Animal peroxisomes (microbodies), lipid biosynthesis and the Zellweger syndrome

Peroxisome-mitochondria interplay and disease

Peroxisomes and mitochondria are ubiquitous, highly dynamic organelles with an oxidative type of metabolism in eukaryotic cells. Over the years, substantial evidence has been provided that peroxisomes and mitochondria exhibit a close functional interplay which impacts on human health and development. The so-called "peroxisome-mitochondria connection" includes metabolic cooperation in the degradation of fatty acids, a redox-sensitive relationship, an overlap in key components of the membrane fission machineries and cooperation in anti-viral signalling and defence. Furthermore, combined peroxisome-mitochondria disorders with defects in organelle division have been revealed. In this review, we present the latest progress in the emerging field of peroxisomal and mitochondrial interplay in mammals with a particular emphasis on cooperative fatty acid β-oxidation, redox interplay, organelle dynamics, cooperation in anti-viral signalling and the resulting implications for disease.

The human peroxisome in health and disease: the story of an oddity becoming a vital organelle

Since the first report by Rhodin in 1954, our knowledge on mammalian microbodies/peroxisomes has known several periods. An initial two decades period (1954-1973) has contributed to the biochemical individualisation of peroxisomes as a new class of subcellular organelles (de Duve, 1965). The corresponding research period failed to define a clear role of mammalian peroxisomes in vital functions and intermediary metabolism, explaining why feeling that peroxisomes might be in the human cell oddities has prevailed during several decades. The period standing from 1973 to nowadays has progressively removed this cell oddity view of peroxisomes by highlighting vital function and metabolic role of peroxisomes in health and disease along with genetic and metabolic regulation of peroxisomal protein content, organelle envelope formation and protein signal targeting mechanisms. Research on peroxisomes and their response to various drugs and metabolites, dietary and physiological conditions has also played a key role in the discovery of peroxisome proliferator activated receptors (PPARs) belonging to the nuclear hormone receptor superfamily and for which impact in science and medicine goes now by far beyond that of the peroxisomes.

Glyceryl-ether monooxygenase [EC 1.14.16.5]. A microsomal enzyme of ether lipid metabolism

The history, biological, and medical aspects of glyceryl ethers, as well as their chemical syntheses, biosynthesis, and their chemical and physical properties are briefly reviewed as background information for appreciating the importance of the enzyme glyceryl-ether monooxygenase, and for embarking on new studies of this enzyme. The occurrence, isolation and general properties of the microsomal, membrane-bound, glyceryl-ether monooxygenase from rat liver are described. Radiometric, nonradiometric, and coupled and direct spectrophotometric assays for this enzyme are detailed. The effects of detergents on the kinetics of this enzyme are described together with the stoichiometry and the effects of inhibitors. The structure-activity relationships of pterin cofactors and of ether lipid substrates, including their stereospecificities, have been summarized from enzyme kinetic data which are also tabulated. The mechanism of enzymic hydroxylation of glyceryl ethers and a model for the active site of glyceryl-ether monooxygenase are proposed from these apparent kinetic data. Notes on useful future studies of this monooxygenase have been made.

Changes in glycerophospholipid profile in experimental nephrotic syndrome

We investigated changes in the glycerophospholipids in kidney tissue and its various intracellular fractions in rats with nephrotic syndrome induced by puromycin aminonucleoside. The ethanolamine plasmalogen, 1-O-alk-1'-enyl-2-acyl-GPE (EP), was increased in kidney tissue obtained from the puromycin-treated animals. A similar increase was found in the mitochondria and endoplasmic reticulum (microsomes) of this tissue. These increases were not found in the liver. Since platelet-activating factor (PAF) is known to be produced in increased amounts in inflammatory disorders, it is suggested that the higher plasmalogen found in rat kidneys during experimental nephrotic syndrome might be derived from increased levels of this autacoid. The increase in PAF may also result in the elevation of plasma PAF-acetylhydrolase (AH) activity observed in these animals.

Ether lipid synthesis: purification and identification of alkyl dihydroxyacetone phosphate synthase from guinea-pig liver

Alkyl-dihydroxyacetone phosphate synthase, the second enzyme involved in ether phospholipid biosynthesis from dihydroxyacetone phosphate and responsible for glycero-ether bond formation, has been purified from guinea-pig liver. Alkyl-dihydroxyacetone phosphate synthase was solubilized from a membrane fraction prepared from an enriched peroxisome fraction with Triton X-100 and potassium chloride. The solubilized enzyme was further purified by chromatography on QAE-Sephadex, Matrex Red, Phosphocellulose and Concanavalin A. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis alkyl-dihydroxyacetone phosphate synthase appears as a 65 kDa band. Chromatofocusing revealed an isoelectric point of pH 5.9 for the enzyme. The pH optimum of alkyl-dihydroxyacetone phosphate synthase was found to be between pH 7 and 8 in a 50 mM potassium phosphate buffer. The specific activity of the enzyme was estimated to be at least 350 nmol.min-1.mg-1, corresponding to a purification of at least 13,000-fold.

