J. P. Nuyts

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.

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.

CoA esters of valproic acid and related metabolites are oxidized in peroxisomes through a pathway distinct from peroxisomal fatty and bile acyl-CoA β-oxidation

In rat liver homogenates fortified with the appropriate cofactors (ATP and CoA), valproic acid induced H2O2 production rates by far lower than those recorded on the straight medium‐chain fatty acid n‐octanoic acid. Using directly the CoA esters of these carboxylic acids as substrates for the rat liver H2O2‐generating enzyme activities, valproyl‐CoA, and n‐octanoyl‐CoA were found to induce similar oxidation rates. In the rat liver homogenates, cyanide‐insensitive valproyl‐CoA and octanoyl‐CoA oxidations occurred at rates similar to those of valproyl‐CoA and octanoyl‐CoA oxidase(s), respectively. Studies on fractions obtained from rat liver postnuclear supernatants by isopycnic centrifugation on a linear sucrose density gradient disclose that the density distribution of valproyl‐CoA oxidase superimposes to those of catalase, fatty acyl‐CoA oxidase and cyanide‐insensitive fatty acyl‐CoA oxidation, three peroxisomal marker activities. By contrast, the cyanide‐insensitive valproyl‐CoA oxidation does not adopt the typical peroxisomal distribution of these activities but rather exhibits a mitochondrial localization with, however, a minor peroxisomal component. Interestingly enough, the comparative study of rat tissue distribution, inducibility by clofibrate and sensitivity to deoxycholate indicated that valproyl‐CoA oxidase is an enzyme distinct from fatty acyl‐CoA oxidase and bile acyl‐CoA oxidase. Taken as a whole, the results presented here support the occurrence of a peroxisomal oxidation of the CoA ester of valproic acid and its Δ4‐enoic derivate which might be characterized by two major features: initiation by an acyl‐CoA oxidase distinct from fatty and bile acyl‐CoA oxidases, and inability to complete the β‐oxidation cycle which would not proceed, at significant rates, further than the β‐hydroxyacyl‐CoA dehydrogenation step in peroxisomes.

Preliminary studies about novel strategies to reverse chemoresistance to adriamycin regarding glutathione metabolism, peroxisomal and extraperoxisomal hydroperoxide and valproic acid metabolic pathways

Summary— The present work was aimed at defining novel strategies to reverse chemoresistance to anticancer drugs, especially by interfering with cellular glutathione metabolism, peroxisomal and/or extraperoxisomal hydroperoxide metabolic pathways. Preliminary results are presented about molecules we demonstrated to be capable of interfering with hydrogen peroxide metabolism in cells. Prior to describing these molecules, a short overview of glutathione and free radical metabolic pathways is presented as well as a rapid presentation of the characteristics of chemo‐sensitivity and ‐resistance towards the anticancer drug adriamycin, with special emphasis on hydrogen peroxide metabolism. The strategies currently developed to reverse chemoresistance are further presented. in subsequent sections, our own strategy to achieve inhibition of hydrogen peroxide breakdown and stimulation of peroxisomal hydrogen peroxide production is illustrated on the basis of molecular modelling studies and biochemical investigations on extraperoxisomal and peroxisomal metabolic pathways. Preliminary studies on cultured cells have been initiated. The perspective for future studies is presented as well as other possible models of chemoresistance as target for the design of hydrogen peroxide metabolism‐interfering pharmacomolecules.