Joseph Vamecq

Pseudo-Zellweger syndrome: Deficiencies in several peroxisomal oxidative activities

We describe an infant girl with a clinical, chemical, and pathologic syndrome remarkably similar to Zellweger cerebrohepatorenal syndrome but whose liver parenchymal cells contained abundant peroxisomes. Peroxisomal L-alpha hydroxy acid oxidase, catalase, and the plasmalogen synthesizing enzyme dihydroxy acetone phosphate-acyl transferase activities were normal; other peroxisomal enzymatic activities, including fatty acyl-CoA oxidase and D-amino acid oxidase, were reduced by 80% to 85%. Oxidation of bile acids and pipecolic acid was also deficient. Autopsy revealed the presence of neuronal heterotopia, renal cortical cysts, adrenal atrophy, and accumulation of very long chain fatty acids. The clinical and pathologic features of this case of pseudo-Zellweger syndrome reflect a deficiency in multiple peroxisomal activities rather than a defect in peroxisomal biogenesis. The deficient enzymatic activities require flavin adenine dinucleotide, and the underlying defect may be in the utilization of this cofactor.

Effect of various n − 3/n − 6 fatty acid ratio contents of high fat diets on rat liver and heart peroxisomal and mitochondrial β-oxidation

The present work extends tissue investigations previously performed in rat gastric mucosa on lipid metabolism alterations caused by n-3 and n-6 fatty acid-enriched diets. Liver and heart tissues are here studied and demonstrated to undergo, upon exposure to high fat diets with various n-3/n-6 fatty acid ratio contents, biochemical and morphological changes which may be enumerated as follows: (1) Rat liver peroxisomal prostaglandin E2, fatty acid but not bile acid beta-oxidation rates are enhanced, especially upon the diet with the higher n-3/n-6 fatty acid ratio. Mitochondrial beta-oxidation rates are little or not affected by the high fat diets. (2) Rat liver carnitine acyltransferases are stimulated by the high fat diets, the more rich the n-3 fatty acid content, the more pronounced the stimulatory effect. (3) Rat heart peroxisomal and mitochondrial beta-oxidation rates were increased in animals receiving the n-3 fatty acid-enriched diet. At a low n-3/n-6 fatty acid ratio content of the diet, these oxidizing rate values were in control range. The carnitine acyltransferase activities were increased in rat heart to different extents, depending on the n-3/n-6 fatty acid ratio content of the diet. (4) Ultrastructural examination and morphometric determinations on hepatocytes from rats receiving the diets with the lowest and the highest n-3/n-6 fatty acid ratio contents disclose that in the latter case the numbers and fractional volumes of peroxisomes and mitochondria are significantly higher than in the former case.

Atypical Riboflavin-responsive Glutaric Aciduria, and Deficient Peroxisomal Glutaryl-coa Oxidase Activity - a New Peroxisomal Disorder

SummaryInvestigation of cultured skin fibroblasts in a patient with atypical riboflavin-responsive glutaric acidura revealed a marked deficiency of peroxisomal glutaryl-CoA oxidase. This is the first patient to be reported with glutaric aciduria caused by a peroxisomal rather than a mitochondrial dysfunction. This enzyme appears to be specific for glutaryl-CoA, as lauryl-CoA and dodecanedioyl-CoA oxidase activities in the fibroblasts were both normal. The urinary excretion of glutaric acid (0.5 mmol mmol creatinine−1) suggests that the flux through this pathway is considerably less than the mitochondrial flux through glutaryl-CoA dehydrogenase. The elevated glutaric acid excretion (to 0.8 mmol mmol creatinine−1) in response to lysine loading suggests that lysine is a precursor.

Fluorometric assay of peroxisomal oxidases.

The present paper deals with the adaptation of the fluorometric measurement of H2O2 originally described by Guilbault et al. (1967, Anal. Chem. 39, 271) for the assay of the peroxisomal oxidation of D-amino acids, L-alpha-hydroxyacids, uric acid, and acyl-CoA esters. The present work essentially covers three facets: (i) the general kinetics of the assay of peroxisomal oxidases and the influence of each component of the assay medium on these kinetics; (ii) the measurement of peroxisomal oxidase activities in subcellular fractions and tissues from human and untreated and clofibrate-treated rodents; and (iii) the comparison between the oxidase activities measured by the fluorometric and spectrophotometric methods.