The peroxisome and the eye

Several childhood multisystem disorders with prominent ophthalmological manifestations have been ascribed to the malfunction of the peroxisome, a subcellular organelle. The peroxisomal disorders have been divided into three groups: 1) those that result from defective biogenesis of the peroxisome (Zellweger syndrome, neonatal adrenoleukodystrophy, and infantile Refsum's disease); 2) those that result from multiple enzyme deficiencies (rhizomelic chondrodysplasia punctata); and 3) those that result from a single enzyme deficiency (X-linked adrenoleukodystrophy, primary hyperoxaluria type 1). Zellweger syndrome, the most lethal of the three peroxisomal biogenesis disorders, causes infantile hypotonia, seizures, and death within the first year. Ophthalmic manifestations include corneal opacification, cataract, glaucoma, pigmentary retinopathy and optic atrophy. Neonatal adrenoleukodystrophy and infantile Refsum's disease appear to be genetically distinct, but clinically, biochemically, and pathologically similar to Zellweger syndrome, although milder. Rhizomelic chondrodysplasia punctata, a peroxisomal disorder which results from at least two peroxisomal enzyme deficiencies, presents at birth with skeletal abnormalities and patients rarely survive past one year of age. The most prominent ocular manifestation consists of bilateral cataracts. X-linked (childhood) adrenoleukodystrophy, results from a deficiency of a single peroxisomal enzyme, presents in the latter part of the first decade with behavioral, cognitive and visual deterioration. The vision loss results from demyelination of the entire visual pathway, but the outer retina is spared. Primary hyperoxaluria type 1 manifests parafoveal subretinal pigment proliferation. Classical Refsum's disease may also be a peroxisomal disorder, but definitive evidence is lacking. Early identification of these disorders, which may depend on recognizing the ophthalmological findings, is critical for prenatal diagnosis, treatment, and genetic counselling.

Lipoproteins secreted by cultured rat hepatocytes contain the antioxidant 1-alk-1-enyl-2-acylglycerophosphoethanolamine

Monolayer cultures of rat hepatocytes have been examined for their ability to secrete ethanolamine plasmalogen as a component of nascent lipoproteins. In culture medium from these cells, ethanolamine plasmalogen comprises approx. 20-30% of total ethanolamine glycerophospholipids when measured either as phospholipid mass or by the incorporation of [1-3H]ethanolamine. An approximately equal distribution of the plasmalogen was found throughout all lipoprotein density fractions. The content of plasmalogen in whole rat serum, was 36% of total ethanolamine glycerophospholipids. In contrast, in rat liver and cultured hepatocytes the amount of ethanolamine plasmalogen was 5-fold lower than in serum or culture medium (approx. 5% of total ethanolamine phospholipids). Normal human plasma also contains ethanolamine plasmalogen in relatively large amounts (approx. 50% of total ethanolamine phospholipids). Thus, a major function of plasmalogen biosynthetic enzymes in liver may be the provision of ethanolamine plasmalogen for secretion into lipoproteins. Previous studies (e.g., Zoeller, R.A. et al. (1988) J. Biol. Chem. 263, 11590-11596) have suggested that ethanolamine plasmalogen may function as an antioxidant for the protection of lipid and protein membrane components against oxidation. Oxidized, but not native, low-density lipoprotein is rapidly taken up by macrophages with the formation of foam cells characteristic of atherosclerotic lesions (Steinbrecher, U.P. et al. (1984) Proc. Natl. Acad. Sci. USA 81, 3883-3887). Thus, the presence of plasmalogen as part of newly secreted lipoprotein particles may prevent their oxidation and subsequent uptake by macrophages.

Behaviour of plasmalogens during high-performance liquid chromatography on a silica column with a mobile phase containing phosphoric acid

Silica high-performance liquid chromatographic separation of phospho- and sphingolipids of biological origin using a mobile phase containing phosphoric acid leads to gradual hydrolysis of plasmalogens during their passage through the column. The resulting 2-acyl lyso analogues give rise to peaks that tail in the direction of the parent intact plasmalogen. Tailing can be prevented by previous complete acid hydrolysis of plasmalogens. Direct high-performance liquid chromatographic profiling of phospholipids, their plasmalogens (as 2-acyl lyso analogues) and sphingolipids is probably the method of choice for the diagnosis of patients with deficient plasmalogen biosynthesis caused by peroxisomal abnormalities.

