Expression of multiple forms of brain cytochrome P450

Immunochemical and Biochemical Evidence for Expression of Phenobarbital-and 3-Methylcholanthrene-Inducible Isoenzymes of Cytochrome P450 in Rat Brain

Expression of P450 1A1l 1A2 and 2 B1l 2B2 isoenzymes in rat brain was studied by Western blotting, using polyclonal antibodies raised against hepatic P450 1A1l 1A2 and 2B1l 2B2 isoenzymes. In addition, biochemical characterizations of the catalytic activities, pen toxyresorufin O-dealkylation (PROD) and ethoxyre-sorufin O-deethylation (EROD), selective for P450 2B1l 2B2 (PROD) and P450 1A1l 1A2 (EROD), were performed with rat brain microsomes. Control rat brain microsomes did not crossreact with either of the antibodies, whereas microsomes obtained from 3-methylcholanthrene (MC)-pretreated rats revealed significant immunoreactivity with anti-P450 1A1l 1A2. Similar results were observed with phenobarbital (PB)-pretreated rats, with the brain microsomes exhibiting significant immunoreactivity with anti-P450 2B1l 2B2. The induction in the P450 isoenzymes after PB or MC pretreatment was much less in the brain in comparison to the liver. Enzymatic studies indicated that the activities of PROD and EROD were induced in brain 3—4 fold by PB and MC pretreatment, respectively, and were almost completely inhibited on in vitro addition of anti-P450 2B1l 2B2 and 1A1l 1A2. These data demonstrate the expression of P4501A1l 1A2 and 2B1l 2B2 isoenzymes in the brain and indicate that, as in liver, these isoenzymes catalyze EROD and PROD, respectively, in the rat brain.

Assessment of neurotoxicity of monocrotaline, an alkaloid extracted from Crotalaria retusa in astrocyte/neuron co-culture system

Studies have shown cases of poisoning with plants from the genus Crotalaria (Leguminosae) mainly in animals. They induce damages in the central nervous system (CNS), which has been attributed to toxic effects of the pyrrolizidine alkaloid (PA) monocrotaline (MCT). Previously we demonstrated that both MCT and dehydromonocrotaline (DHMC), its main active metabolite, induce changes in the levels and patterns of expression of the main protein from astrocyte cytoskeleton, glial fibrillary acidic protein (GFAP). In this study we investigated the effect of MCT on rat cortical astrocyte/neuron primary co-cultures. Primary cultures were exposed to 10 or 100 μM MCT. The MTT test and the measurement of LDH activity on the culture medium revealed that after 24h exposure MCT was not cytotoxic to neuron/astrocyte cells. However, the cell viability after 72 h treatment decreased in 10-20%, and the LDH levels in the culture medium increased at a rate of 12% and 23%, in cultures exposed to 10 or 100 μM MCT. Rosenfeld staining showed vacuolization and increase in cell body in astrocytes after MCT exposure. Immunocytochemistry and Western blot analyses revealed changes on pattern of GFAP and βIII-tubulin expression and steady state levels after MCT treatment, with a dose and time dependent intense down regulation and depolarization of neuronal βIII-tubulin. Moreover, treatment with 100 μM MCT for 12h induced GSH depletion, which was not seen when cytochrome P450 enzyme system was inhibited indicating that it is involved in MCT induced cytotoxicity in CNS cells.

Cytochrome P450 2D6 enzyme neuroprotects against 1-methyl-4-phenylpyridinium toxicity in SH-SY5Y neuronal cells

