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J Vamecq

Publications and source records attributed to J Vamecq.

At least 55 records · Page 3Linked to original sources
PubMed1990

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.

Animals↗
PubMed1990

Peroxisome proliferation and modulation of rat liver carcinogenesis by 2,4-dichlorophenoxyacetic acid, 2,4,5-trichlorophenoxyacetic acid, perfluorooctanoic acid and nafenopin.

Using an initiation--selection--promotion protocol for induction of liver tumors in Wistar rats, the modulating action of various peroxisome proliferators on neoplasia as well as on selected biochemical parameters was studied. After treatment with diethylnitrosamine (DEN), the animals were subsequently subjected to a selection procedure involving feeding of 2-acetylaminofluorene (2-AAF), and in the middle of the 2-AAF treatment, a single necrogenic dose of carbon tetrachloride. Following a recovery period, the rats were fed a diet containing 0.1% nafenopin (NAF), 0.015% perfluorooctanoic acid (PFOA), 0.05% 2,4-dichlorophenoxyacetic acid (2,4-D), 0.05% 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) or 0.05% phenobarbital (PB) as a positive control. When the animals were killed, 7 months after initiation, the incidence of hepatocellular carcinoma was 83, 33 and 16% in the animals treated with NAF, PFOA or 2,4,5-T respectively. No cancers were observed in controls, or in the 2,4,-D groups. In comparison with controls, NAF and PFOA caused a 60-and 24-fold increase inthe peroxisomal beta-oxidation of fatty acids respectively, but only about a 2-fold increase in the catalase activity, 2,4-D and/or 2,4,5-T were much less active in this respect, giving approximately a doubling in the rate of fatty acid oxidation. The specific activity of D-amino acid and glycolate oxidases were significantly depressed, whereas the urate oxidase levels were apparently unaffected by the NAF and PFOA treatment. The results suggest that the selective induction of peroxisomal fatty acid oxidation is consistent with the hypothesis that imbalance between H2O2 overproduction and its destruction could play a role in the modulation of hepatocarcinogenesis by peroxisome proliferators.

2,4,5-Trichlorophenoxyacetic Acid↗
PubMed1990

Studies on the metabolism of glycolyl-CoA.

Glycolyl-CoA can be formed during the course of the beta-oxidation by rat liver mitochondria of 4-hydroxybutyrate. The existence of this beta-oxidation has been previously supported by the occurrence of 4-hydroxybutyrate and its beta-oxidation catabolites in urine from patients with 4-hydroxybutyric aciduria, an inborn error of gamma-aminobutyric acid metabolism due to the deficiency of succinic semialdehyde dehydrogenase. The characteristics of the mitochondrial beta-oxidation of 4-hydroxybutyrate were, in rat liver, compared with those of the mitochondrial beta-oxidation of butyrate. The inhibition by malonate of the oxidation of 4-hydroxybutyrate was about twofold weaker than that of oxidation of butyrate, whereas both oxidations were abolished by preincubating the mitochondria with 1 mM valproic acid, a known inhibitor of mitochondrial beta-oxidation. Mitochondria from rat kidney cortex were demonstrated to catalyse, as previously shown for hepatic mitochondria, the carnitine-dependent oxidation of 12-hydroxylauroyl-CoA-omega-Hydroxymonocarboxylyl-CoAs are thus concluded to be precursors of glycolyl-CoA also in rat kidney cortex. In addition, 3-hydroxypyruvate was found to be a precursor of glycolyl-CoA, since it was oxidized by bovine heart pyruvate dehydrogenase with a cofactor requirement similar to that of pyruvate oxidation. Glycolyl-CoA was a substrate of carnitine acetyltransferase (pigeon breast muscle). Pig heart citrate synthase was capable of catalyzing the condensation of glycolyl-CoA with oxaloacetate. The product of this reaction induced low NADH production rates dependent on the addition of porcine heart aconitase and isocitrate dehydrogenase.