Peroxisomal disorders in neurology

Although peroxisomes were initially believed to play only a minor role in mammalian metabolism, it is now clear that they catalyse essential reactions in a number of different metabolic pathways and thus play an indispensable role in intermediary metabolism. The metabolic pathways in which peroxisomes are involved include the biosynthesis of ether phospholipids and bile acids, the oxidation of very long chain fatty acids, prostaglandins and unsaturated long chain fatty acids and the catabolism of phytanate and (in man) pipecolate and glyoxylate. The importance of peroxisomes in cellular metabolism is stressed by the existence of a group of inherited diseases, the peroxisomal disorders, caused by an impairment in one or more peroxisomal functions. In the last decade our knowledge about peroxisomes and peroxisomal disorders has progressed enormously and has been the subject of several reviews. New developments include the identification of several additional peroxisomal disorders, the discovery of the primary defect in several of these peroxisomal disorders, the recognition of novel peroxisomal functions and the application of complementation analysis to obtain information on the genetic relationship between the different peroxisomal disorders. The peroxisomal disorders recognized at present comprise 12 different diseases, with neurological involvement in 10 of them. These diseases include: (1) those in which peroxisomes are virtually absent leading to a generalized impairment of peroxisomal functions (the cerebro-hepato-renal syndrome of Zellweger, neonatal adrenoleukodystrophy, infantile Refsum disease and hyperpipecolic acidaemia); (2) those in which peroxisomes are present and several peroxisomal functions are impaired (the rhizomelic form of chondrodysplasia punctata, combined peroxisomal beta-oxidation enzyme protein deficiency); and (3) those in which peroxisomes are present and only a single peroxisomal function is impaired (X-linked adrenoleukodystrophy, peroxisomal thiolase deficiency (pseudo-Zellweger syndrome), acyl-CoA oxidase deficiency (pseudo-neonatal adrenoleukodystrophy) and probably, the classic form of Refsum disease.

Peroxisomal membrane ghosts in Zellweger syndrome--aberrant organelle assembly

Peroxisomes are apparently missing in Zellweger syndrome; nevertheless, some of the integral membrane proteins of the organelle are present. Their distribution was studied by immunofluorescence microscopy. In control fibroblasts, peroxisomes appeared as small dots. In Zellweger fibroblasts, the peroxisomal membrane proteins were located in unusual empty membrane structures of larger size. These results suggest that the primary defect in this disease may be in the mechanism for import of matrix proteins.

Peroxisomal integral membrane proteins in livers of patients with Zellweger syndrome, infantile Refsum's disease and X-linked adrenoleukodystrophy

Livers from seven patients with peroxisome disorders, three with Zellweger syndrome, one with infantile Refsum's syndrome and three with X-linked adrenoleukodystrophy, were analysed by immunoblotting. The bifunctional protein catalysing two peroxisomal beta-oxidation reactions was deficient in all Zellweger livers and in the infantile Refsum's liver, consistent with the absence of morphologically recognizable peroxisomes. Three peroxisomal integral membrane proteins (IMPs) (69, 53 and 22 kDa) were present in normal amounts in all the Zellweger and adrenoleukodystrophy samples and they sedimented in a membrane fraction. These membrane proteins were also present in the infantile Refsum's liver. We suggest, on the basis of these results, that aberrant peroxisomal membranes may be present in Zellweger syndrome and that the defect is in the transport of matrix proteins into the organelle.

Infantile Refsum disease: an inherited peroxisomal disorder. Comparison with Zellweger syndrome and neonatal adrenoleukodystrophy

Three patients affected by infantile Refsum disease are described with mental retardation, minor facial dysmorphia, chorioretinopathy, sensorineural hearing deficit, hepatomegaly, failure to thrive and hypocholesterolaemia. Initially, only an accumulation of phytanic acid was thought to be present. More recent findings showed a biochemical profile very similar to that found in classical Zellweger syndrome or neonatal adrenoleukodystrophy. Morphologically typical peroxisomes were absent in the liver. All three disorders are associated with multiple peroxisomal dysfunction. Because of these similarities pertinent clinical data of our three patients are compared with those of reported patients diagnosed as having infantile Refsum disease, neonatal adrenoleukodystrophy or Zellweger syndrome who survived for several years. Attention is drawn to the difference in severity of clinical features, ranging from infantile Refsum's disease to neonatal adrenoleukodystrophy and, finally, to Zellweger syndrome.

Cloning and expression of the rat liver cDNA for peroxisomal enoyl-CoA hydratase, 3-hydroxyacyl-CoA dehydrogenase in lambda GT11. Transcriptional regulation of enzyme activity by Wy-14643 in primary cultures of rat hepatocytes