Cytochrome P450 (CYP) 2D6 is an enzyme that is expressed in liver and brain. It can inactivate neurotoxins such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, 1,2,3,4-tetrahydroisoquinoline and beta-carbolines. Genetically slow CYP2D6 metabolizers are at higher risk for developing Parkinson's disease, a risk that increases with exposure to pesticides. The goal of this study was to investigate the neuroprotective role of CYP2D6 in an in-vitro neurotoxicity model. SH-SY5Y human neuroblastoma cells express CYP2D6 as determined by western blotting, immunocytochemistry and enzymatic activity. CYP2D6 metabolized 3-[2-(N,N-diethyl-N-methylammonium)ethyl]-7-methoxy-4-methylcoumarin and the CYP2D6-specific inhibitor quinidine (1 microM) blocked 96 +/- 1% of this metabolism, indicating that CYP2D6 is functional in this cell line. Treatment of cells with CYP2D6 inhibitors (quinidine, propanolol, metoprolol or timolol) at varying concentrations significantly increased the neurotoxicity caused by 1-methyl-4-phenylpyridinium (MPP+) at 10 and 25 microM by between 9 +/- 1 and 22 +/- 5% (P < 0.01). We found that CYP3A is also expressed in SH-SY5Y cells and inhibiting CYP3A with ketoconazole significantly increased the cell death caused by 10 and 25 microM of MPP+ by between 8 +/- 1 and 30 +/- 3% (P < 0.001). Inhibiting both CYP2D6 and CYP3A showed an additive effect on MPP+ neurotoxicity. These data further support a possible role for CYP2D6 in neuroprotection from Parkinson's disease-causing neurotoxins, especially in the human brain where expression of CYP2D6 is high in some regions (e.g. substantia nigra).

Overexpression of cytochrome P450 NADPH reductase sensitises MDA 231 breast carcinoma cells to 5-fluorouracil: possible mechanisms involved

Activity of cytochromes P450 is highly dependent on cytochrome P450 NADPH reductase (P450R), but this enzyme can also metabolise drugs on its own. MDA 231 breast adenocarcinoma cells transfected with human P450R (MDA R4) or an empty vector (MDA EV) were exposed to a series of commonly used chemotherapeutic drugs. Overexpression of P450R did not affect cell sensitivity to cisplatin, mitoxantrone, paclitaxel, docetaxel, vincristine or etoposide. However, MDA R4 cells showed increased sensitivity to mitomycin C (6.6-fold) and also to 5-fluorouracil (2.8-fold). In vitro toxicity assays where mitomycin C, 5-fluorouracil and vincristine were preincubated with microsomes expressing recombinant P450R showed that this effect was not a result of direct metabolism by P450R. Levels of NADPH were considerably decreased in MDA R4 as compared to MDA EV cells, while reactive oxygen species (ROS) production was increased in MDA R4 cells in basal conditions, showing no significant further increase after treatment with mitomycin C or 5-fluorouracil. P450R overexpression appears therefore to be detrimental to MDA 231 cells, depleting NADPH and increasing ROS levels; the increased oxidative stress observed in MDA R4 cells might explain the enhanced sensitivity to 5-fluorouracil. Expression of this enzyme in tumour cells might therefore modulate response to 5-fluorouracil.

Recurrent headache as the main symptom of acquired cerebral toxoplasmosis in nonhuman immunodeficiency virus-infected subjects with no lymphadenopathy: the parasite may be responsible for the neurogenic inflammation postulated as a cause of different types of headaches

