Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Phenytoin, at 50 to 200 micrograms reduced the maximum upstroke velocity of action potentials (Vmax) with increases in frequency from 0.25 to 5 Hz and in the external potassium concentration [( K+]0) from 2.7 to 8.1 mM. The drug-induced shortening of action potential duration was evident at 0.25 to 2 Hz but little at 3 to 5 Hz. Time courses of recovery of Vmax was studied by applying premature responses between the conditioning responses at 1 Hz both in control and in drug-treated preparations. Concerning the time courses of the difference between the Vmax values before and after drug treatments at the same diastolic interval, with increases in drug concentrations the intercepts at APD90 were increased but the time constants were not changed or slightly decreased in 8.1 to 5.4 mM [K+]0, whereas they were increased in 2.7 mM [K+]0. To understand the kinetic behavior of this drug on sodium channels, rate constants for the interaction of phenytoin with three states of channels in terms of Hondeghem-Katzung model were estimated from the above experiments of Vmax. The model most consistent with the present experiments was that with an affinity for inactivated channels 20 times greater than that for resting channels and with a minor affinity for open channels. Phenytoin produced a delay in the time course of recovery of overshoot and action potential duration at 0 mV (APD0), suggesting an additional inhibition of the slow channel by this drug.
J Mol Cell Cardiol 1986 Jul
PMID:Frequency-dependent effects of phenytoin on the maximum upstroke velocity of action potentials in guinea-pig papillary muscles. 242 31

We evaluated the role of microtubule assembly in phenytoin (5-5-diphenylhydantoin) teratogenic activity in the sea urchin embryo. Zygotes were exposed to phenytoin or one of several phenytoin analogs within 15 min of fertilization and the frequency of the resultant malformations was assessed at the cleavage and late gastrula (prism) stages. Concomitant studies of drug uptake into zygotes and drug effects on both microtubule assembly in vitro and spindle morphology in situ were also performed. Phenytoin, 5-p-methylphenyl-5-phenylhydantoin, and 5-p-methoxyphenyl-5-phenylhydantoin were teratogenic (approaching 100% affected embryos) at both developmental stages were concentrated rapidly by the zygotes, and induced a shortened mitotic spindle in situ. In a separate in vitro system using porcine brain microtubular protein, these analogs were shown to inhibit microtubule assembly directly. The major human metabolite of phenytoin, 5-p-hydroxyphenyl-5-phenylhydantoin was teratogenic at the prism stage but induced only a 20% incidence of abnormal embryos at the first cleavage. This was attributed to the slow rate of uptake of this analog. This compound inhibited microtubule assembly in the in vitro assay and also shortened the mitotic spindle to an extent proportional to its observed weak effect on the first cleavage. Another analog, 5-p-hydroxyphenyl-5-p'-methylphenylhydantoin was not teratogenic at concentrations up to the limit of its solubility (285 microM). If this analog were as potent inside the cell as either phenyltoin or 5-p-hydroxyphenyl-5-phenylhydantoin, the intracellular concentrations achieved should have been sufficient to induce abnormal cleavage. Thus, the lack of teratogenic efficacy of this analog was correlated with its observed lack of effects on either microtubule assembly in vitro or spindle formation in situ. The anticonvulsant drug ethotoin was not teratogenic at concentrations up to 2.93 mM, apparently due to either poor uptake or inability to inhibit microtubule assembly or both. Overall, these studies are consistent with a hypothesis that phenytoin may induce abnormal development in this system by a direct inhibition of microtubule assembly.
Mol Pharmacol 1989 Nov
PMID:Role of microtubule assembly in phenytoin teratogenic action in the sea urchin (Arbacia punctulata) embryo. 258 88

The mode of action of the antiarrhythmic drug, phenytoin, on the cardiac sodium current was investigated using isolated rat ventricular cells, under voltage clamp conditions. It was found that the blocking effect of phenytoin on INa displays both voltage- and use-dependence. At a concentration of 20 mumol/l, it produced a tonic block of INa measuring 18% of control. After a train of 10 depolarizing pulses of 500 ms duration (applied at a frequency of 1 Hz), the degree of block was increased to 45% of control. Phenytoin also shifted the steady-state inactivation curve of INa to more hyperpolarized potentials by 5.4 mV. The blocking effects of phenytoin during repetitive depolarizing voltage steps suggest that phenytoin binds preferentially to inactivated channels, and that removal of this block may primarily occur from resting channels; moreover, the removal of block is strongly voltage-dependent.
J Mol Cell Cardiol 1983 Aug
PMID:Effect of phenytoin on the sodium current in isolated rat ventricular cells. 632 24

