Due to the presence of a methyl group at its beta-carbon, the well-characterised beta-oxidation pathway cannot degrade phytanic acid. Instead its alpha-methylene group is oxidatively excised to give pristanic acid, which can be metabolised by the beta-oxidation pathway. Many defects in the alpha-oxidation pathway result in an accumulation of phytanic acid, leading to neurological distress, deterioration of vision, deafness, loss of coordination and eventual death. Details of the alpha-oxidation pathway have only recently been elucidated, and considerable progress has been made in understanding the detailed enzymology of one of the oxidative steps within this pathway. This review summarises these recent advances and considers the roles and likely mechanisms of the enzymes within the alpha-oxidation pathway.

Metabolism of phytanic acid and 3-methyl-adipic acid excretion in patients with adult Refsum disease

Adult Refsum disease (ARD) is associated with defective alpha-oxidation of phytanic acid (PA). omega-Oxidation of PA to 3-methyl-adipic acid (3-MAA) occurs although its clinical significance is unclear. In a 40 day study of a new ARD patient, where the plasma half-life of PA was 22.4 days, omega-oxidation accounted for 30% initially and later all PA excretion. Plasma and adipose tissue PA and 3-MAA excretion were measured in a cross-sectional study of 11 patients. The capacity of the omega-oxidation pathway was 6.9 (2.8-19.4) mg [20.4 (8.3-57.4) micromol] PA/day. 3-MAA excretion correlated with plasma PA levels (r = 0.61; P = 0.03) but not adipose tissue PA content. omega-Oxidation during a 56 h fast was studied in five patients. 3-MAA excretion increased by 208 +/- 58% in parallel with the 158 (125-603)% rise in plasma PA. Plasma PA doubled every 29 h, while 3-MAA excretion followed second-order kinetics. Acute sequelae of ARD were noted in three patients (60%) after fasting. The omega-oxidation pathway can metabolise PA ingested by patients with ARD, but this activity is dependent on plasma PA concentration. omega-Oxidation forms a functional reserve capacity that enables patients with ARD undergoing acute stress to cope with limited increases in plasma PA levels.

Scavenger receptor class B type I is expressed in cultured keratinocytes and epidermis. Regulation in response to changes in cholesterol homeostasis and barrier requirements

Cholesterol is a key lipid in the stratum corneum, where it is critical for permeability barrier homeostasis. The epidermis is an active site of cholesterol synthesis, but inhibition of epidermal cholesterol synthesis with topically applied statins only modestly affects epidermal permeability barrier function, suggesting a possible compensatory role for extraepidermal cholesterol. Scavenger receptor class B type I (SR-BI) is a recently described cell surface receptor for high density lipoproteins (HDL) that mediates the selective uptake of cholesterol esters from circulating HDL. In the present study, we demonstrate that SR-BI is present in cultured human keratinocytes and that calcium-induced differentiation markedly decreases SR-BI levels. Additionally, the cell association of [(3)H]cholesterol-labeled HDL decreased in differentiated versus undifferentiated keratinocytes. Furthermore, the inhibition of cholesterol synthesis with simvastatin resulted in a 3-4-fold increase in both SR-BI mRNA and protein levels, whereas conversely, addition of 25-hydroxycholesterol suppressed SR-BI levels by approximately 50%. SR-BI mRNA is also expressed in murine epidermis, increasing by 50% in parallel with cholesterol requirements following acute barrier disruption. Because the increase is completely blocked by occlusion with a vapor-impermeable membrane, changes in epidermal SR-BI expression are regulated specifically by barrier requirements. Lastly, using immunofluorescence we demonstrated that SR-BI is present in human epidermis predominantly in the basal layer and increases following barrier disruption. In summary, the present study demonstrates first that SR-BI is expressed in keratinocytes and regulated by cellular cholesterol requirements, suggesting that it plays a role in keratinocyte cholesterol homeostasis. Second, the increase in SR-BI following barrier disruption suggests that SR-BI expression increases to facilitate cholesterol uptake leading to barrier restoration.

