A. Poulos

Sphingolipid activator protein deficiency in a 16-week-old atypical Gaucher disease patient and his fetal sibling: Biochemical signs of combined sphingolipidoses

We describe a patient who presented shortly after birth with hyperkinetic behaviour, myoclonia, respiratory insufficiency and hepatosplenomegaly. Gaucher-like storage cells were found in bone marrow. A liver biopsy showed massive lysosomal storage morphologically different to that in known lipid storage disorders. Biochemically, the patient had partial deficiencies of β-galactocerebrosidase, β-glucocerebrosidase and ceramidase in skin fibroblast extracts, but the sphingomyelinase activity was normal. Glucosyl ceramide and ceramide were elevated in liver tissue. Loading of cultured fibroblasts with radioactive sphingolipid precursors indicated a profound defect in ceramide catabolism. Immunological studies in fibroblasts showed a total absence of cross-reacting material to sphingolipid activator protein 2 (SAP-2). The patient died at 16 weeks of age. The fetus from his mothers next pregnancy was similarly affected. The possibility that the disorder results from a primary defect at the level of SAP-2 is discussed. We have named this unique disorder SAP deficiency.

Very long chain fatty acids in higher animals—A review

Fatty acids with greater than 22 carbon atoms (very long chain fatty acids, VLCFA) are present in small amounts in most animal tissues. Saturated and monoenoic VLCFA are major components of brain, while the polyenoic VLCFA occur in significant amounts in certain specialized animal tissues such at retina and spermatozoa. Biosynthesis of VLCFA occurs by carbon chain elongation of shorter chain fatty acid precursors while β-oxidation takes place, almost exclusively in peroxisomes. Mitochondria are unable to oxidize VLCFA because they lack a specific VLCFA coenzyme A synthetase, the first enzyme in the β-oxidation pathway. VLCFA accumulate in the tissues of patients with inherited abnormalities in peroxisomal assembly, and also in individuals with defects in enzymes catalyzing individual reactions along the β-oxidation pathway. It is believed that the accumulation of VLCFA in patient tissues contributes to the severe pathological changes which are a feature of these conditions. However, little is known of the role of VLCFA in normal cellular processes, and of the molecular basis for their contribution to the disease process. The present review provides an outline of the current knowledge of VLCFA including their biosynthesis, degradation, possible function and involvement in human disease.

Infantile Refsum's disease (phytanic acid storage disease): a variant of Zellweger's syndrome?

The activity of phytanic acid oxidase is low in infantile and adult Refsums disease, and in the cerebro‐hepato‐renal (Zellwegers) syndrome. The plasma of patients with the infantile but not the adult form of Refsums disease contains increased amounts of pipecolic acid and of at least two abnormal bile acids, one of which has been identified as 3α, 7α, 12α trihydroxy‐5β‐cholestan‐26‐oic acid. These changes are similar to those reported in the Zellweger syndrome and indicate that there may be similarities in the metabolic defects in Zellwegers syndrome and the infantile form of Refsums disease.

Very long chain fatty acid β-oxidation by rat liver mitochondria and peroxisomes

Abstract Crude mitochondrial fractions were isolated by differential centrifugation of rat liver homogenates. Subfractionation of these fractions on self-generating continuous Percoll gradients resulted in clearcut separation of peroxisomes from mitochondria. Hexacosanoic acid β-oxidation was present mainly in peroxisomal fractions whereas hexacosanoyl CoA oxidation was present in the mitochondrial as well as in the peroxisomal fractions. The presence of much greater hexacosanoyl CoA synthetase activity in the purified preparations of microsomes and peroxisomes compared to mitochondria, suggests that the synthesis of coenzyme A derivatives of very long chain fatty acids (VLCFA) is limited in mitochondria. We postulate that a specific VLCFA CoA synthetase may be required to effectively convert VLCFA to VLCFA CoA in the cell. This specific synthetase activity is absent from the mitochondrial membrane, but present in the peroxisomal and the microsomal membranes. We postulate that substrate specificity and the subcellular localization of the specific VLCFA CoA synthetase directs and regulates VLCFA oxidation in the cell.

Distinct long chain and very long chain fatty acyl CoA synthetases in rat liver peroxisomes and microsomes

Mitochondria, peroxisomes, and microsomes were isolated from rat liver homogenates, and stearic acid and lignoceric acid beta-oxidation, as well as stearoyl CoA synthetase and lignoceroyl CoA synthetase activities in the three organelles, were compared. Stearic acid beta-oxidation in peroxisomes was sixfold greater compared to the oxidation in mitochondria. Lignoceric acid beta-oxidation, observed only in peroxisomes, was fivefold lower compared to stearic acid beta-oxidation. Stearoyl CoA synthetase was present whereas lignoceroyl CoA synthetase was absent in mitochondria. Stearoyl CoA synthetase and lignoceroyl CoA synthetase activities were present in microsomes and peroxisomes, but the activity of stearoyl CoA synthetase was several-fold greater compared to lignoceroyl CoA synthetase in both organelles. The differing responses to detergents and phospholipids of stearoyl CoA and lignoceroyl CoA synthetase activities in microsomes as well as peroxisomes indicated that each activity was catalyzed by a separate enzyme. Differences in detergent and phospholipid response were also noted when either stearoyl CoA or lignoceroyl CoA synthetase activity in one organelle was compared with the corresponding activity in the other organelle, suggesting that the same activity in different organelles may be catalyzed by separate enzyme proteins.

