The effects of anticonvulsants on in vitro protein synthesis in immature brain

Influence of phenytoin on cytoskeletal organization and cell viability of immortalized mouse hippocampal neurons

Phenytoin (PHT) is a commonly used anticonvulsant drug; several side effects have been described, including morphological changes in brain cortex and cerebellar neurons and teratogenic lesions in infants of epileptic mothers. Evidence of other authors indicate that PHT may exert its action through the modification of phosphorylation patterns of cytoskeletal polypeptides. We have studied the influence of the anticonvulsant drug phenytoin on immortalized mouse hippocampal neurons in culture. This was done by means of MTT-assays, immunocytochemical and immunoblot analyses, measurements of cell metabolism, measurements of the length of neuronal processes, and electron microscopy. A distinct and pronounced effect of PHT could be characterized with regard to the formation of neuronal processes, involving malfunction of an assembly-mechanism of cytoskeletal constituents. These accumulated within appendages (blebs) or cytoplasmic condensations, instead of forming normally organized processes. However, PHT did not interfere with bulk synthesis of cell proteins and specific cytoskeletal components.

Applications of molecular physics ‘biotechnology’ to the rational design of an improved phenytoin analogue

This study exploits molecular physics, in conjunction with a large scale computing environment, as a tool for understanding the clinical phenomenology of phenytoin (PHT) toxicology at a molecular level and for employing this understanding in an attempt to design improved drugs. The application of molecular physics techniques, such as quantum mechanics and molecular force field calculations, to the process of rational anticonvulsant drug design remains virtually unexplored. A 3-step strategy for applying these techniques to the design of an improved PHT molecule is presented. Step 1 employs quantitative structure-activity relationship calculations on 80 PHT analogues to ascertain the portion of the PHT molecule necessary for bioactivity (i.e. the 'bioactive face' of PHT); the N3-C4(O)-C5-R fragment of PHT was identified as the bioactive face. Step 2 employs molecular modelling studies to determine the portion of the PHT molecule necessary for the teratogenic, mutagenic and connective tissue toxicities of PHT (i.e. the 'biotoxic face'); the C2(O)-N3 fragment of PHT was identified as the biotoxic face. Step 3 experiments design an 'improved' PHT analogue, which maintains the bioactive face while eliminating the integrity of the biotoxic face; 2-deoxy-5,5-diphenylhydantoin was designed and synthesized as the improved PHT analogue. This compound had biological activity equivalent to PHT, but was unable to bind to nucleic acids or to chelate metals involved in connective tissue metabolism.

Effects of phenobarbital and phenytoin on cortical glial cells in culture

Studies were undertaken to determine the effects of 7-day phenobarbital and phenytoin exposure on 14-day-old glial cell cultures of fetal murine cortex. Biochemical markers monitored were Ro5-4684-displaceable 3H-flunitrazepam binding, 3H-beta-alanine uptake, glutamine synthetase activity, and protein content. Phenobarbital concentrations were 30, 60, and 120 micrograms/ml and phenytoin concentrations 15, 30, 60 micrograms/ml. There were no discernible phase microscopic changes at any concentration of either drug. Phenobarbital produced no significant changes in the biochemical measures monitored. Exposure to phenytoin produced no biochemical changes at 15 micrograms/ml, but did produce significant changes at 30 and 60 micrograms/ml. There was an increase in Ro5-4684-displaceable 3H-flunitrazepam binding signifying increased binding or an increase in the number of binding sites and perhaps an increased population of glial cells although, the unchanged protein content suggests that the number of glial cells was not increased. There was a decrease with 30 and 60 micrograms/ml phenytoin of 3H-beta-alanine uptake suggesting interference with normal membrane transport of this compound. The latter effect may well mirror changes in GABA uptake in glial cells in the presence of phenytoin.

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).