BMIPP-design and development

In the early 1980s a major obstacle for myocardial SPECT using iodine-123-labeled fatty acids and imaging technology available at that time was the rapid metabolism and myocardial washout of activity. Development of the 15-(p-iodophenyl)-3-(R,S)-methylpentadecanoic acid (BMIPP) fatty acid analogue was based on the established effects of methyl-branching in delineating the enzymatic aberration in Refum's disease and our early studies with the tellurium (Te)-substituted fatty acid analogues. Extensive animal studies with the Te-fatty acids demonstrated that this major structural alteration did not affect initial myocardial extraction, but could successfully inhibit subsequent metabolism and significantly delay washout. Tracer kinetic evaluation and metabolic studies on experimental animals and Langendorff-perfused rat hearts clearly demonstrated that introduction of methyl-branching is an effective approach which alters tracer kinetics by delaying myocardial washout of radioiodinated fatty acids by increasing myocardial retention. Although irreversible retention of iodine-123 BMIPP is not observed, subsequent extensive human studies have clearly substantiated the delayed myocardial washout of BMIPP in comparison with the p-IPPA straight chain analogue. Although contemporary SPECT capabilities allow much more rapid acquisition periods, the delayed washout is still a practical benefit in relation to the use of BMIPP. Most important, the unexpected mis-match which has been widely observed between perfusion tracer distribution and the regional BMIPP distribution (i.e. BMIPP < flow tracer) has been linked to the identification of jeopardized, but viable myocardial regions. In this paper the development of BMIPP is discussed and the results of recent studies focusing on evaluating the effects of the absolute configuration of the branched methyl group using the 3(R)-BMIPP and 3(S)-BMIPP are described.

Phytanic acid must be activated to phytanoyl-CoA prior to its alpha-oxidation in rat liver peroxisomes

alpha-Oxidation of the branched-chain fatty acid, phytanic acid, is defective in patients with Refsum's disease, the disorders of peroxisome biogenesis (e.g., Zellweger syndrome), and in rhizomelic chondrodysplasia punctata. 3H-Release from [2,3-3H]phytanic acid, which is impaired in cultured skin fibroblasts from these patients, was investigated in rat liver peroxisomes. Cofactors necessary for optimal 3H-release, ATP, Mg2+, and coenzyme A, were also necessary for optimal acyl-CoA synthetase activity, suggesting that the substrate for 3H-release might be phytanoyl-CoA. 5,8,11,14-Eicosatetraynoic acid (ETYA), an inhibitor of long-chain acyl-CoA synthetase activity, blocked phytanoyl-CoA synthesis as well as 3H-release from [2,3-3H]phytanic acid in a dose-dependent manner. However, this inhibitor had little effect on 3H-release from [2,3-3H]phytanoyl-CoA. Tetradecylglycidic acid (TDGA) inhibited 3H-release from [2,3-3H]phytanic acid in peroxisomal but not in mitochondrial fractions from rat liver. This agent inhibited 3H-release from [2,3-3H]phytanic acid and [2,3-3H]phytanoyl-CoA equally. In contrast to ETYA, which appeared to decrease 3H-release as a consequence of synthetase inhibition, TDGA appeared to act directly on the enzyme catalyzing 3H-release. This enzyme was partially purified from rat liver. The purified enzyme, which did not possess phytanoyl-CoA synthetase activity, catalyzed tritium release from [2,3-3H]phytanoyl-CoA. This enzyme catalyzed 3H-release from [2,3-3H]phytanic acid only if a source of phytanoyl-CoA synthetase was present. We conclude that in rat liver peroxisomes, phytanic acid must be activated to its coenzyme A derivative prior to subsequent alpha-oxidation.