Acetate-CoA Ligase↗
PubMed1989

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.

Acyl Coenzyme A↗
PubMed1989

Comparison between the formation and the oxidation of dicarboxylylcarnitine esters in rat liver and skeletal muscle: possible implications for human inborn disorders of mitochondrial beta-oxidation.

The activity of dicarboxylyl-CoA synthetase previously reported in rat liver was detected, in the presence of added detergents, in rat skeletal muscle. In both tissues, carnitine dicarboxylyltransferase activities were recorded but their substrate chain length specificity was, however, different. In rat skeletal muscle, but not liver, a carnitine-dependent oxidation by intact mitochondria of dodecanedioyl-CoA was easily detected by the spectrophotometric measurement of the substrate-dependent ferricyanide reduction. The implications of the present data for the pathogenesis of disorders with excess urine dicarboxylylcarnitine esters are discussed.

Animals↗
PubMed1989

Effects of dietary corn oil and salmon oil on the oxidation of fatty acids and prostaglandin E2 in rat gastric mucosa.

The investigations previously carried out by Grataroli and colleagues (1) to elucidate the relationships between dietary fatty acids, lipid composition, prostaglandin E2 production and phospholipase A2 activity in the rat gastric mucosa are, here, extended. In the present investigations, fatty acid and prostaglandin E2 catabolizing enzymes were assayed in gastric mucosa from rats fed either a low fat diet (corn oil: 4.4% w/w) (referred as control group), a corn oil-enriched diet (17%) or a salmon oil-enriched diet (12.5%) supplemented with corn oil (4.5%) (referred as groups of treated animals) for eight weeks. Peroxisomal fatty acyl-CoA beta-oxidation was induced in the treated animals whereas the activities of catalase and mitochondrial tyramine oxidase were increased and normal, respectively. Mitochondrial acyl-CoA dehydrogenations occurred at higher rates and carnitine acyltransferase activities were enhanced. In addition, the induction of peroxisomal but not mitochondrial prostaglandoyl-E2-CoA beta-oxidation could be demonstrated. Induction of peroxisomal oxidation of fatty acids and prostaglandins is suggested to contribute to the decrease of prostaglandin E2 production in the treated animals, especially those receiving the salmon oil diet, that the above mentioned authors originally reported.

Animals↗
PubMed1989

Developmental patterns of peroxisomal enzymes in amphibian liver during spontaneous and triiodothyronine-induced metamorphosis.

1. Liver catalase, D-amino acid oxidase, urate oxidase of Alytes obstetricans and Xenopus laevis (anuran amphibians) and fatty acyl-CoA oxidase of Alytes were present at all post-embryonic stages. 2. Catalase and D-amino acid oxidase activities increased during spontaneous metamorphosis of the two species. 3. During triiodothyronine-induced metamorphosis of Alytes larvae, catalase and D-amino acid oxidase activities increased after a latent period. 4. Our results suggest that expression of some hepatic peroxisomal enzymes is modulated by thyroid hormones.

Animals↗
PubMed1989

The gluconeogenicity of fatty acids in mammals.

Although excess glucose can be readily converted to fatty acids in mammals, most textbooks state that glucose cannot be formed from fatty acids. Whilst this remains largely true, several pathways have now been discovered in mammals in which fatty acids are potentially gluconeogenic.

Animals↗
PubMed1989

Peroxisomal and mitochondrial beta-oxidation of monocarboxylyl-CoA, omega-hydroxymonocarboxylyl-CoA and dicarboxylyl-CoA esters in tissues from untreated and clofibrate-treated rats.

