Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: DrugBank:APRD00512 (Phenytoin)
 1,335 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cytochrome P450IIB1,2 (nomenclature according to Nelson et al., DNA Cell Biol 12:1-51, 1993 and Volk et al., Neuroscience 42:215-235, 1991) immunoreactivity (P450-IR) is associated with astrocytes both in vivo and in vitro. Although they are unevenly distributed throughout the brain with a preference for phylogenetically elder parts, no significant differences between astrocytes prepared from different brain regions were observed in astrocyte cultures. The percentage of strongly immunoreactive astrocytes decreased from 40% after 7 days in culture to 15% after 21 days. Essentially all astrocytes have a low but significant P450-IR within this interval. Preembedding immunoelectron microscopy revealed peroxidase reaction products on the endoplasmic reticulum and on the outer membranes of mitochondrial and nuclear envelopes. Phenytoin (1 microM) added to the medium for 7 days significantly (1.22-fold) increased the amount of total P450 in astrocyte homogenates as measured by spectrophotometry. Considerably more immunoreactive cells (1.5-fold) were found in treated cultures than in controls.
 ...
PMID:Cytochrome P450 in rat astrocytes in vivo and in vitro: intracellular localization and induction by phenytoin. 789 93

The widely used anticonvulsant drug phenytoin may be bioactivated by peroxidases such as prostaglandin H synthase (PHS) to a reactive free radical intermediate that initiates teratogenesis. This in vivo study evaluated the potential molecular targets mediating phenytoin teratogenicity. In vivo phenytoin-induced oxidative tissue damage following bioactivation was quantified in both maternal hepatic and embryonic tissues from pregnant CD-1 mice using lipid peroxidation and protein oxidation and degradation as indices. Pregnant mice were injected with a teratogenic dose of phenytoin, 65 mg/kg ip, during organogenesis on Gestational Day 12. alpha-Phenyl-N-t-butylnitrone (PBN), a free radical spin trapping agent, 41.5 mg/kg, or acetylsalicylic acid (ASA), an inhibitor of the cyclooxygenase component of PHS, 10 mg/kg, were injected ip 2 hr before phenytoin treatment, and maternal hepatic and embryonic tissues were obtained at 0, 3, 6, 8, and 24 hr. Phenytoin enhanced lipid peroxidation in maternal plasma, hepatic microsomes, cytosol, mitochondria, and nuclei and in embryonic microsomes, cytosol, and mitochondria (p < 0.05). Protein oxidation was significantly increased at 3 hr after phenytoin treatment in maternal hepatic and embryonic microsomes. Phenytoin increased protein degradation in maternal plasma, RBCs, hepatic microsomes, cytosol, mitochondria, and nuclei and in embryonic microsomes, cytosol, and nuclei (p < 0.05). In embryonic microsomes, PBN maximally inhibited phenytoin-initiated lipid peroxidation at 6 hr and lipid peroxidation and protein degradation respectively at 24 hr (p < 0.05). PBN also inhibited phenytoin-initiated protein oxidation in maternal hepatic and embryonic microsomes respectively at 24 hr (p < 0.05). These data imply that a free radical generated during phenytoin bioactivation was involved in tissue damage. ASA inhibited phenytoin-induced lipid peroxidation, protein oxidation, and degradation in embryonic microsomes at 24 hr (p < 0.05), indicating that embryonic PHS may be involved in the bioactivation of phenytoin. In maternal hepatic microsomes, however, PBN and ASA did not inhibit lipid peroxidation and protein degradation, suggesting that the lipid and protein damage in maternal liver may be regulated by cytochromes P450 and/or detoxifying pathways that are lacking in embryonic tissues. Such in vivo studies cannot exclude the possibility that protein and lipid oxidation occur as the result rather than the cause of phenytoin cellular damage. However, these results, combined with previous observations, including identical results in vitro and an in vivo reduction in phenytoin teratogenicity by PBN and ASA, suggest that peroxidase-catalyzed bioactivation of phenytoin may initiate oxidative damage to lipids and proteins in embryonic tissues, with teratological consequences.
 ...
PMID:In vivo phenytoin-initiated oxidative damage to proteins and lipids in murine maternal hepatic and embryonic tissue organelles: potential molecular targets of chemical teratogenesis. 817 32