Distribution of 3-hydroxy iC17:0 in subgingival plaque and gingival tissue samples: relationship to adult periodontitis

Gram-negative organisms incorporate hydroxy fatty acids into the lipid A moiety of lipopolysaccharide (LPS), and in the case of some members of the family Enterobacteriaceae, hydroxy fatty acids are incorporated exclusively into lipid A. However, a limited number of Bacteroides species have been shown to incorporate several classes of 3-hydroxy fatty acids, particularly 3-hydroxy iC17:0, into constitutive lipids as well as LPS. The present study examined the distribution of hydroxy fatty acids in two periodontal pathogens, Prevotella intermedia and Porphyromonas gingivalis, by employing a phospholipid extraction procedure (E. G. Bligh and W. J. Dyer, Can. J. Biochem. Physiol. 37:911-917, 1959) which partitioned constitutive lipids into the organic solvent phase and LPS into the aqueous phase. The distribution of hydroxy fatty acids within organic solvent and aqueous extracts of these bacterial species was then compared with the distribution in subgingival plaque samples isolated from either gingivitis or severe periodontitis sites as well as the distribution in gingival tissue samples. The organic solvent and aqueous extracts were hydrolyzed under strong alkaline conditions, and the free fatty acids were treated to form pentafluorobenzyl-ester, trimethylsilyl-ether derivatives. Hydroxy fatty acid levels were quantified by using gas chromatography-negative-ion chemical ionization-mass spectrometry. By using this approach, the mean values of the 3-hydroxy iC17:0 recovered within organic solvent extracts of P. gingivalis strains ranged from 56 to 63% of total 3-hydroxy iC17:0. Substantially less 3-hydroxy iC17:0 (< 5%) was recovered in organic solvent extracts of P. intermedia. By comparison, 75% of the 3-hydroxy iC17:0 in periodontitis subgingival plaque samples was recovered in organic solvent extracts, while only 43% of the 3-hydroxy iC17:0 in gingivitis plaque samples from the same patients was recovered in organic solvent extracts. However, 3-hydroxy iC17:0 was recovered essentially only in organic solvent extracts of both healthy or mildly inflamed and periodontitis gingival tissue samples. The preferential recovery of 3-hydroxy iC17:0 in tissue lipids indicates that gingival tissues do not harbor significant levels of subgingival plaque organisms which contain 3-hydroxy iC17:0. Furthermore, these results indicate that LPS from these organisms is not prevalent in gingival tissues. Finally, these results indicate either selective penetration of certain bacterial lipids into gingival tissues or that 3-hydroxy iC17:0 is metabolically transferred from bacterial lipids into gingival tissue lipids.

Intraorganellar localization of CoASH-independent phytanic acid oxidation in human liver peroxisomes

In human tissues phytanic acid is alpha-oxidized to pristanic acid in peroxisomes. Studies of the intraorganellar site of alpha-oxidation of [1-14C]phytanic acid to pristanic acid in peroxisomes isolated from human liver demonstrate that phytanoyl-CoA ligase is present in the peroxisomal membrane and that the enzyme system for alpha-oxidation of phytanic acid to pristanic acid is in the peroxisomal matrix. In contrast to the beta-oxidation system for fatty acids, the substrate for alpha-oxidation is free phytanic acid. The studies described in this manuscript report a novel fatty acid oxidation system where the substrate for the enzyme system is free fatty acid; however, phytanoyl-CoA ligase regulates the alpha-oxidation of phytanic acid at the organellar (peroxisomal) level.

Identification of phytanoyl-CoA ligase as a distinct acyl-CoA ligase in peroxisomes from cultured human skin fibroblasts

Phytanic acid accumulates in excessive amounts in Refsum disease, a rare neurological disorder, due to a defect in its alpha-oxidation enzyme system in peroxisomes. The activation of phytanic acid to phytanoyl-CoA by phytanoyl-CoA ligase is a prerequisite for its alpha-oxidation. The studies described in this manuscript report that phytanoyl-CoA ligase in peroxisomes is an enzyme distinct from the previously reported acyl-CoA ligases.

