Marie-Françoise Vincent

Inhibition of fatty acid and cholesterol synthesis by stimulation of AMP-activated protein kinase.

AMP‐activated protein kinase is a multisubstrate protein kinase that, in liver, inactivates both acetyl‐CoA carboxylase, the rate‐limiting enzyme of fatty acid synthesis, and 3‐hydroxy‐3‐methyl‐glutaryl‐CoA reductase, the rate‐limiting enzyme of cholesterol synthesis. AICAR (5‐amino 4‐imidazolecarboxamide ribotide, ZMP) was found to stimulate up to 10‐fold rat liver AMP‐activated protein kinase, with a half‐maximal effect at approximately 5 mM. In accordance with previous observations, addition to suspensions of isolated rat hepatocytes of 50–500 μM AICAriboside, the nucleoside corresponding to ZMP, resulted in the accumulation of millimolar concentrations of the latter. This was accompanied by a dose‐dependent inactivation of both acetyl‐CoA carboxylase and 3‐hydroxy‐3‐methylglutaryl‐CoA reductase. Addition of 50–500 μM AICAriboside to hepatocyte suspensions incubated in the presence of various substrates, including glucose and lactate/pyruvate, caused a parallel inhibition of both fatty acid and cholesterol synthesis. With lactate/pyruvate (10/1 mM), half‐maximal inhibition was obtained at approximately 100 μM, and near‐complete inhibition at 500 μM AI‐CAriboside. These findings open new perspectives for the simultaneous control of triglyceride and cholesterol synthesis by pharmacological stimulators of AMP‐activated protein kinase.—Henin, N., Vincent, M.‐F., Gruber, H. E., Van den Berghe, G. Inhibition of fatty acid and cholesterol synthesis by stimulation of AMP‐activated protein kinase. FASEB J. 9, 541–546 (1995)

Hepatocyte transplantation in a 4-year-old girl with peroxisomal biogenesis disease: technique, safety, and metabolic follow-up.

Hepatocyte transplantation is an investigational alternative to orthotopic liver transplantation to treat liver based inborn errors of metabolism. We report successful hepatocyte transplantation in a 4-year-old girl with infantile Refsum disease. Hepatocytes were isolated from the left liver segment of two male donors using a classic two-step perfusion method. Fresh cells were transplanted first and then cryopreserved cells, for a total of 2 billion cells. Total bile acids and abnormal dihydroxycoprostanoïc acid markedly decreased in the patients serum, indicating resolution of cholestasis and re-population of liver cells. Pipecholic acid decreased by 40% and c26:c22 fatty acid ratio by 36% after 18 months. Donor chromosomes sequences were detected on biopsy posttransplant, indicating engraftment. Hepatocyte transplantation is a safe and promising technique in the treatment of rare inborn errors of metabolism. Future improvements of cell viability and prevention of apoptosis may increase engraftment and subsequent re-population.

Molecular analysis of MVK mutations and enzymatic activity in hyper-IgD and periodic fever syndrome

Hyperimmunoglobulinaemia D and periodic fever syndrome (HIDS) is an autosomal recessive inflammatory disorder characterised by recurrent episode of fever associated with lymphadenopathy, abdominal distress, joint involvement and skin lesions. We recently demonstrated that mutations in the mevalonate kinase gene (MVK) are associated with HIDS. Direct DNA sequencing was done to screen the entire coding region of MVK in 25 unrelated patients with HIDS. Mutations were detected in the coding region of the gene including 11 missense mutations, one deletion, the absence of expression of one allele, as well as three novel polymorphisms. Seven of these mutations are novel. The large majority of the patients were compound heterozygotes for two mutations. Of these, V377I (G→A) is the most common mutation occurring in 20 unrelated patients and was found to be associated with I268T in six patients. Mutations were associated with a decrease of mevalonate kinase (MK) (ATP:mevalonate 5-phosphotransferase, EC 2.7.I.36) enzymatic activity but not as profound as in mevalonic aciduria, a syndrome also caused by a deficient activity of MK. In HIDS the mutations are located all along the protein which is different from mevalonic aciduria where MK mutations are mainly clustered to a same region of the protein. On the basis of this study, we propose that the diagnostic screen of MVK in HIDS should be first directed on V377I and I268T mutations. Three patients are also described to illustrate the genotypic and phenotypic overlap with mevalonic aciduria.