Studies on cytochrome P450 2B (CYP2B) in the brain have essentially been focused on protein characterization and regional distribution. Due to the high sequence homology between the closely related CYP2B1 and 2B2 isoforms and the low amounts of the corresponding mRNAs few efforts have been made to analyze the expression, regulation, and inducibility of these P450 genes in a specific cell type. In the present study, we investigated CYP2B mRNA expression in primary rat astrocyte cultures under the influence of the anti-epileptic drug phenytoin, which is known to be a CYP2B inducing agent in liver. In situ hybridization with a digoxigenin (DIG)-labeled cRNA probe demonstrated that 30-40% of the astrocytes strongly expressed a CYP2B mRNA-specific signal within the first week of cultivation. With increasing age (> 14 days) a greater percentage of cells (>90%) expressed mRNA for P450 2B. However, the level of transcriptional activity was substantially lower than in younger cultures. To discriminate between the 2B1 and 2B2 isoforms the reverse transcription/polymerase chain reaction (RT/PCR) procedures were proved for rat hepatic mRNA as a control assay. Subsequently, the application of this method on cultured astrocytes confirmed that these brain cells may express CYP2B1 mRNA. CYP2B2 mRNA could not be detected in astrocyte cultures at any age examined. Phenytoin led to the down regulation of CYP2B1 mRNA, which contrasts with the drug inducing effect on hepatic CYP2B1 and 2B2 levels. After 4 hr of exposure of phenytoin to the astrocytes no amplification product could be detected at all. Phenytoin did not induce either CYP2B1 or 2B2 expression.
 ...
PMID:Effect of phenytoin on cytochrome P450 2B mRNA expression in primary rat astrocyte cultures. 981 45

The anticonvulsant phenytoin (5,5-diphenylhydantoin) provokes a skin rash in 5 to 10% of patients, which heralds the start of an idiosyncratic reaction that may result from covalent modification of normal self proteins by reactive drug metabolites. Phenytoin is metabolized by cytochrome P450 (P450) enzymes primarily to 5-(p-hydroxyphenyl-),5-phenylhydantoin (HPPH), which may be further metabolized to a catechol that spontaneously oxidizes to semiquinone and quinone species that covalently modify proteins. The aim of this study was to determine which P450s catalyze HPPH metabolism to the catechol, proposed to be the final enzymatic step in phenytoin bioactivation. Recombinant human P450s were coexpressed with NADPH-cytochrome P450 reductase in Escherichia coli. Novel bicistronic expression vectors were constructed for P450 2C19 and the three major variants of P450 2C9, i.e., 2C9*1, 2C9*2, and 2C9*3. HPPH metabolism and covalent adduct formation were assessed in parallel. P450 2C19 was the most effective catalyst of HPPH oxidation to the catechol metabolite and was also associated with the highest levels of covalent adduct formation. P450 3A4, 3A5, 3A7, 2C9*1, and 2C9*2 also catalyzed bioactivation of HPPH, but to a lesser extent. Fluorographic analysis showed that the major targets of adduct formation in bacterial membranes were the catalytic P450 forms, as suggested from experiments with human liver microsomes. These results suggest that P450 2C19 and other forms from the 2C and 3A subfamilies may be targets as well as catalysts of drug-protein adduct formation from phenytoin.
 ...
PMID:Phenytoin metabolism by human cytochrome P450: involvement of P450 3A and 2C forms in secondary metabolism and drug-protein adduct formation. 1090 5

The hepatic cytochrome P450 enzyme system is involved in the metabolism of numerous drugs. Specific enzymes are associated with the metabolism of specific drugs. The potential for drug interactions arises when one drug inhibits or induces the enzyme(s) responsible for metabolism of another drug given concurrently. Most psychotropics are metabolized by these enzymes. Clinically significant drug interactions are reported between the selective serotonin reuptake inhibitors and other psychotropics. Specifically, interactions between fluoxetine and phenytoin are reported with substantial elevations of phenytoin concentrations. Phenytoin is metabolized by the CYP2C subfamily, and fluoxetine is known to inhibit this subfamily. Similarly, sertraline also inhibits the CYP2C subfamily, but no case reports to date have been identified. To minimize and prevent these interactions, one must be aware of the P450 enzymes involved in drug metabolism. The significance of these interactions seems to rely both on the concentration of the drug at the enzyme and its potency for inhibiting the enzyme. Frequent monitoring of serum concentrations of drugs with a narrow therapeutic range would be appropriate when a potential inhibitor is added. This article describes an apparently similar interaction between sertraline and phenytoin in two elderly patients, which resulted in elevated phenytoin concentrations without symptoms of toxicity.
 ...
PMID:Elevated serum phenytoin concentrations associated with coadministration of sertraline. 1095 Apr 73