Studies on phytanic acid alpha-oxidation in rat liver and cultured human skin fibroblasts

We have studied the alpha-oxidation of phytanic acid in rat liver and human skin fibroblasts in order to try to resolve the controversial issue of the subcellular site of alpha-oxidation of phytanic acid. The results show that isolated mitochondria are able to alpha-oxidize phytanic acid whereas isolated peroxisomes show no phytanic acid alpha-oxidation activity. Intact hepatocytes were found to alpha-oxidize phytanic acid at a rate which is more than 20-fold higher than the activity found in postnuclear supernatant fractions incubated under optimal conditions. The alpha-oxidation of phytanic acid was found to be sensitive to inhibitors of the respiratory chain and an uncoupler of oxidative phosphorylation. Furthermore, the alpha-oxidation of phytanic acid was found to be deficient in cultured human skin fibroblasts with an inherited deficiency of cytochrome c oxidase and in fibroblasts with a deficiency of functional peroxisomes. We conclude that mitochondria are indispensable for phytanic acid alpha-oxidation. Furthermore, we propose that one (or more) of the partial reactions in phytanic acid alpha-oxidation proceeds in peroxisomes leading to the concept that phytanic acid oxidation in the intact cell requires the participation of both mitochondria and peroxisomes.

Phytanic acid alpha-oxidation in human cultured skin fibroblasts

We studied the oxidation of [1-14C]phytanic acid, 3-methyl substituted fatty acid, to pristanic acid and 14CO2 in human skin fibroblasts. The specific activity for alpha-oxidation of phytanic acid in peroxisomes was 29- and 124-fold higher than mitochondria and endoplasmic reticulum. This finding demonstrates for the first time the presence of fatty acid alpha-oxidation enzyme system in peroxisomes.

Ultrastructure and immunocytochemistry of hepatic peroxisomes in rhizomelic chondrodysplasia punctata

Peroxisomes were studied in the liver of two rhizomelic chondrodysplasia punctata patients using electron microscopy and catalase cytochemistry. Immunoelectron microscopy was carried out on the liver of one of these patients using antibodies to catalase, acyl-CoA oxidase, bifunctional protein, 3-ketoacyl-CoA thiolase and a 68 kDa peroxisomal membrane protein, in conjunction with protein-A colloidal gold. Moderately to markedly enlarged, flocculent peroxisomes were found in both patients. In one patient they were very heterogeneous with regard to the number per hepatocyte. The peroxisomes had very low levels of catalase as indicated by cytochemistry and immunocytochemistry. The three beta-oxidation enzymes were localised normally within the peroxisomes. The 68 kDa membrane protein was localised to the peroxisomal membranes. Some extra membrane loops were also identified using this antibody.

The regulation and role of epidermal lipid synthesis

One of the key functions of the epidermis is to form a barrier between the organism and the outside world. As shown in Fig. 3, disruptions of the barrier result in a cascade of events that ultimately leads to barrier repair. The initial signal that initiates this repair response is unknown. The exocytosis of preformed lipid-enriched lamellar bodies is the first step in this response, which is followed by an increase in lipid synthesis in the epidermis. Our studies demonstrate that this increase in epidermal lipid synthesis is required for the synthesis of new lamellar bodies and repair of the barrier. Inhibition of epidermal lipid synthesis by artificial membranes or drugs impairs barrier recovery by preventing the reformation of lamellar bodies and the continued secretion of lipid. Whether the stimulation of lipid synthesis is primarily regulated by disturbances in barrier function or secondarily by decreases in the lipid content of the cells due to the utilization of lipid for the formation of lamellar bodies is unknown. Additionally, the precise mechanisms by which lipid synthesis is increased (enzyme activation, transcriptional regulation, etc.) remain to be elucidated. The secretion of lipid-containing lamellar bodies results in the reaccumulation of lipid in the intercellular spaces of the stratum corneum and the recovery of normal barrier function. Epidermal lipid synthesis also is probably required to provide lipid for new cell membrane formation to allow for the increase in epidermal cell proliferation, which is stimulated following barrier disruption. Additionally, epidermal lipid synthesis may provide regulatory molecules or crucial substrates that are required for DNA synthesis. Thus, epidermal lipid synthesis plays a key role in the major biological functions of the epidermis, the cutaneous permeability barrier, and cell proliferation.