Adenylosuccinase Deficiency - An Inborn Error of Purine Nucleotide Synthesis

Clinical and biochemical data are presented on eight children with adenylosuccinase deficiency. This newly discovered inborn error of purine metabolism is characterized by an accumulation in body fluids of succinyladenosine (S-Ado) and succinylaminoimidazole carboxamide riboside (SAICA riboside), the dephosphorylated derivatives of the two substrates of adenylosuccinase. Six living children (three boys and three girls) and one deceased sibling displayed severe psychomotor retardation. Epilepsy was documented in five cases, autistic features in three, and growth retardation associated with muscular wasting in a brother and sister. In the cerebrospinal fluid, plasma and urine of these patients, the S-Ado/SAICA riboside ratio was between 1 and 2. In striking contrast, the eighth patient (a girl) was markedly less mentally retarded. Most noteworthy, the S-Ado/SAICA riboside ratio in her body fluids was around 5, suggesting that her milder psychomotor retardation was causally linked to this higher ratio. Adenylosuccinase deficiency was demonstrated in the liver of all seven living children, in the kidney of three patients in whom the enzymatic activity was measured, and in the muscle of three patients, including the two with muscular wasting. In fibroblasts of the six severely retarded patients, adenylosuccinase activity was reduced to approximately 40% of normal; in the patient with the higher S-Ado/SAICA riboside ratio, it reached only 6% of normal. The clinical heterogeneity of adenylosuccinase deficiency justifies systematic screening for the enzyme defect in unexplained neurological disease.

Molecular identification of aspartate N-acetyltransferase and its mutation in hypoacetylaspartia

The brain-specific compound NAA (N-acetylaspartate) occurs almost exclusively in neurons, where its concentration reaches approx. 20 mM. Its abundance is determined in patients by MRS (magnetic resonance spectroscopy) to assess neuronal density and health. The molecular identity of the NAT (N-acetyltransferase) that catalyses NAA synthesis has remained unknown, because the enzyme is membrane-bound and difficult to purify. Database searches indicated that among putative NATs (i.e. proteins homologous with known NATs, but with uncharacterized catalytic activity) encoded by the human and mouse genomes two were almost exclusively expressed in brain, NAT8L and NAT14. Transfection studies in HEK-293T [human embryonic kidney-293 cells expressing the large T-antigen of SV40 (simian virus 40)] indicated that NAT8L, but not NAT14, catalysed the synthesis of NAA from L-aspartate and acetyl-CoA. The specificity of NAT8L, its Km for aspartate and its sensitivity to detergents are similar to those described for brain Asp-NAT. Confocal microscopy analysis of CHO (Chinese-hamster ovary) cells and neurons expressing recombinant NAT8L indicates that it is associated with the ER (endoplasmic reticulum), but not with mitochondria. A mutation search in the NAT8L gene of the only patient known to be deficient in NAA disclosed the presence of a homozygous 19 bp deletion, resulting in a change in reading frame and the absence of production of a functional protein. We conclude that NAT8L, a neuron-specific protein, is responsible for NAA synthesis and is mutated in primary NAA deficiency (hypoacetylaspartia). The molecular identification of this enzyme will lead to new perspectives in the clarification of the function of this most abundant amino acid derivative in neurons and for the diagnosis of hypoacetylaspartia in other patients.

Hypoglycaemic effect of AICAriboside in mice

SummaryWe have previously demonstrated that in isolated hepatocytes from fasted rats, AICAriboside (5-amino 4-imidazolecarboxamide riboside), after its conversion into AICAribotide (AICAR or ZMP), exerts a dose-dependent inhibition on fructose-1,6-bisphosphatase and hence on gluconeogenesis. To assess the effect of AICAriboside in vivo, we measured plasma glucose and liver metabolites after intraperitoneal administration of AICAriboside in mice. In fasted animals, in which gluconeogenesis is activated, AICAriboside (250 mg/kg body weight) induced a 50% decrease of plasma glucose within 15 min, which lasted about 3 h. In fed mice, glucose decreased by 8% at 30 min, and normalized at 1 h. Under both conditions, ZMP accumulated to approximately 2 µmol/g of liver at 1 h. It decreased progressively thereafter, although much more slowly in the fasted state. Inhibition of fructose-1,6-bisphosphatase was evidenced by time-wise linear accumulations of fructose-1,6-bisphosphate, from 0.006 to 3.9 µmol/g of liver at 3 h in fasted mice, and from 0.010 to 0.114 µmol/g of liver at 1 h in fed animals. AICAriboside did not significantly influence plasma insulin or glucose utilization by muscle. We conclude that in vivo as in isolated hepatocytes, AICAriboside, owing to its conversion into ZMP, inhibits fructose-1,6-bisphosphatase and consequently gluconeogenesis.

l-2-Hydroxyglutaric aciduria, a defect of metabolite repair

Summaryl-2-hydroxyglutaric aciduria is a metabolic disorder in which l-2-hydroxyglutarate accumulates as a result of a deficiency in FAD-linked l-2-hydroxyglutarate dehydrogenase, a mitochondrial enzyme converting l-2-hydroxyglutarate to α-ketoglutarate. The origin of the l-2-hydroxyglutarate, which accumulates in this disorder, is presently unknown. The oxidation–reduction potential of the 2-hydroxyglutarate/α-ketoglutarate couple is such that l-2-hydroxyglutarate could potentially be produced through the reduction of α-ketoglutarate by a NAD- or NADP-linked oxidoreductase. In fractions of rat liver cytosolic extracts that had been chromatographed on an anion exchanger we detected an enzyme reducing α-ketoglutarate in the presence of NADH. This enzyme co-purified with cytosolic l-malate dehydrogenase (cMDH) upon further chromatography on Blue Sepharose. Mitochondrial fractions also contained an NADH-linked, ‘α-ketoglutarate reductase’ which similarly co-purified with mitochondrial l-malate dehydrogenase (mMDH). Purified mMDH catalysed the reduction of α-ketoglutarate to l-2-hydroxyglutarate with a catalytic efficiency that was about 107-fold lower than that observed with oxaloacetate. For the cytosolic enzyme, this ratio amounted to 108, indicating that this enzyme is more specific. Both cMDH and mMDH are highly active in tissues and α-ketoglutarate is much more abundant than oxaloacetate and more concentrated in mitochondria than in the cytosol. As a result of this, the weak activity of mMDH on α-ketoglutarate is sufficient to account for the amount of l-2-hydroxyglutarate that is excreted by patients deficient in FAD-linked l-2-hydroxyglutarate dehydrogenase. The latter enzyme appears, therefore, to be responsible for a ‘metabolite repair’ phenomenon and to belong to the expanding class of ‘house-cleaning’ enzymes.