Comparative Anticonvulsant Activity and Neurotoxicity of 4–Amino-N-(2,6-Dimethylphenyl)Phthalimide and Prototype Antiepileptic Drugs in Mice and Rats

Summary: We compared the anticonvulsant activity and neurotoxicity of 4‐amino‐N‐(2,6–dimethyl‐phenyl)phthalimide (ADD213063)with those of phenytoin (PHT), carbamazepine (CBZ), phenobarbital (PB), ethosuximide (ESM), valproate (VPA), and felbamate (FBM). Evaluation of anticonvulsant properties performed according to well‐established procedures in rats and mice showed that ADD 213063 is most effective in protecting animals against maximal electroshock seizures (MES). This anti‐MES activity is achieved with nontoxic doses, with the optimal effect recorded in rats dosed orally with anti‐MES ED, and protective index (PI) values of 25.2 FmoYkg and >75, respectively. ADD 213063 protects to a lesser extent against seizures induced by subcutaneous (s.c.) picrotoxin and subcutaneous pentylenetetrazol(FTZ) in mice dosed intraperitoneally and orally, respectively. The profile of anticonvulsant action of ADD 213063 closely parallels that of CBZ.

Altered acyl-CoA metabolism in riboflavin deficiency.

We have recently described the effects of riboflavin deficiency on the metabolism of dicarboxylic acids (Draye et al. (1988) Eur. J. Biochem. 178, 183-189). As both mitochondria and peroxisomes are thought to be involved, we have examined the activities of various enzymes in these organelles in the livers of riboflavin-deficient rats. Mitochondrial beta-oxidation of fatty acids was severely depressed due to loss of activity of the three fatty acyl-CoA dehydrogenases, whereas there was an enhancement of peroxisomal beta-oxidation due to an increased activity of the FAD-dependent fatty acyl-CoA oxidase, although the activities of other peroxisomal flavoproteins, D-amino acid oxidase and glycolate oxidase, were lowered. Hepatocyte morphometry revealed an increase in the numbers of peroxisomes, indicating a proliferation induced by the deficiency. The mitochondrial acyl-CoA dehydrogenases involved in branched-chain amino acid metabolism were also severely decreased leading to characteristic organic acidurias. There was some loss of activity of the flavin-dependent sections of the electron transport chain (complexes I and II), but these were probably not sufficient to affect normal function in vivo. The specificity of these effects allows the use of the riboflavin-deficient rat as a model for the study of dicarboxylate metabolism.

Bile acids in peroxisomal disorders

Abstract. We examined serum bile acids in patients with different peroxisomal disorders. Patients with Zellweger syndrome (n= 23), infantile form of Refsum disease (n= 6) and neonatal adrenoleukodystrophy (n= 4) consistently had increased levels of bile acid precursors. Patients with X‐linked adrenoleukodystrophy, (n= 5) classical Refsum disease (n= 3), hyperpipecolic acidaemia (n= 4) and rhizomelic chondrodysplasia punctata (n= 9) did not have increased bile acid precursor levels. Total serum bile acids (41 μg ml‐1) and the percentage of bile acid precursors (80%) were highest in typical Zellweger patients who died young. Long‐living Zellweger patients, neonatal adrenoleukodystrophy patients and infantile Refsum disease patients had, on average, less cholestasis and a lower percentage of bile acid precursors. We also observed that total serum bile acids and the percentage of bile acid precursors decreased with age in longliving Zellweger patients. Screening for bile acid precursors, combined with very long chain fatty acids analysis is, in our experience, an easy and reliable firstline approach to the detection of peroxisomal disorders.

Screening for primary creatine deficiencies in French patients with unexplained neurological symptoms.