In control rats, long-chain monocarboxylyl-CoA, omega-hydroxymonocarboxylyl-CoA, and dicarboxylyl-CoA esters were substrates for hepatic, renal, and myocardial peroxisomal beta-oxidation. The latter enzyme system could not be detected in skeletal muscle. Clofibrate treatment resulted in an enhancement of peroxisomal beta-oxidizing capacity in various tissues. Intact mitochondria from control rat liver and kidney cortex incubated in the presence of L-carnitine were capable of oxidizing long-chain monocarboxylyl-CoAs and omega-hydroxymonocarboxylyl-CoAs but not dicarboxylyl-CoAs. However, control rat liver mitochondria permeabilized by digitonin oxidized dodecanedioyl-CoA indicating that the liver mitochondrial beta-oxidation system can act on dicarboxylyl-CoA esters even if the overall intact mitochondrial system is inactive on these substrates. Intact liver mitochondria from clofibrate-treated animals rapidly oxidized lauroyl-CoA and 12-hydroxylauroyl-CoA but not dodecanedioyl-CoA. These mitochondria were active on hexadecanedioyl-CoA and this activity amounted to 20-25% of that measured with palmitoyl-CoA and 16-hydroxypalmitoyl-CoA as substrates. No mitochondrial dicarboxylyl-CoA oxidation could be detected in kidney cortex from animals receiving clofibrate in their diet. Heart and skeletal muscle intact mitochondria from untreated and clofibrate-treated rats were capable of oxidizing each type of acyl-CoA as a substrate. Dicarboxylyl-CoA synthetase and carnitine dicarboxylyltransferase activities were detected in various tissues from untreated and clofibrate-treated rats with the exception of carnitine dodecanedioyltransferase reaction in livers from untreated and clofibrate-treated rats. In skeletal muscle, the acyl-CoA synthetase activities could be detected only in the presence of detergents.

Acyl Coenzyme A↗
PubMed1989

Rat liver metabolism of dicarboxylic acids.

Recently, we demonstrated in rat liver that dicarboxylic acids containing more than five carbons can be activated by a microsomal dicarboxylyl-CoA synthetase (J. Vamecq, E. de Hoffmann, and F. Van Hoof. Biochem. J. 230: 683-693, 1985). The products of this reaction, dicarboxylyl-CoA esters, were found to be substrates for an H2O2-generating dicarboxylyl-CoA oxidase. In the present work we report that 1) the catalytic center or the essential domains of dicarboxylyl-CoA synthetase are located at the cytosolic aspect of the endoplasmic reticulum membrane; 2) dicarboxylyl-CoA oxidase is optimally active on dodecanedioyl-CoA and is a peroxisomal enzyme; 3) cyanide-insensitive dodecanedioyl-CoA oxidation (NADH production) is catalyzed by rat liver homogenates. Cell fractionation studies disclose that, similar to dodecanedioyl-CoA oxidase (H2O2 production), the cyanide-insensitive dodecanedioyl-CoA oxidizing activity also belongs to peroxisomes; 4) a dodecanedioyl-CoA oxidoreductase reaction can be assayed by the dichlorphenolindophenol procedure in rat liver homogenates, and the activity is abundant in peroxisomal, mitochondrial, and soluble fractions; 5) by contrast with monocarboxylyl-CoA esters, the dicarboxylyl-CoAs are apparently not substrates for mitochondrial fatty acid oxidation; however, the use of dicarboxylylcarnitine esters as direct substrate for mitochondria suggests the existence of an active beta-oxidation of dicarboxylates in these organelles, which is further confirmed by experiments in which mitochondria are permeabilized with digitonin; 6) the in vivo oxidation of infused dodecanedioic acid results in a rapid appearance in urine of medium-chain dicarboxylic acids, with only 30-50% of the infused dose recovered in urine.

Acyl Coenzyme A↗
PubMed1989

Pathophysiology of peroxisomal beta-oxidation.