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.

Metabolism of methyl-branched iodo palmitic acids in cultured hepatocytes

The metabolic fate of methyl-branched iodo fatty acids was studied in primary culture of rat hepatocytes. We compared 16-iodo-2-R,S-methyl palmitic acid (2-Me), which can be beta oxidized, with 16-iodo-3-R,S-methyl palmitic acid (3-Me) which can be beta oxidized only after an initial alpha oxydation and with 16-iodo-2,2-dimethyl palmitic acid (2,2-Me2) and 16-iodo-3,3-dimethyl palmitic acid (3,3-Me2) which cannot be beta oxidized at all. The normal fate of natural fatty acids was given by comparative experiments with [1-14C] palmitic acid. Monomethyl-branched iodo fatty acids were taken up in the same range as palmitic acid but more than dimethyl-branched iodo fatty acids. After a 15-h incubation, acido-soluble products (ASP) accounted for 75% of the radioactivity taken up as 16-iodo-2-methyl palmitic acid, 50% as other methyl-branched iodo fatty acids and only 30% as palmitic acid, which indicated that all the methyl-branched iodo fatty acids underwent a strong deiodination process. Fatty acids were esterified in the following order: palmitic acid greater than 16-iodo-3-R,S-methyl palmitic acid greater than 16-iodo-2-R,S-methyl palmitic acid greater than 16-iodo-2,2-dimethyl palmitic acid greater than 16-iodo-3,3-dimethyl palmitic acid. Cultured hepatocytes, labelled for 3 h with the various fatty acids and reincubated for 12 h without fatty acid, secreted large amounts of free dimethyl-branched iodo fatty acids as compared to the monomethyl ones and palmitic acid.(ABSTRACT TRUNCATED AT 250 WORDS)

A child with Refsum's disease: successful treatment with diet and plasma exchange

A child with Refsum's disease presented with cardiac failure, marked muscle wasting, weakness and inco-ordination. Management with multiple plasma exchanges and dietary restriction of phytanic acid intake has reversed the disabling features of the disease, although levels still remain higher than target values. Low phytanic acid intake is being achieved by restriction of total fat to 10 to 12 g/day, while allowing free amounts of fruit and green vegetables.

Evaluation of the metabolism in rat hearts of two new radioiodinated 3-methyl-branched fatty acid myocardial imaging agents

The biological fate of two new radioiodinated 3-methyl-branched fatty acids has been evaluated in rat hearts following intravenous administration. Methyl-branching was introduced in [15-(p-iodophenyl)-3-R,S-methylpentadecanoic acid (BMIPP) and 15-(p-iodophenyl)-3,3-dimethylpentadecanoic acid (DMIPP) to inhibit beta-oxidation. The goals of these studies were to correlate the effects of methyl-branching on the incorporation of these agents into the various fatty acid pools and subcellular distribution profiles, and to relate these data to the myocardial retention properties. The properties of BMIPP and DMIPP were compared with the 15-(p-iodophenyl)pentadecanoic acid straight-chain analogue (IPP). Differences in the heart retention of the analogues after intravenous administration in rats correlated with differences observed in subcellular distribution patterns. The dimethyl DMIPP analogue showed the longest retention and the highest association with the mitochondrial and microsomal fractions (34%, 38%) 30 min after injection. These data are in contrast to the rapid clearance of the straight-chain IPP analogue which showed much lower relative association with the mitochondria and microsomes (18%, 15%). The distribution patterns of each analogue in the various lipid pools appeared consistent with the expected capacity of the analogues to be metabolized by beta-oxidation. In contrast to the rapid oxidation of the straight-chain IPP analogue, the 3-monomethyl BMIPP analogue appeared to undergo slower oxidation and clearance, whereas the dimethyl-branched DMIPP analogue was apparently not catabolized by the myocardium. All three analogues showed some incorporation into triglycerides. The metabolism patterns of the branched analogues reported here may provide useful information in the description of the mechanisms by which BMIPP and DMIPP are retained in rat myocardium.