Headache and/or migraine, a common problem in pediatrics and internal medicine, affect about 5% to 10% children and adolescents, and nearly 30% of middle-aged women. Headache is also one of the most common clinical manifestations of acquired Toxoplasma gondii infection of the central nervous system (CNS) in immunosuppressed subjects. We present 11 apparently nonhuman immunodeficiency virus-infected children aged 7 to 17 years (8 girls, 3 boys) and 1 adult woman with recurrent severe headaches in whom latent chronic CNS T. gondii infection not manifested by enlarged peripheral lymph nodes typical for toxoplasmosis, was found. In 7 patients, the mean serum IgG Toxoplasma antibodies concentration was 189 +/- 85 (SD) IU/mL (range 89 to 300 IU/mL), and in 5 other subjects, the indirect fluorescent antibody test titer ranged from 1:40 to 1:5120 IU/mL (n= <1:10 IU/mL). Some of the patients suffered also from atopic dermatitis (AD) and were exposed to cat and/or other pet allergens, associated with an increased IL-4 and decreased IFN-gamma production. These cytokine irregularities caused limited control of cerebral toxoplasmosis probably because IL-4 down-regulated both the production of IFN-gamma and its activity, and stimulated production of a low NO-producing population of monocytes, which allowed cysts rupture, increased parasite multiplication and finally reactivation of T. gondii infection. The immune studies performed in 4 subjects showed a decreased percentage of T lymphocytes, increased total number of lymphocytes B and serum IgM concentration, and impaired phagocytosis. In addition, few of them had also urinary tract diseases known to produce IL-6 that can mediate immunosuppressive functions, involving induction of the anti-inflammatory cytokine IL-10. These disturbances probably resulted from the host protective immune reactions associated with the chronic latent CNS T. gondii infection/inflammation. This is consistent with significantly lower enzyme indoleamine 2,3-dioxygenase (IDO) activity reported in atopic than in nonatopic individuals, and an important role that IDO and tryptophan degradation pathways plays in both, the host resistance to T. gondii infection and its reactivation. Analysis of literature information on the subjects with different types of headaches caused by foods, medications, and other substances, may suggest that their clinical symptoms and changes in laboratory data result at least in part from interference of these factors with dietary tryptophan biotransformation pathways. Several of these agents caused headache attacks through enhancing NO production via the conversion of arginine to citrulline and NO by the inducible nitric oxide synthase enzyme, which results in the high-output pathway of NO synthesis. This increased production of NO is, however, quickly down-regulated by NO itself because this biomolecule can directly inactivate NOS, may inhibit Ia expression on IFN-gamma-activated macrophages, which would limit antigen-presenting capability, and block T-cell proliferation, thus decreasing the antitoxoplasmatic activity. Moreover, NO inhibits IDO activity, thereby suppressing kynurenine formation, and at least one member of the kynurenine pathway, 3-hydroxyanthranilic acid, has been shown to inhibit NOS enzyme activity, the expression of NOS mRNA, and activation of the inflammatory transcription factor, nuclear factor-kB. In addition, the anti-inflammatory cytokines IL-4 and IL-10, TGF-beta, and a cytokine known as macrophage deactivating factor, have been shown to directly modulate NO production, sometimes expressing synergistic activity. On the other hand, IL-4 and TGF-beta can suppress IDO activity in some cells, for example human monocytes and fibroblasts, which is consistent with metabolic pathways controlled by IDO being a significant contributor to the proinflammatory system. Also, it seems that idiopathic intracranial hypertension, pseudotumor cerebri, and aseptic meningitis, induced by various factors, may result from their interference with IDO and inducible nitric oxide synthase activities, endogenous NO level, and cytokine irregularities which finally affect former T. gondii status 2mo in the brain. All these biochemical disturbances caused by the CNS T. gondii infection/inflammation may also be responsible for the relationship found between neurologic symptoms, such as headache, vertigo, and syncope observed in apparently immunocompetent children and adolescents, and physical and psychiatric symptoms in adulthood. We therefore believe that tests for T. gondii should be performed obligatorily in apparently immunocompetent patients with different types of headaches, even if they have no enlarged peripheral lymph nodes. This may help to avoid overlooking this treatable cause of the CNS disease, markedly reduce costs of hospitalization, diagnosis and treatment, and eventually prevent developing serious neurologic and psychiatric disorders.

Rescue of cytochrome P450 oxidoreductase (Por) mouse mutants reveals functions in vasculogenesis, brain and limb patterning linked to retinoic acid homeostasis