[4-(14)C]Phenytoin underwent a rapid cellular uptake by diffusion within 5 min when applied in a concentration of 10 microM to mouse brain astrocyte cultures. Subsequently, a slow linear increase of intracellular radioactivity indicated metabolic trapping of the drug, with final concentrations reaching 144 pmol phenytoin/mg protein in the astrocytes. Phenytoin levels from 1 to 10 microM decreased cell viability by 15%. The action of cytochrome P450 present in astrocytes in concentrations of 16-17 pmol P450/mg protein could explain these slight cytotoxic effects by generating intermediate metabolites of phenytoin. In contrast, concentrations of 50 microM strongly inhibited cell proliferation. A Cyp2c29 immunorelated P450 isoform was expressed in nearly all astrocytes in culture. Intracellular [4-(14)C]phenytoin was degraded to its major metabolites dihydrodiol, p-HPPH, and m-HPPH through a P450-dependent reaction with a specific activity of 0.66 pmol/min x mg protein, or 0.12 pmol/min x mg protein as measured in cell homogenates. These data underscore the importance of astrocytes as brain cells active in the detoxification of foreign substrates, but also in their toxification due to reactive metabolites generated during these metabolic processes. After diffusionary influx of drugs and other xenobiotics, the astrocyte P450 monooxygenases perform an essential role in the mediation of toxicity most frequently encountered in highly vulnerable neurons.
 ...
PMID:Possible function of astrocyte cytochrome P450 in control of xenobiotic phenytoin in the brain: in vitro studies on murine astrocyte primary cultures. 1116 26

Phenytoin, 5,5-diphenylhydantoin, is a widely used anticonvulsant agent with a variety of toxicities, including drug interactions. The formation of four oxidative metabolites, 4'-hydroxylated (4'-HPPH), 3'-hydroxylated (3'-HPPH), a catechol (3',4'-diHPPH), and the 3',4'-dihydrodiol form of phenytoin was examined in rat liver microsomes. In 11 cDNA-expressed rat P450 enzymes tested, CYP2C6 had the highest activities in 4'- and 3'-HPPH formation from phenytoin, followed only by CYP2C11. In contrast, CYP2C11 had high activity for 3',4'-diHPPH formation from 4'-HPPH, followed by CYP2C6. The rates of 4'-HPPH and 3',4'-diHPPH formation from phenytoin in liver microsomes in the presence of NADPH were significantly decreased by oral administration of phenytoin (300 mg/kg for 20 days) to rats, despite the increase in P450 contents. However, the cumene hydroperoxide-supported formation of 3',4'-dihydrodiol and 4'-HPPH from phenytoin was induced by phenytoin administration. Hydrogen peroxide formation in reaction mixtures with NADPH was induced by the administration of phenytoin; however, the coupling ratio of phenytoin oxidation was decreased in phenytoin-induced liver microsomal P450 systems. These results suggested that phenytoin could not stimulate its own apparent oxidative metabolism by liver P450s induced with phenytoin administration. The increase of unmetabolized phenytoin and byproducts of oxygen generated in the phenytoin-induced liver microsomal P450 system may be involved in phenytoin-related drug toxicity.
 ...
PMID:Decreases in phenytoin hydroxylation activities catalyzed by liver microsomal cytochrome P450 enzymes in phenytoin-treated rats. 1125 27