Effect of 3-methyl-branching on the metabolism in rat hearts of radioiodinated iodovinyl long chain fatty acids

The metabolism of two new 3-methyl-branched iodovinyl fatty acids in rat hearts was evaluated by determining the subcellular and lipid pool distribution of these radiolabeled analogues after intravenous injection. Methyl branching had been introduced into the straight chain analogue, 19-iodo-18-nonadecenoic acid (IVN), to produce the monomethyl analogue, 19-iodo-3-(R,S)-methyl-18-nonadecenoic acid (BMIVN) and the dimethyl derivative, 19-iodo-3,3-dimethyl-18-nonadecenoic acid (DMIVN) in the hope of inhibiting beta oxidation. Since the presence of 3-methyl branching results in delayed myocardial clearance in rats, differences were sought in the lipid and subcellular distribution of these branched analogues that might correlate with the prolonged retention and reflect differences in metabolism. Hearts of rats injected intravenously with the radiolabeled fatty acids were removed and homogenized and the homogenates partitioned between the chloroform-methanol (organic) fraction and the aqueous fraction. Comparison of the distribution of radioactivity between the organic and aqueous fractions showed that most of the DMIVN and BMIVN activity was in the organic fraction with IVN activity initially divided equally between the two fractions. Identification of the lipid components of these organic fractions showed that there was slow incorporation of DMIVN into the triglyceride and polar lipid fractions with a slow loss from the free fatty acid fraction. With the straight chain IVN analogue which shows rapid washout from rat hearts, there was loss of activity from all 3 lipid components during the 60 min. The monomethyl branched BMIVN analogue demonstrated predominant storage in the polar lipid fraction with some incorporation into triglycerides.(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue distribution of phytanic acid and its analogues in a kinship with Refsum's disease

Three of six kin were identified, by high performance thin layer chromatography, capillary gas chromatography and mass spectrometry, as having phytanic acid storage disease. Phytanic acid was found in triacylglycerol and, to a lesser degree, in phosphatidylcholine and free fatty acids. An unsaturated analogue of phytanic acid was additionally identified in plasma and erythrocyte triacylglycerols. In plasma, branched chain fatty acids were primarily localized in the low density lipoprotein fraction. The concentration of plasma major fatty acids was not affected by the presence of these branched chain fatty acids. In contrast to plasma, only small amounts of phytanic acid were found in cerebrospinal fluid and biopsied sural nerve. The nerve phytanate was mainly associated with triacylglycerol in epineurial and perineurial tissues. Lack of phytanate accumulation in sural endoneurium, even in cases with severe fiber degeneration, suggests that demyelination in Refsum's disease may not be due to myelin instability resulting from the incorporation of branched chain fatty acids into peripheral nerve membrane.

Phytanic acid alpha oxidation in rat liver: studies on alpha hydroxylation

1. The alpha-hydroxylation of [1-14C]phytanic acid was investigated in the postnuclear fraction of rat liver. 2. The reaction required ATP, Mg, Fe3+ and molecular oxygen. Fe3+ could be replaced by Fe2+. 3. The hydroxylase activity was optimal at pH 7.5 in phosphate buffer. 4. The activity increased with postnuclear protein (5-13 mg or protein), increased with the substrate concentration at low substrate concentration. 5. The amount of the hydroxyacid formed increased with time up to 10 min. 6. Coenzyme A (100 microM-2.5 mM) stimulated the activity. 7. The activity was further stimulated by NADP and NADPH slightly and by FAD and FMN strongly, all at 100 microM concentration. 8. While CO inhibited the reaction, phenobarbital inducible cytochrome P-450 did not appear to play a role in this reaction.