A murine embryo culture model was used to investigate phenytoin-initiated embryonic DNA oxidation and dysmorphogenesis and to determine the embryoprotective potential of superoxide dismutase and catalase, which detoxify reactive oxygen species. Gestational day 9.5 CD-1 embryos were cultured for up to 24 hr at 37 degrees in medium containing phenytoin (20 micrograms/ml, 80 microM) or its vehicle (0.002 N NaOH). Embryos cultured for 24 hr were examined for embryotoxicity. After varying durations of incubation, embryonic DNA was isolated and purified, and DNA oxidation was determined from the formation of 8-hydroxy-2'-deoxyguanosine (8-OH-2'-dG). Control embryos showed an early increase in 8-OH-2'-dG levels that was maximal between 2 and 4 hr, followed by a small but significant decrease over 24 hr, with no evidence of embryopathy. Phenytoin-treated embryos within 4 hr also demonstrated maximal 8-OH-2'-dG formation, which was substantially greater than that of controls, with a maximal 3-fold increase over controls at 24 hr (p < 0.05). In wash-out studies, embryos removed from the phenytoin-containing medium after 4 hr and then cultured in phenytoin-free medium for an additional 20-hr period showed no decrease in either 8-OH-2'-dG levels or embryotoxicity, compared with embryos incubated in the presence of phenytoin for 24 hr. Embryos exposed to phenytoin demonstrated substantial dysmorphogenesis, as evidenced by decreases in anterior neuropore closure, turning, yolk sac diameter, crown-rump length, and somite development (p < 0.05). Superoxide dismutase and catalase virtually eliminated phenytoin-initiated 8-OH-2'-dG formation and reduced or completely eliminated all phenytoin-initiated dysmorphological anomalies (p < 0.05). These results suggest that embryonic DNA oxidation constitutes teratologically important molecular target damage, and they provide the first direct evidence that free radical-mediated oxidative stress plays a critical role in phenytoin teratogenesis.
Mol Pharmacol 1995 Jul
PMID:Phenytoin-initiated DNA oxidation in murine embryo culture, and embryo protection by the antioxidative enzymes superoxide dismutase and catalase: evidence for reactive oxygen species-mediated DNA oxidation in the molecular mechanism of phenytoin teratogenicity. 762 65

A mouse embryo culture model was used to determine whether embryonic prostaglandin H synthase (PHS)-catalyzed bioactivation and resultant oxidative damage to embryonic protein and DNA may constitute a molecular mechanism mediating phenytoin and benzo[a]pyrene teratogenesis. Embryos were explanted from CD-1 mouse dams on gestational day 9.5 (vaginal plug = day 1) and incubated for either 4 h (biochemistry) or 24 h (embryotoxicity) at 37 degrees C in medium containing either phenytoin (20 micrograms/ml, 80 microM), benzo[a]pyrene (10 microM), or their respective vehicles. As previously observed with phenytoin (Mol. Pharmacol.48: 112-120, 1995), embryos incubated with benzo[a]pyrene showed decreases in anterior neuropore closure, turning, yolk sac diameter, and somite development (p < .05). Addition of the antioxidative enzyme superoxide dismutase (SOD) substantially enhanced embryonic SOD activity (p < .05) and completely inhibited benzo[a]pyrene embryotoxicity (p < .05). Substantial PHS was detected in day 9.5 embryos using SDS/PAGE, anti-PHS antibody, and alkaline phosphatase-conjugated donkey anti-goat IgG. Embryonic protein oxidation was detected by the reaction of 0.5 mM 2,4-dinitrophenylhydrazine with protein carbonyl groups. This method was first validated by using a known hydroxyl radical-generating system consisting of vanadyl sulfate and H2O2, with bovine serum albumin or embryonic protein as the target. Embryonic proteins were characterized by SDS/PAGE, anti-dinitrophenyl antisera, and peroxidase-labeled goat anti-donkey IgG. Using enhanced chemiluminescence, the number and content of oxidized protein bands detected between 25 and 200 kDa were substantially increased by both phenytoin and benzo[a]pyrene. Addition of the reducing agent dithiothreitol, or SOD or catalase, decreased protein oxidation in phenytoin-exposed embryos. Both phenytoin (Mol. Pharmacol.48: 112-120, 1995) and benzo[a]pyrene enhanced embryonic DNA oxidation, determined by the formation of 8-hydroxy-2'-deoxyguanosine, as measured by high-performance liquid chromatography (HPLC) (p < .05). Phenytoin also enhanced the oxidation of embryonic glutathione (GSH) to its GSSG disulfide, as measured by HPLC (p < .05). These results provide direct evidence that, in the absence of maternal or placental processes, embryonic PHS-catalyzed bioactivation and reactive oxygen species-mediated oxidation of embryonic protein, thiols, and DNA may constitute a molecular mechanism mediating phenytoin and benzo[a]pyrene teratogenesis.
 ...
PMID:Evidence for embryonic prostaglandin H synthase-catalyzed bioactivation and reactive oxygen species-mediated oxidation of cellular macromolecules in phenytoin and benzo[a]pyrene teratogenesis. 901 24