Proliferation of rat liver peroxisomes by the hypolipidemic drug Wy-14643 is associated with a concomitant induction of peroxisomal enzymes involved in the beta-oxidation of fatty acids. In order to explore the molecular mechanism of this induction process we have cloned the cDNA for the peroxisomal bifunctional enzyme enoyl-CoA hydratase, 3-hydroxyacyl-CoA dehydrogenase (ECH) in the lambda gt11 expression vector. The library was screened with the monospecific rabbit antiserum to ECH. Hybrid-selected-mRNA translation established that the immunoreactive clones contain the cDNA sequences of the ECH bifunctional enzyme. The cloned cDNA was used to define the early events associated with enzyme induction in primary cultures of rat hepatocytes. Dot-blot hybridization of the total hepatocyte RNA with the ECH cDNA probe showed that the ECH mRNA begins to rise at about 10-15 h following incubation with Wy-14643. At 24 h and 48 h of incubation the stimulation of the ECH mRNA over the vehicle-treated control reached 26-fold and 47-fold respectively. Run-off experiments in the isolated nuclei of hepatocytes showed no increase in the transcription rate of the ECH gene at 5 h after drug treatment and a 2-fold and 11-fold increase at 10 h and 20 h of drug treatment. From these results we conclude that the increase in ECH activity by Wy-14643 is due to an enhancement of the rate of transcription of the ECH gene. However, the relatively long lag period of about 10-15 h after exposure of hepatocytes to Wy-14643 suggests that the induction of the ECH mRNA may involve an indirect effect of the drug on the transcription of this gene.

Purification of nonspecific lipid transfer protein (sterol carrier protein 2) from human liver and its deficiency in livers from patients with cerebro-hepato-renal (Zellweger) syndrome

The nonspecific lipid transfer protein (i.e., sterol carrier protein 2) from human liver was purified to homogeneity using ammonium sulfate precipitation, CM-cellulose chromatography, molecular sieve chromatography and fast protein liquid chromatography. Its amino acid composition was determined and found to be very similar to that of the nonspecific lipid transfer protein from bovine and rat liver with, as main feature, the absence of arginine, histidine and tyrosine. By way of a specific enzyme immunoassay using affinity-purified antibodies, the levels of nonspecific lipid transfer protein were determined in human livers. Levels varied from approximately 150 ng nonspecific lipid transfer protein per mg 105,000 X g supernatant protein for juvenile and adult humans to 40 ng per mg supernatant protein for a young infant. Levels of nonspecific lipid transfer protein in livers of infants with cerebro-hepato-renal (Zellweger) syndrome were extremely low (i.e., 2 ng per mg supernatant protein). Immunoblotting revealed the presence of crossreactive proteins of molecular masses of 40,000 and 58,000. The 40 kDa and 58 kDa proteins occurred in control livers, whereas only the 40 kDa protein was present in Zellweger livers. As in rat the 58 kDa protein could be demonstrated in a peroxisomal preparation isolated from an adult liver. A possible link between the occurrence of nonspecific lipid transfer protein and the presence of peroxisomes is discussed.

Properties of the enzymes catalyzing the biosynthesis of lysophosphatidate and its ether analog in cultured fibroblasts from Zellweger syndrome patients and normal controls

The activities, properties, and steady-state kinetics of the five enzymes catalyzing the synthesis of 1-acyl- and 1-alkyl-sn-glycerol 3-phosphate in the cultured skin fibroblasts from Zellweger syndrome patients and normal controls were studied in detail. Judging from their Km and Vmax values, glycerol phosphate acyltransferase (EC 2.3.1.15), acyl/alkyl dihydroxyacetone phosphate reductase (EC 1.1.1.101), and acyl coenzyme A reductase (long-chain alcohol forming), appear to be affected only slightly by the absence of peroxisomes characteristic of the Zellweger syndrome. Glycerophosphate acyltransferase also showed no differences in N-ethylmaleimide sensitivity nor in inhibition by dihydroxyacetone phosphate between these cell types. Dihydroxyacetone phosphate acyltransferase (EC 2.3.1.42) and alkyl dihydroxyacetone phosphate synthase (EC 2.5.1.26) have altered activity and kinetic constants in homogenates from Zellweger syndrome fibroblasts. Dihydroxyacetone phosphate acyltransferase has similar Km (DHAP) values in both control and Zellweger syndrome cells; however, the value for the Vmax in Zellweger syndrome cells is only 6% of that found in the controls. This is interpreted as indicating that this enzyme is not defective in this disease but is simply present at a depressed level. Also, this enzyme activity has a maximum rate at pH 7.0-7.5 in the mutant cells as opposed to pH 5.4 in the controls. Acylation of dihydroxyacetone phosphate by control cell homogenate was stimulated by N-ethylmaleimide at both pH 5.7 and 7.5 whereas this activity from Zellweger syndrome cells was slightly inhibited at pH 5.7 and strongly inhibited at pH 7.5. In the absence of detergent, dihydroxyacetone phosphate acyltransferase in the Zellweger syndrome cells was much more labile to trypsin than in the control cells. Alkyl dihydroxyacetone phosphate synthase had a slightly higher Km (33 vs 17 microM) for palmitoyl dihydroxyacetone phosphate and a lower Vmax (0.07 vs 0.24 mU/mg protein) in the Zellweger syndrome cells as compared to controls. Although this is a substantial decrease in activity, it probably contributes little to the decreased rate of ether lipid synthesis in these cells. The major problem in this respect is apparently the loss of dihydroxyacetone phosphate acyltransferase activity. All of these enzymes, in both control and Zellweger syndrome cell homogenates, are sedimentable by centrifugation at 100,000g. Also, with the exception of dihydroxyacetone phosphate acyltransferase they had similar patterns of inactivation by heat in both cell types.