Phytanic acid oxidase activity in cultured skin fibroblasts. Diagnostic usefulness and limitations

Patients with Refsum's disease lack the ability to degrade phytanic acid to pristanic acid and CO2. This defect is expressed in fibroblasts from the patients. An assay system for the degradation of phytanic acid in cultured skin fibroblasts is described. The assay makes it possible to single out patients with Refsum's disease from the cob-web of clinically related conditions. The sensitivity is, however, not good enough to diagnose the heterozygous state. A defect of the same pronounced degree as in Refsum's disease is also found in fibroblasts from patients with Zellweger's syndrome, neonatal adrenoleukodystrophy, and infantile Refsum's disease. The radioactive material remaining in the cells after incubation was identified as unmetabolized phytanic acid. No traces of radioactive intermediates could be found in the cells from any of the patient groups. This might indicate that the defects both in Refsum's disease and in the peroxisomal disorders are located either at the same metabolic step or at steps which are closely linked to each other.

Peroxisomes in infantile phytanic acid storage disease: a cytochemical study of skin fibroblasts

Cultured skin fibroblasts from six patients demonstrating clinical signs and biochemical characteristics of infantile phytanic acid storage disease (IPSD) were examined by electron microscopy, using cytochemical procedures for the demonstration of peroxisomal catalase activity. In four of the six fibroblast cell lines peroxisomes strongly reactive for catalase were present in numbers similar to those found in normal fibroblasts. Liver biopsy tissue from one of these patients showed no typical hepatic peroxisomes, but did show small, marginally reactive bodies. In two other IPSD fibroblast cell lines peroxisomes with appreciable cytochemical reactivity were rare or absent. It seems, therefore, that infantile phytanic acid storage disease is heterogeneous with respect to the presence of cytochemically recognizable peroxisomes, at least in the cases studied here. Furthermore, peroxisomes may be markedly affected in one cell type - liver - and yet not affected in another - skin fibroblasts - within a single individual.

Infantile Refsum's disease: biochemical findings suggesting multiple peroxisomal dysfunction

Infantile Refsum's disease was diagnosed in three male patients, presenting with facial dysmorphia, retinitis pigmentosa, neurosensory hearing loss, hepatomegaly, osteopenia and delayed growth and psychomotor development. An elevated plasma phytanic acid concentration and a deficient phytanic acid oxidase activity in fibroblasts were found with an accumulation of very long chain fatty acids in plasma and fibroblasts. There were elevated pipecolic acid levels in plasma, urine and CSF, and abnormal bile acid metabolites in plasma. Deficient activity of acylCoA: dihydroxyacetone phosphate acyl transferase was found in thrombocytes and fibroblasts of these patients as well as an impaired de novo plasmalogen biosynthesis in fibroblasts. These biochemical abnormalities, previously described in the Zellweger syndrome, suggest multiple peroxisomal dysfunction in our patients.

Patterns of Refsum's disease. Phytanic acid oxidase deficiency

Four children each exhibiting a profound deficiency of phytanic acid oxidase activity in cultured skin fibroblasts but with very different phenotypes, are described. A consistently raised plasma phytanic acid value, generally considered to be pathognomonic for Refsum's disease (phytanic acid oxidase deficiency), was observed in three of these children but not in the fourth, who also showed no evidence of accumulation of phytanic acid in liver or fat biopsies. Our data suggest that the clinical diagnosis of Refsum's disease in children is more difficult because the full spectrum of clinical features usually observed in adults with the disorder is not always present. Moreover, a failure to detect a raised plasma phytanic acid value may not necessarily indicate normal fibroblast phytanic acid oxidase activity.