The effects of anticonvulsants on the activities of cytochromes P-450(17alpha,lyase) (CYP17), P-450arom (CYP19), P-450C21 (CYP21), P-450SCC (CYP11A1), and P-450(11beta) (CYP11B1) mono-oxygenase systems were studied using rat testicular microsomes, human placental microsomes, bovine adrenocortical microsomes, bovine adrenocortical mitochondria and purified cytochrome P-450(11beta). Phenytoin, clonazepam and carbamazepine inhibited the steroidogenesis catalysed by these cytochrome P-450 mono-oxygenase systems and the Ki values for each anticonvulsant were determined. Neither hydantoin nor sodium valproate inhibited the activities of steroidogenic cytochromes P-450. When the activities of cytochromes P-450arom and P-450C21 were measured in the presence of anticonvulsants, the Ki values (0.15 mM) for phenytoin were close to the plasma concentration of phenytoin under therapeutic conditions. Phenytoin, clonazepam and carbamazepine directly inhibited the monooxygenase activities of cytochromes P-450, because they did not affect the activities of NADPH-cytochrome P-450 reductase, NADPH-adrenoferredoxin reductase and adrenoferredoxin.
J Steroid Biochem Mol Biol 1997 Jan
PMID:Direct inhibitions of the activities of steroidogenic cytochrome P-450 mono-oxygenase systems by anticonvulsants. 918 61

Phenytoin, carbamazepine, and lamotrigine are anticonvulsants frequently prescribed in seizure clinics. These drugs all show voltage-dependent inhibition of Na+ currents, which has been implicated as the major mechanism underlying the antiepileptic effect. In this study, I examine the inhibition of Na+ currents by mixtures of different anticonvulsants. Quantitative analysis of the shift of steady state inactivation curve in the presence of multiple drugs argues that one channel can be occupied by only one drug molecule. Moreover, the recovery from inhibition by a mixture of two drugs (a fast-unbinding drug plus a slow-unbinding drug) is faster, or at least not slower, than the recovery from inhibition by the slow-unbinding drug alone. Such kinetic characteristics further strengthen the argument that binding of one anticonvulsant to the Na+ channel precludes binding of the other. It also is found that these anticonvulsants are effective inhibitors of Na+ currents only when applied externally, not internally. Altogether these findings suggest that phenytoin, carbamazepine, and lamotrigine bind to a common receptor located on the extracellular side of the Na+ channel. Because these anticonvulsants all have much higher affinity to the inactivated state than to the resting state of the Na+ channel, the anticonvulsant receptor probably does not exist in the resting state. Thus, there may be correlative conformational changes for the making of the receptor on the extracellular side of the channel during the gating process.
Mol Pharmacol 1998 Oct
PMID:A common anticonvulsant binding site for phenytoin, carbamazepine, and lamotrigine in neuronal Na+ channels. 976 15