Neonatal adrenoleukodystrophy. Impaired plasmalogen biosynthesis and peroxisomal beta-oxidation due to a deficiency of catalase-containing particles (peroxisomes) in cultured skin fibroblasts

Neonatal adrenoleukodystrophy belongs to the newly recognized group of inherited diseases, the peroxisomal disorders. Based on the reported similarities between neonatal adrenoleukodystrophy and the cerebro-hepato-renal (Zellweger) syndrome, we have studied peroxisomal functions in cultured skin fibroblasts from 5 neonatal adrenoleukodystrophy patients. The results indicate that multiple peroxisomal enzyme activities are deficient in fibroblasts from neonatal adrenoleukodystrophy patients. Digitonin titration experiments revealed that peroxisomes are strongly deficient in these fibroblasts as found earlier in fibroblasts from Zellweger patients. These findings not only explain the generalized loss of peroxisomal functions in neonatal adrenoleukodystrophy, but also provide an explanation for the observed resemblance in clinical and biochemical abnormalities between neonatal adrenoleukodystrophy and Zellweger syndrome. The implications for the pre- and postnatal detection of this disease will be discussed.

Zellweger syndrome: biochemical procedures in diagnosis, prevention and treatment

In patients with cerebro-hepato-renal (Zellweger) syndrome, the absence of peroxisomes results in an impairment of metabolic processes in which peroxisomes are normally involved. These include the catabolism of very long chain (greater than C22) fatty acids, the biosynthesis of ether-phospholipids and of bile acids, the catabolism of phytanic acid and the catabolism of pipecolic acid. Many diagnostic tests for Zellweger syndrome have become available in recent years. In classic Zellweger syndrome abnormal C27-bile acids, very long chain fatty acids, dicarboxylic acids and pipecolic acid accumulate in the plasma of the patients. Moreover, depending upon the diet, plasma phytanic acid concentrations may be elevated. In platelets the activity of acyl-CoA: dihydroxyacetone phosphate acyltransferase is deficient; in erythrocytes from young (less than 4 months) patients the plasmalogen content of the phospholipids is decreased. In cultured fibroblasts from skin and from chorionic villus and cultured amniotic fluid cells from Zellweger patients the plasmalogen level is lowered; there is a decreased activity of acyl-CoA: dihydroxyacetone phosphate acyltransferase, alkyl dihydroxyacetonephosphate synthase and phytanic acid oxidase; the de novo biosynthesis of plasmalogens and the peroxisomal beta-oxidation of fatty acids are impaired and the intracellular localization of catalase is abnormal. Dietary treatment of patients with Zellweger syndrome has not so far resulted in an objective clinical improvement. As Zellweger syndrome is usually fatal in early life, prenatal diagnosis of the disease is important.

Infantile Refsum disease: deficiency of catalase-containing particles (peroxisomes), alkyldihydroxyacetone phosphate synthase and peroxisomal beta-oxidation enzyme proteins

In recent years a number of biochemical abnormalities have been described in patients with the infantile form of Refsum disease, including the accumulation of very long chain fatty acids, trihydroxycoprostanoic acid and pipecolic acid. In this paper we show that catalase-containing particles (peroxisomes), alkyl dihydroxyacetone phosphate synthase and acyl-CoA oxidase protein are deficient in patients with infantile Refsum disease. These findings suggest that in the infantile form of Refsum disease, as in the cerebro-hepato-renal (Zellweger) syndrome the multiplicity of biochemical abnormalities is due to a deficiency of peroxisomes and hence to a generalized loss of peroxisomal functions. As a consequence the infantile form of Refsum disease can be diagnosed biochemically by methods already available for the prenatal and postnatal diagnosis of the cerebro-hepato-renal (Zellweger) syndrome.

Arthrogryposis multiplex congenita: spectrum of pathologic changes

The pathologic features of muscle and/or spinal cord were studied in 96 infants and children with contractures of multiple joints (arthrogryposis multiplex congenita), usually in association with other congenital abnormalities. Ninety of these infants had a neurogenic form of arthrogryposis, and six had primary muscle disease. The neurogenic form, unlike the myopathic form, was usually associated with other congenital abnormalities. The most frequently associated congenital changes were low-set ears, micrognathia, wide flat nose, short neck, congenital heart disease, high-arched palate, hypoplastic lungs, and cryptorchidism. Some of the associated abnormalities could be attributed to muscle weakness, occurring during intrauterine development. A variety of skeletal muscle changes were observed, including primary myopathic alterations, fiber type predominance and disproportion, hypoplasia, aplasia, and denervation atrophy. When the primary alterations were in the spinal cord, abnormalities of anterior horn cells of several distinct types were recognized--absence of cells, diminution, dysgenesis, degeneration, and axonal reaction. The changes in anterior roots corresponded to those of the anterior horn cells.

