Effect of diphenylhydantoin on protein metabolism in the central nervous system. Study of subcellular fractions

Paraneoplastic cerebellar degeneration with a circulating antibody against neurons and non-neuronal cells

We describe a woman with paraneoplastic cerebellar degeneration associated with para-ovarian adenocarcinoma, who had a circulating antibody with a corresponding antigen not only in cerebellar Purkinje cells but also in neurons located in the molecular layer of the human and rat cerebellum. The antigen was also present in neurons in the cerebral cortex, brain stem, anterior horn cells, dorsal root ganglia, intestinal autonomic neurons, retinal ganglion cells, Schwann cells of the peripheral nerve and epithelial cells of the renal glomerulus in rats. Immunoelectron microscopy revealed immunoprecipitates in the smooth and rough endoplasmic reticulum and polyribosomes in human and rat cerebellar Purkinje cells and other neuronal cell bodies as well as Schwann cells of the peripheral nerve. Even though patients with this disorder manifest primarily with cerebellar and some extracerebellar signs, the antigen also exists in many neurons other than cerebellar Purkinje cells and even in non-neuronal cells. The clinicopathologic significance of the observed immunologic reaction in diverse neurons remains to be determined.

Axonal dystrophy in the posterior column nuclei of young adult epileptics with chronic phenytoin intoxication

Axonal spheroids in the posterior column nuclei of phenytoin-intoxicated epileptics were classified according to their predominant subcellular components into six types, and their incidences were compared with those in controls. Spheroids from phenytoin-intoxicated epileptics showed significantly higher proportions of the tubulomembranous (TM) and layered membrane loop (LML) types in the gracile nucleus, appearance of the same types in the cuneate nucleus, and a significant decrease of the neurofilamentous (NF) type in both nuclei. The incidences of the complex body (CB) and granular material types and of the homogeneous dense-body (HDB) type, which appeared only in the gracile nucleus, showed no difference between the intoxicated patients and the controls. The NF, CB and HDB types were therefore considered to be nonspecific. It was thought that chronic phenytoin intoxication might induce dystrophic changes, such as those characterized by the presence of the TM and LML types, in the axon terminals of the gracile and cuneate nuclei, possibly due to some abnormalities of the axoplasmic transport system.

Effect of phenytoin on human cerebral glucose metabolism

We used serial positron emission tomography scans with [18F]2-deoxyglucose to study the effect of phenytoin on human cerebral glucose metabolism in 10 patients with seizure disorders. Local CMRglu for each patient was measured in 10 regions of interest. EEGs were performed during each procedure to match scans for state of consciousness and exclude data from scans with ictal activity. Serial scans without a drug change were performed in six control patients. Metabolic rates were significantly lower in two cortical regions while patients were taking phenytoin. No significant changes on repeat scan were seen in the control population. Measured across all regions of interest, metabolic rates were 13% higher when patients were off phenytoin (p less than 0.02).

Differential inhibition of protein synthesis: a possible biochemical mechanism of thalidomide teratogenesis

A theory concerning the chemical and biochemical mechanisms of thalidomide teratogenesis is presented. A considerable body of evidence suggests that the glutarimide ring of thalidomide may exert its biological activity because of its resemblance to the imide pyrimidines thymine and uracil. In addition to the glutarimide ring, thalidomide contains a moderately reactive phthalimide moiety, which allows the spontaneous formation of various glutarimide derivatives in fetal tissues. A model is proposed in which the phthalimide group reacts with small nucleophiles, most likely the polyamines, to produce a derivative(s) having a similar biochemical potential to that of cycloheximide, a glutarimide which is a powerful inhibitor of the elongation phase of protein synthesis. Interference in the elongation phase results in the selective inhibition of the translation of messages which have a high translational efficiency. Evidence is reviewed concerning the differential inhibition or protein synthesis by cycloheximide and the effects of this inhibition on various biochemical and biological processes which are critical during development and differentiation. A similar biochemical activity by the putative thalidomide derivative(s) could explain its extreme teratogenic potential. A number of parallels between the biological effects of thalidomide and cycloheximide are discussed which support the idea that a similar biochemical activity is involved. The theory readily explains many of the observed biological effects of thalidomide including the large difference between fetal and adult toxicity. In addition, evidence is reviewed which suggests that the teratogenic properties of a number of drugs which are structurally related to thalidomide may have a common chemical basis due to the similarity of their imide core structures to thymine and uracil.