Mammalian peroxisomes are subcellular organelles involved in the metabolism of hydrogen peroxide (oxidases, catalase), lipid anabolism (ether lipid biosynthesis) and catabolism (oxidation of fatty acids and fatty acid derivatives), and intermediary metabolism (transaminases, dehydrogenases). Peroxisomes are formed by division, as is the case for mitochondria, but, in contrast to these organelles, they do not contain DNA. They were discovered and characterized (by biochemical and morphological techniques) later than the majority of the other cell components and specific procedures have been developed for their isolation. Functions of peroxisomes are, as a rule, shared by other cell compartments so that specific enzyme assays have also been developed. Combination of specific isolation procedures, enzyme assays and morphological analysis have resulted in our current knowledge of peroxisomal physiology which, however, has greatly benefited, as in the case of lysosomes, from the study of inborn errors of metabolism and the contribution of molecular biology. Novel enzymes and metabolic pathways have been demonstrated to exist in peroxisomes and human genetic disorders affecting one or several of these functions have been recognized.

Animals↗
PubMed1988

Comparison of the metabolism of dodecanedioic acid in vivo in control, riboflavin-deficient and clofibrate-treated rats.

Intravenous administration of dodecanedioate (or hexadecanedioate) to anaesthetized rats resulted in the urinary excretion of medium-chain dicarboxylic acids (adipic, suberic and sebacic acids). In control animals, the recovery of infused dodecanedioate in the form of urinary medium-chain dicarboxylic acids corresponded to 30% of the infused dose (22 mumol/100 g body mass). This excretion was markedly increased in riboflavin-deficient rats (75% of the infused dose) while it was severely decreased in clofibrate-treated animals (less than 5%). The initial velocity of this process was similar in both control and riboflavin-deficient rats. In control animals, halving the infused dose of dodecanedioate to 11 mumol/100 g body mass resulted in a halving of the initial rate of the urinary appearance of medium-chain dicarboxylates, while doubling the amount of dicarboxylate administered to 44 mumol/100 g body mass did not further modify this velocity, but rather prolonged the duration of the excretion of the resulting products. In riboflavin-deficient and clofibrate-treated rats, the hepatic peroxisomal dicarboxylyl-CoA beta-oxidation activity measured as dicarboxylyl-CoA H2O2-generating oxidase and cyanide-insensitive dicarboxylyl-CoA-dependent NAD+ reduction was increased about threefold and tenfold, respectively. Dicarboxylyl-CoA synthetase activity was normal in the clofibrate-treated rat livers but was increased more than tenfold in the livers from the riboflavin-deficient animals. This work provides evidence that in the rat both mitochondria and peroxisomes are involved in the catabolism of dicarboxylates.

Animals↗
PubMed1988

The enzymatic and mass spectrometric identification of 2-oxophytanic acid, a product of the peroxisomal oxidation of l-2-hydroxyphytanic acid.

A previously unreported metabolite of the mammalian phytanic acid breakdown pathway, 2-oxophytanic acid, was isolated and analysed by mass spectrometry. The metabolic origin of the 2-oxoacid is the oxidation by a rat kidney peroxisomal H2O2-generating oxidase of L-2-hydroxyphytanic acid, a well-established intermediate in phytanic acid alpha-oxidation.

Alcohol Oxidoreductases↗
PubMed1988

Beta-oxidation of the carboxyl side chain of prostaglandin E2 in rat liver peroxisomes and mitochondria.