How proteins get into microbodies (peroxisomes, glyoxysomes, glycosomes)

All microbody proteins studies, including one microbody membrane protein, are made on free polysomes and imported post-translationally. This holds for animal tissues, plants, and fungi. The majority of microbody protein sub-units are synthesized in a form not detectably different from mature sub-units. In five cases a larger precursor protein has been found. The position of the extra piece in this precursor is not known. In two of the five cases, processing of the precursor is not coupled to import; in the other three this remains to be determined. It is not even known whether information in the prepiece contributes to topogenesis, or serves other purposes. Microbody preparations from Neurospora, plant tissue and rat liver can take up some newly synthesized microbody proteins in vitro. In most cases uptake is inefficient. No special requirements for uptake have been established and whether a receptor is involved is not yet known. Several examples have been reported of peroxisomal enzymes with a counterpart in another cell compartment. With the exception of catalase, no direct evidence is available in any of these cases for two isoenzymes specified by the same gene. In the Zellweger syndrome, a lethal hereditary disease of man, characterized by a lack of peroxisomes, the levels of several enzymes of lipid metabolism are strongly decreased. In contrast, D-amino-acid oxidase, L-alpha-hydroxyacid oxidase and catalase levels are normal. The catalase resides in the cytosol. Since there is no separate gene for cytosolic catalase, the normal catalase levels in Zellweger cells show that some peroxisomal enzymes can mature and survive stably in the cytosol. It is possible that maturation of the peroxisomal enzyme in the cytoplasm can account for the finding of cytosolic catalase in some normal mammalian cells. The glycosomes of trypanosomes are microbodies that contain a glycolytic system. Comparison of the glycosomal phosphoglycerate kinase with its cytosolic counterpart has shown that these isoenzymes are 93% homologous in amino-acid sequence, but less than 50% homologous to the corresponding enzymes of yeast and mammals. This implies that few alterations are required to direct a protein into microbodies. This interpretation is supported by the evidence for homology between some microbody and mitochondrial isoenzymes in other organisms mentioned under point 4. The major changes of the glycosomal phosphoglycerate kinase relative to the cytosolic enzyme are a large increase in positive charge and a C-terminal extension of 20 amino acids.(ABSTRACT TRUNCATED AT 400 WORDS)

Neonatal adrenoleukodystrophy: new cases, biochemical studies, and differentiation from Zellweger and related peroxisomal polydystrophy syndromes

Eight new cases of autopsy-confirmed or suspected neonatal adrenoleukodystrophy (NALD) are presented together with new biochemical data on very-long-chain fatty acids (VLCFA) and plasmalogens and a review of all previously published cases. The clinical, biochemical, and histopathologic abnormalities characteristic of this newly recognized form of adrenoleukodystrophy are analyzed in detail and compared to the principal characteristics of the similar disorder, the cerebrohepatorenal syndrome of Zellweger (ZS). Using strict pathologic criteria for the diagnosis of NALD, we find that, despite many clinical resemblances, NALD and the ZS are distinguishable on the basis of histology and peroxisomal biochemistry. Patients with NALD demonstrate adrenal atrophy, systemic infiltration by abnormal lipid-laden macrophages, and elevations of saturated VLCFA. In contrast, patients with ZS have chondrodysplasia, glomerulocystic disease of the kidney, central nervous system dysmyelination, and elevations of unsaturated as well as saturated VLCFA, but they lack adrenal atrophy. We conclude that NALD and the ZS probably represent at least two different genetic defects.

Age-related differences in plasmalogen content of erythrocytes from patients with the cerebro-hepato-renal (Zellweger) syndrome: implications for postnatal detection of the disease

Phosphatidylethanolamine plasmalogen levels were determined in erythrocytes from controls and 13 patients with the cerebro-hepato-renal (Zellweger) syndrome. It was found that in Zellweger patients 20 weeks of age or younger, erythrocyte phosphatidylethanolamine plasmalogen levels were lowered whereas in older patients (except in one) normal levels were found. The results obtained suggest a close relationship between the age of the patients at sampling and the phosphatidylethanolamine plasmalogen levels in their erythrocytes. A possible explanation for these findings and the implications for the postnatal detection of Zellweger syndrome are discussed.

Characterization of peroxisomes in Chinese hamster ovary cells in culture

In order to explore the potential value of Chinese hamster ovary (CHO) cells for the isolation of peroxisomal mutants defective in the peroxisomal fatty acid oxidation system, some characteristics of their peroxisomes were studied. Catalase was detected biochemically and histochemically in peroxisome-like particles in cells or in subcellular fractions prepared by differential centrifugation or isopyknic equilibrium in Percoll or Metrizamide with catalase in the high density fractions of the isopyknic equilibrium gradients. By oxidation system, exhibited an unusually high specific activity, 2.46 +/- 1.09 mU/mg protein, in CHO cell homogenates, a value comparable to that of rat liver. This enzyme copurifies with catalase in the high density fractions of the isopycnic equilibrium gradients. By analogy with other cell types and from the ultrastructural analysis, it is concluded that these enzymes are contained in peroxisomes. These findings support the value of CHO cells for studies of peroxisomal function and organization.