It is estimated that about 2.5 million people only in the United States are affected by epilepsy. Labelled red blood cells (RBC) and plasma proteins (PP) are used for several evaluations in nuclear medicine and drugs affecting those labelings have previously been described. The aim of this study was to evaluate whether the most popular antiseizure drugs interfere with the 99mTc labeling process of RBC and PP. Heparinized blood withdrawn from Wistar rats was incubated with phenobarbital (0.2, 2, 20, 200, 2,000 microg/ml), phenytoin (0.15, 1.5, 15, 150, 1,500 microg/ml), carbamazepine (0.7, 7, 70 microg/ml), clonazepam (0.5, 5, 50, 500 microg/ml) or valproic acid (0.5, 5, 50, 500 microg/ml) for I hr. Stannous chloride (SnCl2), in two different concentrations (0.012 or 1.2 microg/ml) and 99mTc were added. Plasma and cellular fractions were isolated by centrifugation, soluble and insoluble fractions were separated by trichloroacetic acid precipitation. The percentage of radioactivity was calculated for each fraction. Statistical analysis was performed with ANOVA and Dunnet tests. The analysis of the results has shown that phenobarbital (2,000 microg/ml) and clonazepam (50 microg/ml) significantly have reduced the RBC labeling efficiency when it was used the optimal SnCl2 concentration (1.2 microg/ml) and clonazepam (5, 50 microg/ml) has significantly decreased the PP labeling efficiency with 99mTc. Phenytoin (1,500 microg/ml) has decreased the RBC labeling efficiency when the experiments were carried out with a small SnCl2 concentration (0.012 microg/ml). We can suggest that with this in vitro assay, at the therapeutic level of phenytoin, phenobarbital, carbamazepine and valproic acid will not interfere on the 99mTc labeling process of RBC. Interference is displayed at higher phenobarbital concentrations (2,000 microg/ml). However, humans do not tolerate this concentration. On the other hand, a decreased RBC and PP labeling efficiency with 99mTc may be expected for clonazepam at therapeutic levels.
Cell Mol Biol (Noisy-le-grand) 2002 Nov
PMID:Assessment of the effect of antiseizure drugs on the labeling process of red blood cells and plasma proteins with technetium-99m. 1261 78

Endogenous and xenobiotic-enhanced oxidative stress may initiate embryonic death and birth defects via reactive oxygen species (ROS) signaling pathways involving nuclear transcription factor-kappaB (NF-kappaB). Using embryo culture and a transgenic mouse engineered with a NF-kappaB-dependent beta-galactosidase reporter gene, we employed NF-kappaB antisense oligonucleotide therapy to determine whether NF-kappaB signaling contributes to the embryopathic effects of the ROS-initiating teratogen phenytoin. Phenytoin selectively increased NF-kappaB activity in target tissues and caused embryopathies, both of which were blocked by NF-kappaB antisense oligonucleotides but not by sense and nonsense oligonucleotide controls. NF-kappaB signaling may therefore contribute to the mechanism of ROS-mediated embryopathies.
Mol Pharmacol 2004 Sep
PMID:Antisense evidence for nuclear factor-kappaB-dependent embryopathies initiated by phenytoin-enhanced oxidative stress. 1532 31

Previous studies have shown a role for multiple drug resistance proteins in protecting the fetus from a limited number of teratogens. We have expanded the number of proteins and teratogens examined by comparing the influence of the mdr1a and mdr2 proteins on teratogen-induced orofacial clefting using their respective knockouts in crosses with the A/J, high susceptibility strain. Western blots identified the presence of mdr1a and possibly mdr2 in the placenta and fetus. The mdr1a knockout, on its unique genetic background showed lower, similar, and higher incidences of clefting compared to A/J for Dilantin, hydrocortisone (HC), and 6-aminonicotinamide (6-AN), respectively. The mdr2 knockout did not affect 6-AN clefting when compared to A/J. In reciprocal crosses, when corrected for increased spontaneous clefting, maternally inherited A/J susceptibility genes predominated over the effects of the maternal absence of mdr1a (with 6-AN). Unlike mdr1a, which had a direct effect in the fetus as shown by genotyping of affected versus unaffected fetuses, an effect of mdr2 in the fetus was not found. The mdr1a knockout was backcrossed to the A/J inbred strain for 11 generations (congenics) to eliminate genetic background effects. Reciprocal crosses showed no maternal effect from the lack of mdr1a, confirming that mdr1a expression in the fetus, rather than the placenta, protects the fetus from teratogens. Mdr2 seems not to be involved in the protection of the fetus from teratogens.
Mol Reprod Dev 2007 Nov
PMID:The role of multiple drug resistance proteins in fetal and/or placental protection against teratogen-induced orofacial clefting. 1744 Sep 29


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