Binding of diphenylhydantoin to brain protein

Relationship between ischemic damage and concentrations of phenytoin and phenobarbital in the brain cortex of epileptic patients in vegetative state at death

Post-mortem concentrations of phenytoin (PHT) and phenobarbital (PB) were determined by high-performance liquid chromatography in the cortical matter of specified brain regions and in the serum (total and free) from 3 epileptic males in vegetative state and compared to the data of 45 deceased epileptic control patients. The duration of the vegetative state was 12 days, 15 days or about 4 months until death and was associated with corresponding stages of generalized ischemic brain damage. The histological examination was completed by immunohistochemical and morphometric methods. According to other investigators nerve cells are the major binding sites for PHT and PB in the cerebral cortex of rodents. But, in the 3 comatose patients the PHT and PB concentrations of the isocortex and neocerebellum were not significantly decreased in comparison with the control patients despite necrosis and loss of neurons as well as other distinct tissue alterations. The results strongly favor the non-specific binding of PHT and PB to cells and subcellular structures of the brain-mainly based on simple physico-chemical principles.

Lack of effect of histological lesions on the phenytoin and phenobarbital concentrations in the brain cortex of epileptic patients

Postmortem concentrations of phenytoin (PHT) and phenobarbital (PB) were determined in 24 specimens of the frontal, temporal, occipital or neocerebellar cortex with different pathological changes and in the serum (total and free) from 11 epileptic patients. The cortical lesions were characterized by various degrees of neuronal loss or necrosis associated with other changes such as proliferated gliocytes, fibre gliosis, Rosenthal fibres or numerous corpora amylacea. According to other investigators neurons are the main binding sites of PHT and PB in rodent brains. The PHT and PB concentrations in 20 cortical lesions from nine patients were not significantly reduced as compared to the data of 46 deceased epileptic control patients. A significantly decreased PB value could only be demonstrated in the temporal specimen of an old scarred infarction with complete demyelination. On the other hand a slight but significant increase of PB was observed in three neocortical samples from a child exhibiting severe brain oedema and thrombosis of the sinuses. The results favour the unspecific binding of PHT and PB to cerebral tissue constituents and do not support the hypothesis of major binding to specific receptors.

In vivo and in vitro effects of phenytoin (PHT) on ATPases and [14C]-PHT binding in synaptosomes and mitochondria from rat cerebral cortex

The effect of phenytoin (PHT) on Na(+)-K(+)-ATPase and Mg(2+)-ATPase activities and on [14C]-PHT binding in vitro to synaptosomal and mitochondrial subcellular fractions from rat cerebral cortex was studied after chronic PHT treatment. Synaptosomal and mitochondrial fractions were characterized with plasma membrane and mitochondrial enzymatic markers. Synaptosomal Na(+)-K(+)-ATPase was not affected in vitro by PHT 1-200 microM or by chronic treatment with 2-50 mg/kg/day of the unlabeled drug for 8 days. Mitochondrial Mg(2+)-ATPase was significantly stimulated by PHT after chronic treatment with 5 mg/kg/day for 8 days; reaching maximal effect (76%), at 10-25 mg/kg. PHT had no effect on mitochondrial Mg(2+)-ATPase when added in vitro. [14C]-PHT binding in vitro to the subcellular fractions was determined by dialysis to assess in vivo binding of the unlabeled PHT during chronic treatment. Indeed, [14C]-PHT bound to synaptosomes was significantly reduced by chronic PHT treatment from 218 +/- 10 to 119 +/- 11 pmol/mg protein after 1 week of treatment; a similar effect was obtained after 2-3 weeks with 10 mg/kg/day. Mitochondrial fraction bound 117 +/- 10 pmol/mg protein labeled PHT. Chronic treatment with unlabeled PHT also reduced the amount of [14C]-PHT bound to 19.9 +/- 2.2 pmol/mg protein. These results show slow reversible PHT in vivo binding to synaptosomes and mitochondrias from rat cerebral cortex, supporting the idea that the modulatory action of PHT on Na+ and Ca2+ permeabilities are mediated through these slow reversible binding proteins. The data also suggest a possible role of intrasynaptosomal mitochondria in [Ca2+]i buffering.