The effect of temperature- and oxygen-acclimation on phospholipids of goldfish (Carassius auratus L.) brain mitochondria

Goldfish (Carassius auratus L.) were temperature- and oxygen-acclimated and the composition of the phospholipids and their acyl groups in brain mitochondria was determined. The proportion of ethanolamine to choline phospholipid was greater while the plasmenyl ethanolamine value (P-GPE/D- + P-GPE) was lower at the low acclimation temperature. For the ethanolamine glycerophospholipids, a rise in the ratio n-6/n-3 fatty acyl groups occurred with cold acclimation. No significant change in the ratio was exhibited by phosphatidyl choline. When the oxygen level was increased, at either acclimation temperature, a rise in the GPE/GPC ratio and the plasmenyl ethanolamine value resulted. The n-6/n-3 ratio was generally increased for the ethanolamine classes when the oxygen concentration was raised. The possible significance of these changes is discussed.

The correlation between biochemical and histopathological findings in adrenoleukodystrophy

Nine areas of the brain from a case of adrenoleukodystrophy were examined histopathologically and by gas chromatography for fatty acid content. The main findings were: (1) the degree of demyelination was related to the pentacosanoic and hexacosanoic to docosanoic acid ratios (C25:0/C22:0 and C26:0/C22:0); gliosis was related to the ratios of several fatty acids to docosanoic acid; (2) there was a shift towards smaller components (C22:0, C23:0, C24:0) of the saturated fatty acid series in the less affected areas, to larger components and various minor components in regions of active demyelination; (3) mainly saturated fatty acids of the middle class components (C24:0, C25:0 and C26:0) were found in severely affected areas where the active process is complete. Because a region of high long chain fatty acid content, lacking histopathological change, was detected, the hypothesis is presented that the primary event in childhood ALD is related to defective lipid metabolism and that this preceeds demyelination.

Purification of peroxisomes from livers of normal and clofibrate-treated mice

A method for the isolation of peroxisomes from livers of normal and clofibrate-treated mice is described. The method utilizes glutaraldehyde to stabilize peroxisomal membranes, and isopycnic centrifugation of a light mitochondrial fraction through a linear metrizamide gradient to achieve optimal resolution from other organelles. On the basis of the biochemical and morphological data, the peroxisomal preparations are indicated as of high purity: contamination by mitochondria, lysosomes, and plasma membranes is negligible, and the level of contaminating microsomes is around 5% for normal peroxisomes and 8% for peroxisomes from clofibrate-treated mice. Peroxisomal membranes prepared by carbonate extraction contain two major polypeptides of approximately 70,000 Da, and show 2 and 8% contamination by microsomal membrane protein for the preparations from normal and clofibrate-treated mice, respectively.

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

Cerebro-hepato-renal (Zellweger) syndrome, adrenoleukodystrophy, and Refsum's 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 Refsum's disease, to an increase in a number of structurally distinct metabolites, as in neonatal ALD/Zellweger syndrome, and infantile Refsum's 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 Refsum's disease suggests that the basic biochemical lesion in each may be similar or at least closely related.

Peroxisomal beta-oxidation enzyme proteins in the Zellweger syndrome

The absence of peroxisomes in patients with the cerebro-hepato-renal (Zellweger) syndrome is accompanied by a number of biochemical abnormalities, including an accumulation of very long-chain fatty acids. We show by immunoblotting that there is a marked deficiency in livers from patients with the Zellweger syndrome of the peroxisomal beta-oxidation enzyme proteins acyl-CoA oxidase, the bifunctional protein with enoyl-CoA hydratase and 3-hydroxyacyl-CoA dehydrogenase activities and 3-oxoacyl-CoA thiolase. Using anti-(acyl-CoA oxidase), increased amounts of cross-reactive material of low Mr were seen in the patients. With anti-(oxoacyl-CoA thiolase), high Mr cross-reactive material, presumably representing precursor forms of 3-oxoacyl-CoA thiolase, was detected in the patients. Catalase protein was not deficient, in accordance with the finding that catalase activity is not diminished in the patients. Thus in contrast to the situation with catalase functional peroxisomes are required for the stability and normal activity of peroxisomal beta-oxidation enzymes.

Identification of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestan-26-oic acid, an intermediate in cholic acid synthesis, in the plasma of patients with infantile Refsum's disease

The plasma bile acid profiles of three children with the inherited metabolic disorder, infantile Refsum's disease, were found to contain 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestan-26-oic acid. This intermediate in the synthesis of cholic acid was identified by combined gas-liquid chromatography-mass spectrometry and accounted for approximately 25% of the total bile acids which were present at elevated concentrations in plasma. Infantile Refsum's disease appears to share several biochemical features with the cerebro-hepato-renal syndrome (Zellweger's disease), including abnormal bile acid metabolism.