Cytochrome P450 oxidoreductase (POR) acts as an electron donor for all cytochrome P450 enzymes. Knockout mouse Por(-/-) mutants, which are early embryonic (E9.5) lethal, have been found to have overall elevated retinoic acid (RA) levels, leading to the idea that POR early developmental function is mainly linked to the activity of the CYP26 RA-metabolizing enzymes (Otto et al., Mol. Cell. Biol. 23, 6103-6116). By crossing Por mutants with a RA-reporter lacZ transgene, we show that Por(-/-) embryos exhibit both elevated and ectopic RA signaling activity e.g. in cephalic and caudal tissues. Two strategies were used to functionally demonstrate that decreasing retinoid levels can reverse Por(-/-) phenotypic defects, (i) by culturing Por(-/-) embryos in defined serum-free medium, and (ii) by generating compound mutants defective in RA synthesis due to haploinsufficiency of the retinaldehyde dehydrogenase 2 (Raldh2) gene. Both approaches clearly improved the Por(-/-) early phenotype, the latter allowing mutants to be recovered up until E13.5. Abnormal brain patterning, with posteriorization of hindbrain cell fates and defective mid- and forebrain development and vascular defects were rescued in E9.5 Por(-/-) embryos. E13.5 Por(-/-); Raldh2(+/-) embryos exhibited abdominal/caudal and limb defects that strikingly phenocopy those of Cyp26a1(-/-) and Cyp26b1(-/-) mutants, respectively. Por(-/-); Raldh2(+/-) limb buds were truncated and proximalized and the anterior-posterior patterning system was not established. Thus, POR function is indispensable for the proper regulation of RA levels and tissue distribution not only during early embryonic development but also in later morphogenesis and molecular patterning of the brain, abdominal/caudal region and limbs.

Participation of epoxygenase activation in saikogenin D-induced inhibition of prostaglandin E(2) synthesis

We examined the effect of saikogenin D on arachidonic acid metabolism in C6 rat glioma cells to clarify its anti-inflammatory mechanism. Incubation of C6 cells with saikogenin D for 20 min resulted in the inhibition of prostaglandin E(2) production and the accumulation of an arachidonic acid metabolite that was found to be 11,12-dihydroxyeicosatrienoic acid, a metabolite of 11,12-epoxyeicosatrienoic acid. C6 cells expressed rat epoxygenase mRNAs, CYP1A1, CYP2B1 and CYP2J3, which converted arachidonic acid to epoxyeicosatrienoic acids. 11,12-Epoxyeicosatrienoic acid inhibited A23187-induced prostaglandin E(2) production and SKF-525A, an inhibitor of epoxygenase, attenuated the saikogenin D-induced inhibition of prostaglandin E(2) production in C6 cells. Furthermore, 11,12-epoxyeicosatrienoic acid and 11,12-dihydroxyeicosatrienoic acid, but not saikogenin D, inhibited the activity of cyclooxygenase in a cell-free condition. These data suggest that saikogenin D activates epoxygenases that rapidly convert arachidonic acid to epoxyeicosanoids and dihydroxyeicosatrienoic acids, and then the metabolites secondarily inhibit prostaglandin E(2) production.

Differences in sensitivity of cultured rat brain neuronal and glial cytochrome P450 2E1 to ethanol

The expression of the cytochrome P450s (CYPs) may vary in the different brain cells depending on their specialization and the presence of different endogenous factors. The present study was initiated to investigate the expression and catalytic activity of the constitutive and inducible forms of CYP2E1, the major ethanol inducible CYP, in cultured rat brain neuronal and glial cells. These cells exhibited relatively two-fold higher activity of N-nitrosodimethylamine demethylase (NDMA-d) when compared with the liver enzyme. Pretreatment with ethanol revealed a significant time and concentration dependent induction in NDMA-d activity in both cell types. Western blot, immunocytochemistry and RT-PCR also indicated significant induction of CYP2E1 in the cultured brain cells. Interestingly, the neuronal cells exhibited greater magnitude of induction than the glial cells. The relatively higher degree of induction in cultures of neurons has indicated enhanced sensitivity of neurons to the inductive effects of ethanol. This enhanced induction of CYP2E1 in neuronal cells has indicated that like regional specificity, cell specificity also exists in the induction of CYP2E1 and other CYPs.

Cytochrome P450 4F subfamily: at the crossroads of eicosanoid and drug metabolism

The cytochrome P450 4F (CYP4F) subfamily has over the last few years come to be recognized for its dual role in modulating the concentrations of eicosanoids during inflammation as well as in the metabolism of clinically significant drugs. The first CYP4F was identified because it catalyzed the hydroxylation of leukotriene B(4) (LTB(4)) and since then many additional members of this subfamily have been documented for their distinct catalytic roles and functional significance. Recent evidence emerging in relation to the temporal change of CYP4F expression in response to injury and infection supports an important function for these isozymes in curtailing inflammation. Their tissue-dependent expression, isoform-based catalytic competence and unique response to the external stimuli imply a critical role for them to regulate organ-specific functions. From this standpoint variations in relative CYP4F levels in humans may have direct influence on the metabolic outcome through their ability to generate and/or degrade bioactive eicosanoids or therapeutic agents. This review covers the enzymatic characteristics and regulatory properties of human and rodent CYP4F isoforms and their physiological relevance to major pathways in eicosanoid and drug metabolism.