Degeneration of granule cells following chronic phenytoin administration: an electron microscopic investigation of the mouse cerebellum

Fifteen male mice (C57/Bl6J) were fed the liquid diet "Stardit" supplemented with vitamins together with phenytoin for 8 weeks; experimental animals and controls were pair-fed. After 8 weeks of treatment, the anesthetized animals were perfused with 3.5% glutaraldehyde. Tissue samples of the cerebral cortex (area 3), cerebellum (vermis), thalamus, hypothalamus, and liver were embedded in Araldite. All phenytoin-treated animals displayed a hepatomegaly. Semithin sections and ultrastructural investigations of the cerebellar vermis showed pyknoses of granule cells and an enlargement and swelling of parallel fibers in presynaptic areas in the molecular layer. The swollen axons showed an accumulation of tubular structures which represented proliferated smooth endoplasmic reticulum. Similar tubular structures were observed in hepatocytes of experimental animals. It is proposed that phenytoin caused an induction of the microsomal system of hepatocytes and granule cells which led to a proliferation of the smooth endoplasmic reticulum. The transport of these organelles to the axon terminals of parallel fibers via the axoplasmic flow is assumed to cause a swelling of the presynaptic area. A dying-back process may then lead to pyknosis of granule cells. Chronic phenytoin administration to mice is a new experimental model of neuroaxonal dystrophy.

Damage of Purkinje cell axons following chronic phenytoin administration: an animal model of distal axonopathy

An animal model of central distal axonopathy following chronic administration of phenytoin is described. Male C57/BL6J mice received diphenylhydantoin (DPH) in the daily diet (liquid diet 'Stardit', supplemented with vitamins) over a period of 8 weeks. Control and experimental animals were pair-fed. Twelve mice of both groups were perfused via the left ventricle with glutaraldehyde. Representative samples of the cerebral cortex (area 3), cerebellum (vermis and deep cerebellar nuclei), thalamus, hypothalamus, and liver were embedded in araldite. Semi-thin sections and electron microscopy of the cerebellar vermis revealed marked dystrophic changes in the Purkinje cell axons. The presynaptic segments of Purkinje cell axons in the deep cerebellar nuclei showed massive enlargement and swelling due to accumulation of spherical particles and tubular structures in the axoplasm. These structures represent a proliferation of the smooth endoplasmic reticulum. Identical changes were found in hepatocytes of treated animals. Because phenytoin induces hepatic microsomal enzymes, we suggest that phenytoin-related Purkinje cell damage may be produced by an induction of Purkinje cell microsomes with proliferation of the smooth endoplasmic reticulum which causes a swelling and enlargement of presynaptic segments of Purkinje cell axons in deep cerebellar nuclei. Chronic phenytoin administration to mice is a new model of phenytoin-induced encephalopathy and of distal axonopathy of cerebellar neurons.

Phencyclidine and analogues: effects on brain protein synthesis

Phencyclidine and four analogues were tested for their capacity to inhibit total protein synthesis in a brain homogenate. At 1.0 mM they were all found to be potent inhibitors with values ranging from 36% to 96% inhibition. At this high concentration two of the analogues were equal to or more effective than the classic protein synthesis inhibitors cycloheximide and emetine. At lower concentrations the inhibition dropped off sharply to 18% at 1.0 X 10(-4) M and 9% at 1.0 X 10(-5) M for phencyclidine. If the inhibition observed in the brain homogenate occurs in vivo it may account for the high incidence of memory loss reported with phencyclidine use.

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.

Adverse effects of phenobarbital on morphological and biochemical development of fetal mouse spinal cord neurons in culture

The effects of chronic phenobarbital treatment on neuronal development were assessed in cell cultures of fetal rodent spinal cord. The activity of the principal enzyme involved in acetylcholine synthesis, choline acetyltransferase (CAT), and counts of large spinal cord neurons were used as indicators of neuronal development Phenobarbital (30 to 120 micrograms/ml) added to cultures for two- or six-week periods produced dose-dependent decreases in both CAT activity and neurons counts. Barbituric acid at doses equimolar to those at which phenobarbital produced these decreases had no effect.

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.