Rat liver and kidney homogenates, fortified with the appropriate cofactors, produced H2O2 when incubated with prostaglandin (PG) E2 or its CoA ester (PGE2-CoA), indicating that PGE2-CoA served as substrate for acyl-CoA oxidase, the first enzyme of peroxisomal beta-oxidation. PGE2-CoA oxidase was stimulated to the same extent as palmitoyl-CoA oxidase by treatment of rats with the peroxisome proliferator clofibrate. Subcellular fractionation confirmed that both oxidase activities were located in peroxisomes. When highly purified peroxisomes were incubated with [1-14C]PGE2, radioactive oxidation products were released, demonstrating that peroxisomes were capable of catalyzing the complete beta-oxidation sequence. However, PGE2 beta-oxidizing activity was expressed only when isolated microsomes were added to the purified peroxisomes, indicating that PGE2-CoA synthetase is located in the endoplasmic reticulum. Cofactor requirements for peroxisomal [1-14C]PGE2 and [1-14C]palmitate oxidation were identical, and oxidation was not inhibited by cyanide. [1-14C]PGE2 was also beta-oxidized by highly purified mitochondrial fractions, devoid of peroxisomes, when microsomes were added. Mitochondrial [1-14C]PGE2 and [1-14C]palmitate oxidation was CoA- and ATP-dependent and inhibited by cyanide. Palmitate oxidation was carnitine-dependent, but PGE2 oxidation was not. Acyl-CoA dehydrogenase activity, but not carnitine acyltransferase activity, was detected with PGE2-CoA as substrate. [1-14C]PGE2 oxidation in whole liver homogenates was only slightly inhibited by cyanide, indicating that peroxisomes oxidized the major portion of PGE2. The concentrations of PGE2 employed in these experiments exceeded the in vivo concentrations by several orders of magnitude. Therefore, we suggest that the urinary PG metabolite excretion be measured in patients with hereditary diseases in which peroxisomal or mitochondrial beta-oxidation is not functioning in order to clarify the role of each organelle in PG oxidation in vivo.

Animals↗
PubMed1988

Polarizing inclusions in some organs of children with congenital peroxisomal diseases (Zellweger's, Refsum's, chondrodysplasia punctata (rhizomelic form), X-linked adrenoleukodystrophy).

Polarizing material has been reported in the liver of children with infantile Refsum's disease (IRD) and was absent in two patients with the cerebro-hepato-renal syndrome of Zellweger (CHRS). We examined in polarized light 15 liver biopsy and autopsy samples from six other patients with the cerebro-hepato-renal syndrome of Zellweger, two with the rhizomelic form of chondrodysplasia punctata (rCDP) and two with X-linked adrenoleukodystrophy (ALD), all conditions with deficient peroxisomes. Two types of birefringent inclusions were found in CHRS only: the first is transparent in bright field, the second appears as brown granules or rods, similar to lipofuscins. As in IRD large PAS-positive macrophage-like cells contain the transparent type. Electron microscopical investigation of these cells shows trilaminar structures within membrane-bound organelles. The two types were also seen in kidney and brown adipose tissue, the first type in pancreas, the second type in adrenal gland; no such was observed in myocardium or in thyroid gland (CHRS). No birefringent inclusions were present in rCDP and ALD. The nature of the inclusions is still unclear. An accumulation of the transparent polarizing material with increasing age of the patients is most likely.

Adipose Tissue, Brown↗
PubMed1988

A new peroxisomal disorder with enlarged peroxisomes and a specific deficiency of acyl-CoA oxidase (pseudo-neonatal adrenoleukodystrophy).

In the present paper two siblings are presented with clinical manifestations very similar to those of patients affected by neonatal adrenoleukodystrophy. In contrast to neonatal adrenoleukodystrophy patients, hepatic peroxisomes in these siblings were enlarged in size and not decreased in number. Accumulation of very-long-chain fatty acids (VLCFA) was associated with an isolated deficiency of the fatty acyl-CoA oxidase, the enzyme that catalyzes the first step of the peroxisomal beta-oxidation. Plasma levels of di- and trihydroxy-coprostanoic acid, phytanic acid, and pipecolic acid were normal; furthermore, acyl-CoA:dihydroxyacetone phosphate acyltransferase activity in cultured fibroblasts was also found to be normal. The clinical, biochemical, and cytochemical features found in these two siblings are compared with those seen in two other disorders characterized by the absence of a decreased number of hepatic peroxisomes and the presence of VLCFA: (1) pseudo-Zellweger syndrome (deficiency of peroxisomal thiolase activity) and (2) X-linked childhood adrenoleukodystrophy (deficiency of activation of lignoceric acid). Review of the different biochemical defects possible in very-long-chain fatty-acid oxidation reveals different clinical pictures of varying severity, depending on the level at which the biochemical defect occurs.

Acetyl-CoA C-Acetyltransferase↗