A population of patients with unexplained neurological symptoms from six major French university hospitals was screened over a 28-month period for primary creatine disorder (PCD). Urine guanidinoacetate (GAA) and creatine:creatinine ratios were measured in a cohort of 6,353 subjects to identify PCD patients and compile their clinical, 1H-MRS, biochemical and molecular data. Six GAMT [N-guanidinoacetatemethyltransferase (EC 2.1.1.2)] and 10 X-linked creatine transporter (SLC6A8) but no AGAT (GATM) [L-arginine/glycine amidinotransferase (EC 2.1.4.1)] deficient patients were identified in this manner. Three additional affected sibs were further identified after familial inquiry (1 brother with GAMT deficiency and 2 brothers with SLC6A8 deficiency in two different families). The prevalence of PCD in this population was 0.25% (0.09% and 0.16% for GAMT and SLC6A8 deficiencies, respectively). Seven new PCD-causing mutations were discovered (2 nonsense [c.577Cu2009>u2009T and c.289Cu2009>u2009T] and 1 splicing [c.391u2009+u200915Gu2009>u2009T] mutations for the GAMT gene and, 2 missense [c.1208Cu2009>u2009A and c.926Cu2009>u2009A], 1 frameshift [c.930delG] and 1 splicing [c.1393-1Gu2009>u2009A] mutations for the SLC6A8 gene). No hot spot mutations were observed in these genes, as all the mutations were distributed throughout the entire gene sequences and were essentially patient/family specific. Approximately one fifth of the mutations of SLC6A8, but not GAMT, were attributed to neo-mutation, germinal or somatic mosaicism events. The only SLC6A8-deficient female patient in our series presented with the severe phenotype usually characterizing affected male patients, an observation in agreement with recent evidence that is in support of the fact that this X-linked disorder might be more frequent than expected in the female population with intellectual disability.

Stroke, hemiparesis and deficient mitochondrial β-oxidation

We describe on a 3-year-old child referred for evaluation and therapy of a cerebral vascular accident with residual hemiplegia and partial epilepsy. Metabolic investigations initially showed normal urinary organic acids as well as normal blood and urinary amino acids. Blood carnitine fractions had been pathological and a secondary carnitine deficiency was diagnosed and treated by oral L-carnitine supplementation. During carnitine treatment, abnormal urinary acylcarnitine profiles were noticed with excessive amounts of several carnitine esters including propionylcarnitine, butyryl-and/or isobutyryl-carnitine, isovaleryl- and/or 2-methylbutyryl-carnitine, hexanoylcarnitine and octanoyl-carnitine. Subsequently, an urinary organic acid profile suggestive of glutaric aciduria type 11 was recorded during a clinical decompensation crisis. Morphological and biochemical studies on skeletal muscle and skin fibroblasts were performed and confirmed the existence of a defect of the mitochondrial β-oxidadation pathways with lipidic myopathy, reduced palmitate and octanoate oxidation rates in cultured fibroblasts. Glutaric aciduria type 11 increases the list of metabolic disorders characterized by hemiplegia and other sequelae of brain ischaemia such as stroke-like episode, seizures, aphasia, ataxia and myoclonia, similar to those seen in MELAS.

Mitochondrial dysfunction and lipid homeostasis.

This review is aimed at illustrating that mitochondrial dysfunction and altered lipid homeostasis may concur in a variety of pathogenesis states, being either contributive or consecutive to primary disease events. Underlying mechanisms for this concurrence are far from being the exhaustive elements taking place in disease development. They may however complicate, contribute or cause the disease. In the first part of the review, physiological roles of mitochondria in coordinating lipid metabolism and in controlling reactive oxygen species (ROS), ATP and calcium levels are briefly presented. In a second part, clues for how mitochondria-driven alterations in lipid metabolism may induce toxicity are discussed. In the third part, it is illustrated how mitochondrial dysfunction and lipid homeostasis disruption may be associated (i) to complicate type 1 diabetes (pancreatic β-cell mitochondrial dysfunction in ATP yield induces reduced insulin secretion and hence disruption of glucose and lipid metabolism), (ii) to contribute to type 2 diabetes and other insulin resistant states (mitochondrial impairment may induce adipocyte dysfunction with subsequent increase in circulating free fatty acids and their abnormal deposit in non adipose tissues (pancreatic β-cells, skeletal muscle and liver) which results in lipotoxicity and mitochondrial dysfunction), (iii) to offer new clues in our understanding of how the brain controls feeding supply and energy expenditure, (iv) to promote cancer development notably via fatty acid oxidation/synthesis imbalance (in favor of synthesis) further strengthened in some cancers by a lipogenetic benefit induced by a HER2/fatty acid synthase cross-talk, and (v) to favor cardiovascular disorders by impacting heart function and arterial wall integrity.