Brain maturation following administration of phenobarbital, phenytoin, and sodium valproate to developing rats or to their dams: effects on synthesis of brain myelin and other subcellular membrane proteins

The anticonvulsant drugs phenobarbital, phenytoin, sodium valproate, and phenytoin-sodium valproate in combination were administered daily to (a) pregnant rats starting on the 5th day after conception, and continued through 17 days postpartum, or (b) to developing rats between 3 and 17 days of age. Each drug was prepared in water and administered at either a therapeutic dose (TD), three times therapeutic dose (3TD), or 9TD. Drug administration had no discernible effect on litter size or sex ratio in the offspring; however, phenobarbital administration to dams caused small but significant reductions in birth weights. Body weights of developing rats treated with anticonvulsant drugs either via dams of directly by intraperitoneal injection lagged behind controls. At 20-24 days of age the brain weights of the offspring of phenobarbital (9TD)-exposed dams lagged control weights by 5% whereas brain weights in the offspring of the other treated groups were indistinguishable from controls. In contrast, administration of phenobarbital directly to developing rats caused no significant brain weight deficits whereas significant deficits were observed with phenytoin (9TD), sodium valproate (9TD), and phenytoin-sodium valproate (9TD) in combination. AT 20-24 days of age the relative incorporation of radioactive leucine into purified myelin and crude nuclear proteins of drug-treated rats or the offspring of drug-treated dams was reduced by 10-20% in all cases. Dose-related differences were not observed however, and the effects of phenytoin and sodium valproate in combination approximated those of phenytoin administered alone.

A method for large-scale production of mouse brain cortical cultures

Fetal cerebral cortex can be grown for several weeks in dissociated cell culture using a relatively simple protocol for culture preparation. It is possible to establish large numbers of very similar cultures which serve as an effective test system for studies of toxicity and mechanism of action of neuroactive compounds. Light microscopic and ultrastructural studies document the neuronal component of the cultures as well as the developmental sequence. Cell counts, protein concentration and choline acetyltransferase activity demonstrate the reproducibility of the cultures from dish to dish.

Effects of cyclic analogs of GABA on protein synthesis and discrimination learning

Three cyclic analogs of gamma-aminobutyric acid (GABA)-5-ethyl, 5-phenyl, 2-pyrrolidinone (EPP), 5-diphenyl, 2-pyrrolidinone (DPP), and 5-methyl, 5-phenyl, 2-pyrrolidinone (MPP)- were studied in relation to protein synthesis and the latter in relation to discrimination learning. The present study shows that when different groups of rats were injected subcutaneously with 10 mg/kg of EPP or DPP, the protein synthesis in vitro was inhibited 75% in brain mitochondria. MPP at the same doses was the less potent inhibitor of mitochondria protein synthesis. Experiments on discrimination learning show that 10mg/kg of MPP enhance the response decision speed in presence of S(+) (white arm) and S(-) (black arm).

Effects of anticonvulsant drugs on the synthesis of DNA and protein by human bone marrow cells in vitro

Suspensions of human bone marrow cells were incubated with various concentrations of phenobarbitone or phenytoin sodium for 2 h, and the effects of this incubation on the subsequent incorporation of 3H-thymidine and3H-leucine into DNA and protein, respectively, were studied. Both drugs caused a depression of 3H-thymidine incorporation and this phenomenon was not prevented by the addition of 100 mug of pteroyl-glutamic acid, folinic acid or 5-methyltetrahydrofolate per ml of marrow culture. The lowest concentration of drug which caused a statistically significant depression of 3H-thymidine incorporation was 200 mug per ml for phenobarbitone and 50 mug per ml for phenytoin sodium. Both phenobarbitone and phenytoin sodium also caused an increase in the incorporation of 3H-leucine at concentrations of 50 and 20 mug per ml, respectively, suggesting the possibility that a stimulation of protein synthesis within erythropoietic cells may play an important role in the development of anticonvulsant-induced macrocytosis.

Optimal conditions for protein synthesis in incubated slices of rat brain

Optimal conditions for protein synthesis in incubated slices of rat brain were determined to be: thickness 0.3 mm under air (for newborn 0.4-0.6 mm) or 0.5 mm under oxygen; temperature, 35-36 degrees C; hepes (N-2-hydroxyethylpiperazine-N'-2-ethane sulfonic acid) buffer; K+, 6-8 mM; Ca2+, 2-3 mM. Though maximum incorporation was found with a Na+ concentration of 110-12- mM. Though maximum incorporation was found with a Na+ concentration of 110-120mM, this requirement appears to be partly osmotic. The Na+ concentration may be reduced to 80 mM without inhibition of incorporation provided adjustment is made for osmotic balance. Mg2+. Optimal pH was 7.2-7.4. The rate of protein synthesis in this medium is 0.08-0.09% replacement of the protein amino acid/h in slices from adults and 1.6%/h in slices from 3-day-old rats. Thus slices from adults synthesize protein at 10-20% of the in vivo rate whereas slices at 3-day-old brainincorporate amino acid at 70-80% of the in vivo rate for young rats.

Effect of anoxia on protein metabolism in subcellular fractions of rabbit brain

The effect of cerebral anoxia on leucine incorporation into proteins of various subcellular fractions from rabbit brain was studied by using a previously reported in vitro model. Although the decrease in leucine incorporation was observed earlier in nuclei and microsomes, other fractions also demonstrated a rapid decrease. These results were quite different from the pattern of leucine incorporation observed in a type of reversible suppression produced with diphenylhydantoin.