The ichthyoses--pathogenesis and prenatal diagnosis: a review of recent advances

Disturbances in the process of normal cornification leading to pathologic scaling provide the pathophysiologic basis for the ichthyoses. These disturbances may result from either abnormalities in protein metabolism (keratinization) (i.e., the "bricks") or in lipid metabolism (i.e., the "mortar") (Fig. 1). The evidence linking the various ichthyoses to defects in protein or lipid metabolism have been reviewed. It is likely that future advances will lead not only to a more complete understanding of the pathogenesis of these disorders, but also will shed significant light on the normal stratum corneum functions of barrier formation and desquamation, as well as lead the way to more rational and effective therapies. In recent years, prenatal diagnosis has been successfully performed in several of the ichthyoses. It is likely that improvements in our ability to prenatally diagnose those disorders will advance hand-in-hand with further progress in unraveling their underlying causes.

Presence of plasma branched-chain fatty acids in multineuronal degeneration, hepatosplenomegaly and adrenocortical insufficiency

We have previously reported a unique disorder in two brothers with multi-system neuronal degeneration, hepatosplenomegaly and adrenocortical deficiency. The clinical features were different from Refsum's disease. Biochemical analysis suggested that a metabolic defect of the omega 6 polyenoic fatty acid pathway may be involved. In the present study, were have further identified by gas chromatography-mass spectrometry two branched-chain fatty acids, phytanate and pristanate, in these two patients' plasma. This small, but unequivocally elevated elevated amount of branched-chain fatty acids were primarily localized in the triacylglycerols of plasma low density lipoprotein. Such branched-chain fatty acids were not detected in skin, liver and sural nerve samples. These two cases may represent an alternative metabolic error to that found in Refsum's disease leading to phytanate accumulation.

Metabolic tapetoretinal degenerations

There are a number of metabolic diseases which cause tapetoretinal degeneration, suggesting that pure pigmentary retinopathy may also be metabolic in nature. On the other hand tapetoretinal degenerations may have various modes of inheritance, so we may conclude that the metabolic disorder at the basis of these diseases is not unique and that tapetoretinal degenerations are heterogenic. In this article, some 450 published reports on tapetoretinal degenerations are reviewed. Based on these reports, the clinical and ocular manifestations, laboratory and histopathological findings, inheritance patterns, and treatments of various syndromes characterized by tapetoretinal degenerations are described. It is hoped that the gathering together of this information in one source will acid in the future understanding of metabolically based eye disease.

Diagnosis of Refsum's disease using [1-14C]phytanic acid as substrate

The suitability of using [1-14C]phytanic acid as a substrate for the diagnosis of Refsum's disease has been examined. Normal fibroblasts cultured in medium containing low concentrations of foetal calf serum (0.5%) oxidised added [1-14C]phytanic acid to 14CO2 only slowly up to about 2 days; beyond this period a marked stimulation in oxidation was observed. Easily measurable conversion of the radiolabelled acid (from 1.5 to 5.0%) was obtained by numbers of cells at least one order of magnitude fewer than previously described. Fibroblasts from adult patients with Refsum's disease displayed about 5-10% of the normal mean activity. Small differences in residual activity were observed in the different cell lines. However, no obvious relationship was found between the degree of residual activity, the level of plasma phytanate, and the patient's clinical condition and history.

Renal involvement in Refsum's disease

Renal hemodynamic and tubular functions were measured in a patient with Refsum's disease before and after 12 weeks of twice-weekly plasmaphereses. Percutaneous renal biopsy was performed before initiation of plasmapheresis. These studies were performed to (1) define the nature of the renal lesions and the effects of phytanic acid accumulation on renal functions, and (2) assess the effects of lowering the plasma phytanic acid level on renal functions. The patient, a 39 year old woman, had lipiduria, glycosuria, cylindruria, minimal proteinuria and mild azotemia initially. Renal lesions consist of extensive vacuolization and mitochondrial changes of the tubular epithelial cells, vacuolization of the visceral epithelial cells of the glomeruli, and slight to moderate mesangial sclerosis. The impaired renal hemodynamic function and various tubular functions improved following plasmaphereses associated with reduction of plasma phytanic acid. Over-all clinical improvement was also evident.