Expression of constitutive and inducible cytochrome P450 2E1 in rat brain

Studies initiated to investigate the expression of cytochrome P450 2E1 (CYP2E1) in rat brain demonstrated low but detectable protein and mRNA expression in control rat brain. Though mRNA and protein expression of CYP2E1 in brain was several fold lower as compared to liver, relatively high activity of N-nitrosodimethylamine demethylase (NDMA-d) was observed in control rat brain microsomes. Like liver, pretreatment with CYP2E1 inducers such as ethanol or pyrazole or acetone significantly increased the activity of brain microsomal NDMA-d. Kinetic studies also showed an increase in the Vmax and affinity (Km) of the substrate towards the brain enzyme due to increased expression of CYP2E1 in microsomes of brain isolated from ethanol pretreated rats. In vitro studies using organic inhibitors, specific for CYP2E1 and anti-CYP2E1 significantly inhibited the brain NDMA-d activity indicating that like liver, NDMA-d activity in rat brain is catalyzed by CYP2E1. Olfactory lobes exhibited the highest CYP2E1 expression and catalytic activity in control rats. Furthermore, several fold increase in the mRNA expression and activity of CYP2E1 in cerebellum and hippocampus while a relatively small increase in the olfactory lobes and no significant change in other brain regions following ethanol pretreatment have indicated that CYP2E1 induction maybe involved in selective sensitivity of these brain areas to ethanol induced free radical damage and neuronal degeneration.

Regional and cellular expression of CYP2D6 in human brain: higher levels in alcoholics

Cytochrome P450 (CYP) 2D6 is expressed in liver, brain and other extrahepatic tissues where it metabolizes a range of centrally acting drugs and toxins. As ethanol can induce CYP2D in rat brain, we hypothesized that CYP2D6 expression is higher in brains of human alcoholics. We examined regional and cellular expression of CYP2D6 mRNA and protein by RT-PCR, Southern blotting, slot blotting, immunoblotting and immunocytochemistry. A significant correlation was found between mean mRNA and CYP2D6 protein levels across 13 brain regions. Higher expression was detected in 13 brain regions of alcoholics (n = 8) compared to nonalcoholics (n = 5) (anovap < 0.0001). In hippocampus this was localized in CA1-3 pyramidal cells and dentate gyrus granular neurons. In cerebellum this was localized in Purkinje cells and their dendrites. Both of these brain regions, and these same cell-types, are known to be susceptible to alcohol damage. For one case, a poor metabolizer (CYP2D6*4/*4), there was no detectable CYP2D6 protein, confirming the specificity of the antibody used. These data suggest that in alcoholics elevated brain CYP2D6 expression may contribute to altered sensitivity to centrally acting drugs and to the mediation of neurotoxic and behavioral effects of alcohol.

The role of cytokines in the depression of CYP1A activity using cultured astrocytes as an in vitro model of inflammation in the central nervous system

The interaction and modulation of hepatic cytochrome P450 enzymes by infection and inflammation has been well described both in clinical settings and in animal models. Recent evidence found that inflammation in the central nervous system (CNS) leads to alterations in cytochrome P450 activity in both brain and liver. The bacterial endotoxin lipopolysaccharide (LPS) was used to induce an inflammatory response in cultured astrocytes as a model of CNS inflammation. This inflammatory response involves a range of immune mediators, such as acute phase cytokines, nitric oxide, prostanoid products, and reactive oxygen species. It is hypothesized that cytokines, released during inflammation, act to modulate the expression of specific isoforms of cytochrome P450 resulting in altered activity levels. High levels of the cytokines tumor necrosis factor-alpha and interleukin-1beta were released into culture medium after the addition of LPS to astrocyte cultures. When these same cytokines were added directly to the cultures, they also were able to modulate levels of CYP1A activity. The concurrent addition of dexamethasone to astrocytes blocked both the cytokine release and the alteration of CYP1A activity, thus supporting a role for these cytokines in this response. These results provide evidence suggesting an involvement of acute phase cytokines in mediating the LPS-induced depression of CYP1A activity in cultured astrocytes.