The human CYP2Cs are an important subfamily of P450 enzymes that metabolize approximately 20% of clinically used drugs. There are four members of the subfamily, CYP2C8, CYP2C9, CYP2C19, and CYP2C18. Of these CYP2C8, CYP2C9, and CYP2C19 are of clinical importance. The CYP2Cs also metabolize some endogenous compounds such as arachidonic acid. Each member of this subfamily has been found to be genetically polymorphic. The most well-known of these polymorphisms is in CYP2C19. Poor metabolizers (PMs) of CYP2C19 represent approximately 3-5% of Caucasians, a similar percentage of African-Americans and 12-100% of Asian groups. The polymorphism affects metabolism of the anticonvulsant agent mephenytoin, proton pump inhibitors such as omeprazole, the anxiolytic agent diazepam, certain antidepressants, and the antimalarial drug proguanil. Toxic effects can occur in PMs exposed to diazepam, and the efficacy of some proton pump inhibitors may be greater in PMs than EMs at low doses of these drugs. A number of mutant alleles exist that can be detected by genetic testing. CYP2C9 metabolizes a wide variety of drugs including the anticoagulant warfarin, antidiabetic agents such as tolbutamide, anticonvulsants such as phenytoin, and nonsteroidal anti-inflammatory drugs. The incidence of functional polymorphisms is much lower, estimated to be 1/250 in Caucasians and lower in Asians. However, the clinical consequences of these rarer polymorphisms can be severe. Severe and life-threatening bleeding episodes have been reported in CYP2C9 PMs exposed to warfarin. Phenytoin has been reported to cause severe toxicity in PMs. New polymorphisms have been discovered in CYP2C8, which metabolizes taxol (paclitaxel). Genetic testing is available for all of the known CYP2C variant alleles.
 ...
PMID:Clinical relevance of genetic polymorphisms in the human CYP2C subfamily. 1196 80

Inactivation of testosterone by specific hydroxylations is a main function of cytochrome P450 (P450, CYP) in the brain. Recent data imply that induction of brain P450s by neuroactive drugs alters steroid hormone levels and endocrine signalling, giving rise to endocrine disorders. In this study, we investigated this drug-hormone crosstalk in mouse brain. Phenytoin led to a significant increase of 2alpha-, 2beta-, 6beta-, 16alpha- and 16beta-hydroxytestosterones, while 6alpha- and 15alpha-hydroxytestosterones showed no significant alteration of their metabolism compared with untreated controls. Inhibition of testosterone hydroxylation using the chemical inhibitors orphenadrine, chloramphenicol, ketoconazole and nifedipine as well as antibodies against CYP3A- and 2B-isoforms pointed to major role of Cyp3a11 and an only minor function of Cyp2b9/10 in mouse brain. Cyp3a11 revealed to be the major isoform affected by phenytoin. There was considerable overlap of Cyp3a11 and AR expression in neuronal structures of the limbic system, namely the hippocampus, amygdala, hypothalamus and thalamus. Phenytoin treatment led to an increase of both, Cyp3a11 and AR expression in the limbic system. Additionally, the coherence between CYP3A and AR expression was analysed in PC-12 cells. Inhibition of phenytoin-induced endogenous CYP3A2 and AR by ketoconazole led a reduction of their expression to basal levels. We conclude that Cyp3a11 plays a crucial role in directing drug action to hormonal response within the limbic system of mouse brain in a so-called drug-hormone crosstalk.
 ...
PMID:Concordant up-regulation of cytochrome P450 Cyp3a11, testosterone oxidation and androgen receptor expression in mouse brain after xenobiotic treatment. 1922 68

Phenytoin, 5,5-diphenylhydantoin (DPH), is widely used as an anticonvulsant agent. Severe hepatic injury rarely occurs in patients who received DPH. The development of liver injury is thought to be caused by reactive metabolites; however, the metabolites suggested to contribute to hepatotoxicity have not yet been detected in vivo and their effect on developing the liver injury is largely unknown. We recently demonstrated that DPH treatment decreased hepatic glutathione (GSH) contents, and GSH-depleted condition exacerbated DPH-induced liver injury in mice. The aim of the present study was to identify the reactive metabolite and to investigate the role of P450-mediated metabolisms in DPH-induced liver injury. We identified a novel GSH-conjugated (GS)-DPH, a conjugate of putative electrophilic arene oxide intermediate with GSH, in the bile of mice with DPH-induced liver injury. In plasma, cysteine- or N-acetylcysteine-conjugated DPH was detected, and these thiol conjugates levels were correlated with the plasma alanine aminotransferase (ALT) levels. These changes were significantly reduced by pretreatment with P450 inhibitor. Furthermore, the increases of hepatic P450 activities were in parallel with elevation of plasma thiol conjugates levels. These findings suggest that the arene oxide intermediate, which can be converted to thiol conjugates, is involved in DPH-induced liver injury.
...
PMID:Role of cytochrome P450-mediated metabolism and identification of novel thiol-conjugated metabolites in mice with phenytoin-induced liver injury. 2545 49


1