Accumulation of pristanic acid (2, 6, 10, 14 tetramethylpentadecanoic acid) in the plasma of patients with generalised peroxisomal dysfunction.

The plasma of some patients with biochemical evidence of a generalised peroxisomal dysfunction (GPD) show greatly increased levels of phytanic acid as well as its α-oxidation product, pristanic acid (2, 6, 10, 14-tetramethylpentadecanoic acid). Increased amounts of 14- and 16- carbon branched chain fatty acids are also found in some of these patients. As pristanic acid is present in normal or near-normal amounts in classical Refsum disease and rhizomelic chondrodysplasia, two disorders characterised by deficiencies in phytanic acid oxidation, we speculate that its accumulation is not secondary to a defect in the α-oxidation of phytanic acid, but is indicative of a block in the peroxisomal β-oxidation of pristanic acid. The finding of phytanic acid, as well as a number of its metabolites in patients with inherited defects in peroxisomal biogenesis indicates that a number of the steps in phytanic acid degradation may be confined to peroxisomes.

Cerebro-hepato-renal (Zellweger) syndrome, adrenoleukodystrophy, and Refsum's disease: plasma changes and skin fibroblast phytanic acid oxidase

SummaryCerebro-hepato-renal (Zellweger) syndrome, adrenoleukodystrophy, and Refsums disease patients can be divided into at least five distinct groups, according to the nature of their plasma changes and their fibroblast phytanic acid oxidase activities. The biochemical changes in the plasma vary from an increase in a single metabolite or group of structurally related metabolites, such as in X-linked adrenoleukodystrophy (ALD) and classical Refsums disease, to an increase in a number of structurally distinct metabolites, as in neonatal ALD/Zellweger syndrome, and infantile Refsums disease. All patients, with the exception of those with the X-linked form of adrenoleukodystrophy are deficient in phytanic acid oxidase activity. The great similarity observed in neonatal adrenoleukodystrophy/Zellweger syndrome and infantile Refsums disease suggests that the basic biochemical lesion in each may be similar or at least closely related.

Accumulation and defective β-oxidation of very long chain fatty acids in Zellweger's syndrome, adrenoleukodystrophy and Refsum's disease variants

The accumulation of very long chain fatty acids in plasma and skin fibroblasts was measured in at least four separate inherited disease states. Both the magnitude and the nature of the fatty acid changes reflected the clinical status of individual patients. In Zellwegers syndrome, and to a lesser extent in infantile Refums disease, there was an increase in 24:0, 26:0, 26:1, and a number of even longer chain fatty acids, while in the X‐linked form of adrenoleukodystrophy these changes were less pronounced.

Pathology of hepatic peroxisomes and mitochondria in patients with peroxisomal disorders

The morphology of hepatic peroxisomes in five patients with metabolic disorders believed to be due to inherited defects of peroxisomal function or biogenesis is described. Electron microscopy and cytochemical staining for catalase were used to identify peroxisomes in two boys with infantile Refsums disease (IRD), a girl with autopsy confirmed neonatal adrenoleukodystrophy (NALD), and two boys with pseudo-Zellweger syndrome (PZS). In the patients with IRD and NALD hepatic peroxisomes were significantly reduced in size and number and contained electron dense centres. In the liver of the patients with PZS the peroxisomes were enlarged. Morphologically abnormal peroxisomes were also detected in autopsy tissue from one boy with PZS using electron microscopy. Lamellar-lipid inclusions and mitochondria with crystalline inclusions and/or abnormal cristae are also described in two patients, one with IRD, the other with NALD.

Molecular Species of Phosphatidylcholine Containing Very Long Chain Fatty Acids in Human Brain: Enrichment in X‐Linked Adrenoleukodystrophy Brain and Diseases of Peroxisome Biogenesis Brain

Abstract: Molecular species of phosphatidylcholine containing unsaturated (i.e., monoenoic and polyenoic) 32‐ to 40‐carbon (very long chain) fatty acids (VLCFA‐PC) are present in normal human brain, the fatty acid composition changing significantly with development. There is a marked increase in the concentration and a change in the polyenoic VLCFA composition of these molecular species in brains of patients with inherited defects in peroxisomal biogenesis [Zellwegers syndrome, neonatal adrenoleukodystrophy (ALD), and infantile Refsums disease]. In contrast, there is a marked increase in monoenoic VLCFA‐PC in X‐linked ALD whereas molecular species containing polyenoic VLCFA are minor components.