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 Refsum's disease, and in the cerebro-hepato-renal (Zellweger's) syndrome. The plasma of patients with the infantile but not the adult form of Refsum's disease contains increased amounts of pipecolic acid and of at least two abnormal bile acids, one of which has been identified as 3 alpha, 7 alpha, 12 alpha trihydroxy-5 beta-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 Zellweger's syndrome and the infantile form of Refsum's disease.

Deficiency of enzymes catalyzing the biosynthesis of glycerol-ether lipids in Zellweger syndrome. A new category of metabolic disease involving the absence of peroxisomes

The Zellweger cerebro-hepato-renal syndrome is a genetic disease characterized by the absence of peroxisomes and deficiency of glycerol-ether lipids in several tissues. We measured the activity of dihydroxyacetone phosphate (DHAP) acyltransferase, a peroxisomal enzyme with a major role in ether lipid synthesis, in fibroblasts and leukocytes from patients with Zellweger syndrome. Control skin and amniotic-fluid fibroblasts had normal activity of DHAP acyltransferase (0.28 to 0.3 nmol per minute per milligram of protein), whereas fibroblasts from three patients with Zellweger syndrome had deficient activity (0.013 +/- 0.006 nmol per minute per milligram of protein). The activity of the enzyme in leukocytes and levels of plasmalogens (the major class of cellular glycerol-ether lipids) in erythrocytes were also deficient in a patient, but normal levels of leukocyte enzyme and erythrocyte plasmalogens were found in her parents. Other enzymes of the acyl DHAP pathway exhibited alterations in fibroblasts from patients with Zellweger syndrome, and the activity of the glycerophosphate acyltransferase was also reduced. These results support prior studies emphasizing the role of peroxisomes and the acyl DHAP pathway in cellular ether lipid synthesis, establish Zellweger syndrome cells as valuable for elucidating peroxisomal functions, and provide prenatal and postnatal diagnostic assays as well as potential therapeutic strategies for Zellweger syndrome.

Deficiency of plasmalogens in the cerebro-hepato-renal (Zellweger) syndrome

We have analyzed the phospholipid composition of various organs of patients with the cerebro-hepato-renal (Zellweger) syndrome. The phospholipid composition of tissues from controls and patients was very similar except for their plasmalogen contents. In controls about 50% of the phosphatidylethanolamine fraction of brain, heart, kidney and skeletal muscle and about 10% of that fraction in control liver tissue was found to consist of plasmalogen. In control heart muscle, but not in other control tissues about 25% of the phosphatidylcholine fraction consist of plasmalogens. In contrast, plasmalogens were nearly absent in the corresponding tissues of Zellweger patients. The amount of phosphatidylethanolamine plasmalogens in both erythrocytes and fibroblasts of Zellweger patients is lowered significantly compared to control erythrocytes and control fibroblasts respectively, although this reduction is not as dramatic as in brain, heart, kidney, skeletal muscle and liver of patients. Phosphatidylcholine-plasmalogens are only present in low amounts in both controls, heterozygotes and patients. In recent years considerable evidence has accumulated to show that peroxisomes are involved in cellular lipid metabolism. Notably, the key enzymes of ether lipid (plasmalogen) biosynthesis in rodents were recently found to be located in peroxisomes. Since electronmicroscopic studies have shown that peroxisomes are absent in liver and kidney of patients with the cerebro-hepato-renal syndrome, our results suggest that an inability to integrate these key enzymes in a functional peroxisome leads to a severe disturbance in plasmalogen biosynthesis. We propose that the multiple clinical and biochemical defects in Zellweger patients are secondary to a deficiency in peroxisomal function.

Severe plasmalogen deficiency in tissues of infants without peroxisomes (Zellweger syndrome)

The Zellweger syndrome is a lethal hereditary disease characterized by the absence of peroxisomes (microbodies) in liver and kidney, and variable abnormalities in mitochondria. We show here that tissues from five infants that had died of this syndrome contain less than 10% of the normal levels of phosphatidylethanolamine plasmalogen (pPE), a major phospholipid component of cellular membranes. Heart and muscle, but not other tissues, also contain a substantial fraction of phosphatidylcholine plasmalogen (pPC), and this fraction is also strongly reduced in the Zellweger patients. No other abnormalities in cellular phospholipids were detected. Key enzymes of the biosynthesis of plasmalogens have previously been shown to be exclusively located in the peroxisomes of rodent liver and the microperoxisomes of rodent brain. We infer that the corresponding enzymes are also located in peroxisomes in man and that the absence of peroxisomes in Zellweger patients leads to their inability to synthesize plasmalogens. Our results support the notion that the biosynthetic role of peroxisomes in mammals has thus far been underestimated. We suggest that the defect in plasmalogen synthesis and possibly as yet unknown peroxisomal reactions are responsible for the diverse abnormalities observed in Zellweger patients.