Alteration of drug biotransformation and elimination during infection and inflammation

During infection or inflammation, the expression of cytochrome P450 and its dependent biotransformation pathways are modified. This results in a change in the capacity of the liver to handle drugs and in alterations in the production and elimination of endogenous substances throughout the body. The majority of the CYP isoforms are modified at pre-translational steps in protein synthesis, and, in most cases, cytokines are involved as mediators of the response. Recent information suggests that inflammatory responses that are localized to the CNS cause a loss of CYP within the brain. This is accompanied by a parallel down-regulation of CYP in peripheral organs that is mediated by a signaling pathway between the brain and periphery. This review covers the loss that occurs in the major mammalian CYP families in response to infection/inflammation and the mediator pathways that are key to this response.

Cytochrome P450 2B (CYP2B)-mediated activation of methyl-parathion in rat brain extracts

The role of cytochrome P450 (CYP) and the CYP isoform involved in the activation of the widely used pesticide methyl-parathion (MePA) were investigated in rat brain extracts by measuring the effect of different CYP inhibitors on acetylcholinesterase (AChE) inhibition by MePA. Brain extracts provide a useful tool to study the activation mechanisms of organophosphorus compounds (OP) since they contain both the activating enzyme(s) and the molecular target for OP toxicity. As expected, in incubations of rat brain extract supplemented with NADPH, AChE activity was non-competitively inhibited by the presence of MePA, indicating that MePA was activated to its reactive metabolite methyl-paraoxon (MePO). Indeed, Vmax(app) decreased from 13.4 to 8.7 micromol thionitrobenzoic acid (TNB)/min per mg protein. MePA activation by rat brain extracts, as measured by the AChE inhibition produced by the presence of the pesticide in the incubation, was fully prevented by previously bubbling the incubation mix with CO, by the presence of monoclonal anti-rat CYP2B1/2B2 antibodies and by the addition of phenobarbital (PB), a CYP2B substrate. Interestingly, MePA showed a greater affinity for CYP2B than PB. CYP1A1 antibodies showed no effect on MePA activation. The presence of cytochrome P450 2B (CYP2B) in the rat brain extracts was confirmed by immunoblotting. These results demonstrate indisputably the responsibility of CYP2B in MePA activation in the rat brain in vitro, suggesting that metabolic activation of OP compounds in situ might be crucial for their organ specific toxicity to the central nervous system also in vivo.

Subchronic fluoxetine treatment induces a transient potentiation of amphetamine-induced hyperlocomotion: possible pharmacokinetic interaction

The results of the present study show that 5 days of systemic treatment with fluoxetine (5 mg/kg) resulted in an augmented locomotor response to amphetamine (0.5 mg/kg). This augmented response to amphetamine was observed 24 and 48 h, but not 5 days, after the cessation of fluoxetine treatment. Subchronic fluoxetine treatment also produced an increase in the brain concentration of amphetamine when rats were challenged with amphetamine 48 h, but not 5 days, after the cessation of fluoxetine treatment. Thus, the effect of subchronic fluoxetine in augmenting amphetamine-induced hyperactivity was consistent with the effect of subchronic fluoxetine in augmenting the amphetamine concentration in the brain. This pattern of results indicates that subchronic fluoxetine potentiates the response to amphetamine within a limited time-window, and that this potentiating effect is likely to be due to the reduced metabolism of amphetamine via the inhibition of cytochrome P450 by fluoxetine and/or its metabolite norfluoxetine.