Phenytoin and retinal spreading depression

Several studies indicate that spreading depression is fundamentally related to seizure marches and to the aura of classical migraine. Moreover, recent investigations call attention to its possible relevance in clinical disturbances associated with brain ischemia, trauma, and hypoglycemia. The anticonvulsant phenytoin has been shown to protect the nervous tissue from the effects of anoxia and ischemia. These properties suggest that phenytoin should be able to counteract spreading depression. Therefore, we investigated its effect on spreading depression elicited by mechanical or chemical (KCl) stimulation, in isolated chick retinas. The results showed that phenytoin: (1) increases the threshold concentration of KCl to initiate the phenomenon; (2) decreases the velocity of propagation of spreading depression; (3) shortens considerably the duration of the slow potential, ionic (K+, Ca2+, Cl-), and volume changes of the extracellular compartment during spreading depression. Possible mechanisms underlying the observed effects are discussed.

Enhancement of phenytoin binding to tissues in rats by heat treatment

Phenytoin binding to heat-treated tissue homogenates has been examined to characterize the phenytoin binding to tissues. The binding to the heat-treated tissue homogenates was enhanced in all tissues studied compared with controls. The heating might produce the changes in conformation of proteins in tissues and then enhance phenytoin binding to tissue homogenates.

Potassium, pentylenetetrazol, and anticonvulsants in mouse hippocampal slices

We studied the effect of varying potassium (K+) concentrations on spontaneous and pentylenetetrazol (PTZ)-induced population burst discharges in mouse hippocampal slices. Standard techniques were used to obtain extracellular recordings in the CA3 region of hippocampal slices from Swiss-Webster mice (21-28 days old). No spontaneous burst discharges occurred at 3.25 mM K+, but population bursts were observed in 20 and 90% of the slices at 6.25 and 9.25 mM K+, respectively. In the presence of 3.25 mM K+, PTZ produced bursts in 12% of the slices at a concentration of 200 micrograms/ml, in 36% at 300 micrograms/ml, and in 40% at 400 micrograms/ml. Slices exhibiting no burst discharges in the presence of 6.25 mM K+ could be induced to do so with the addition of PTZ; bursts were produced in 11% of these slices at a PTZ concentration of 100 micrograms/ml, in 65% at 150 micrograms/ml, and in 87% at 200 micrograms/ml. The PTZ-induced bursting activity was reversible. Clonazepam abolished the bursting elicited with 200 micrograms/ml PTZ at 6.25 mM K+, and phenytoin reduced, but did not stop, bursting activity. Ethosuximide (ETH) was ineffective in stopping or reducing the burst discharges at a concentration of 125 micrograms/ml ETH was there a consistent reduction in the frequency of population bursts. The induction of PTZ discharges in the hippocampal in vitro preparation offers the advantage of a simplified model for studying the pharmacology of antiepileptic drugs.

Binding of drugs to human muscle

Binding of 22 drugs to human muscle tissue has been determined by ultrafiltration. All drugs tested were bound, the bound fraction ranging from 13% (aminophenazone) to greater than 98% (desipramine). Both linear and nonlinear binding was observed. For chemically related substances, binding to muscle tissue correlated with plasma binding and lipid solubility. There were significant differences in binding to muscle from different individuals. With respect to pharmacokinetics of drugs, it is suggested that binding to muscle tissue may be at least as important as plasma binding.

d-Amphetamine binding to brain lipid

The interaction of d-amphetamine with several brain tissue components has been investigated. A brain lipid extract and a number of individual phospholipids were found to bind d-amphetamine when measured by means of a hexane-buffer partition coefficient technique. Phosphatidylserine showed the greatest binding and phosphatidylethanolamine and dipalmitoyllecithin were also effective. Phospholipid binding of d-amphetamine was shown to be related to fatty acid composition. Cholesterol and ganglioside did not bind. It is suggested that phospholipid binding of d-amphetamine may play a role in the pharmacological action of this drug.