Inborn errors of the purine nucleotide cycle: adenylosuccinase deficiency.

Adenylosuccinase catalyses two reactions in purine metabolism: the conversion of succinylaminoimidazole carboxamide ribotide (SAICAR) into amino-imidazole carboxamide ribotide (AICAR) along the de novo synthesis of purine nucleotides, and the conversion of adenylosuccinate (S-AMP) into AMP in the conversion of IMP into AMP. The hallmarks of adenylosuccinase deficiency are the presence of succinylaminoimidazole carboxamide riboside (SAICAriboside) and succinyladenosine (S-Ado) in body fluids. These normally undetectable succinyl-purines are the products of the dephosphorylation, by cytosolic 5′-nucleotidase, of the two substrates of adenylosuccinase. The clinical picture of the enzyme deficiency is markedly heterogeneous with, as a rule, a profound, but nevertheless variable degree of psychomotor delay, often convulsions and/or autistic features, sometimes growth retardation and muscular dystrophy. The diagnostic tests that can be used for diagnosis, the enzyme and gene defects that have been identified, and the hypotheses that have been put forward to explain the pathophysiology of the disorder are reviewed.

Effects of a Cardioselective Beta-1 Partial Agonist (corwin) On Left-ventricular Function and Myocardial-metabolism in Patients With Previous Myocardial-infarction

Corwin is a new selective beta 1 partial agonist, able to stabilize the beta 1 adrenoceptors at approximately 43% of their maximal activity. The aim of the study was to determine the effects of this agent in patients with coronary artery disease (CAD) and previous myocardial infarction (MI). In a first group of 14 patients, corwin increased significantly the peak (+)dP/dt (+35%; p less than 0.005), the global ejection fraction, and the ejection fraction of abnormally contracting segments (from 20 +/- 18 to 26 +/- 19%; p less than 0.02). Corwin also induced significant decreases in mean systolic (-8%; p less than 0.05) and mean diastolic (-38%; p less than 0.001) wall stress and accelerated the relaxation rate. In a second group of 11 patients, a metabolic study indicated that neither myocardial oxygen consumption (15 +/- 7 versus 15 +/- 7 ml/min; difference not significant) nor lactate extraction was modified by the drug. In this group, increases in peak (+)dP/dt, acceleration in ventricular relaxation (-8 ms in time constant of isovolumic pressure decrease; p less than 0.01), and decreases in left ventricular end-diastolic pressure also were noted after administration of corwin, both under basal conditions and during a cold pressor test. In conclusion, corwin is a positive inotrope which, in patients with CAD and left ventricular dysfunction, improves left ventricular systolic and diastolic function without inducing myocardial ischemia.

Effects of Nicardipine and Nisoldipine on Myocardial Metabolism, Coronary Blood Flow and Oxygen Supply in Angina Pectoris

The effects of the calcium antagonists nicardipine and nisoldipine on left ventricular (LV) metabolism were analyzed in 32 patients with angina pectoris. Measurements were made at a fixed heart rate under the basal state and during a cold pressor test (CPT). After administration of the drugs, coronary blood flow increased significantly and the mean aortic pressure decreased by 10% (p less than 0.01) in the basal state and by 11% (p less than 0.01) during CPT. Despite the reduction in pressure-rate product, myocardial oxygen consumption was unchanged in the basal state (18 +/- 4 vs 19 +/- 4 ml/min, difference not significant) and during CPT (21 +/- 5 vs 21 +/- 5 ml/min, difference not significant); this discrepancy between a reduced pressure-rate product and an unchanged oxygen consumption was also noted when nicardipine was given after propranolol (0.1 mg/kg; 12 patients). Both agents also increased LV lactate uptake, particularly during CPT (+13 mumol/min, p less than 0.05 vs control CPT) and reduced LV glutamine production. In 10 patients in whom 14C-lactate was infused, the chemical LV lactate extraction ratio increased more than the 14C-lactate extraction ratio after administration of the drugs, indicating a reduction in LV lactate production. The data are consistent with the hypothesis that nicardipine and nisoldipine improve perfusion and aerobic metabolism in chronically ischemic areas, resulting in an augmented oxygen consumption and in a reduced lactate production.