Hepatic drug metabolism and immunostimulation

When host defence mechanisms are stimulated there is a concomitant decrease in cytochrome P450 based drug biotransformation and elimination. This has resulted in a number of clinically important unwanted drug responses in patients with infections or inflammatory responses. The loss in cytochrome P450 is predominantly an effect at the level of the gene expression and the majority of enzyme forms examined to date are involved. Although the effect occurs predominantly in the liver it has been recently shown that inflammatory responses in the brain also cause a loss of the same enzyme forms in that organ. The loss of cytochrome P450 in the brain in response to localised inflammation is accompanied by a similar loss in the liver. The decrease of cytochrome P450 and its dependent drug biotransformation is of concern whenever drugs are used in patients with infections or disease states with an inflammatory component.

Lipopolysaccharide evokes the modulation of brain cytochrome P4501A in the rat

The cytochrome P450 enzyme system is a multigene family of enzymes that is modulated in the liver during systemic inflammatory responses or during infection Several forms of the enzyme are expressed in discrete areas of the brain and likely play a critical role in the metabolism of drugs and endogenous chemicals in the central nervous system (CNS). Even though the brain responds to inflammation in a manner different from most tissues, we examined the possible modification of a major cytochrome P450 form (CYP1A) in the brain during inflammation confined to that organ. Total brain CYP1A activity, as measured by ethoxyresorufin dealkylase (EROD), was downregulated 24 and 48 h following the administration of a single dose of lipopolysaccharide (LPS). Regionally, a similar effect was determined in the cortex, hippocampus and the mid-brain but the activity in the cerebellum was unaffected. The examination of coronal brain sections using an antibody directed against CYP1A indicated that the enzyme was distributed in discrete cells of the hippocampus, thalamus and cortex and in the tanycytes surrounding the third ventricle. In each of these areas, the immunoreactivity was diminished in animals receiving LPS as compared to saline-treated animals. LPS also evoked the expression of the small molecular weight heat shock protein hsp27 throughout the brain indicating the development of an inflammatory response. These studies indicate that inflammation localized to the CNS causes an alteration in the levels and activity of a major cytochrome P450 form in the brain. This could have implications to the metabolism or activation of drugs and endogenous chemicals in the CNS during a disease state that features an inflammatory component.

Induction of rat brain and liver cytochrome P450 1A1/1A2 and 2B1/2B2 isoenzymes by deltamethrin

Deltamethrin, an α-cyano type II pyrethroid, administered orally (5, 10 and 15 mg/kg body weight for 7 consecutive days or at 5 mg/kg for further 15 and 21 days) to young albino Wistar rats (approximately 8 weeks old) produced a dose- and time-dependent increase in the activity of cytochrome P450-dependent 7-ethoxyresorufin-O-dealkylase (EROD) and 7-pentoxyresorufin-O-dealkylase (PROD) in rat liver and brain. However, significant induction in the enzyme activities was observed at higher doses or prolonged exposure. The magnitude of induction in rat liver microsomes was less at 15 mg/kg dose as compared to 10 mg/kg dose. Western blot analysis revealed a similar dose-related and time-dependent increase in the expression of P450 2B1/2B2 and 1A1 isoenzymes as indicated by the increased cross-reactivity of liver microsomes isolated from deltamethrin-treated animals with anti-P450 2B1/2B2 and 1A1. Inhibition of EROD and PROD observed after in vitro addition of anti-P450 2B1/2B2 and 1A1/1A2 or organic inhibitors, metyrapone and α-naphthoflavone, to the brain and liver microsomes of deltamethrin-pretreated animals (5 mg/kg×21 days), further provided support that the induction observed in the EROD and PROD activity in brain is due to the increased expression of P450 2B1/2B2 and 1A1/1A2, while, in the liver, isoenzymes other than these are also involved.

Expression and localisation of CYP2D enzymes in rat basal ganglia

P450 enzymes in the CYP2D subfamily have been suggested to contribute to the susceptibility of individuals in developing Parkinson's disease. We have used specific anti-peptide antisera and peroxidase immunohistochemistry to investigate the expression of CYP2D enzymes in the rat brain and some possible factors that may affect their regulation. In male Wistar rats, CYP2D1 was not detected in the basal ganglia or in any other brain region. CYP2D2 was weakly expressed within neurones of the subthalamic nucleus, substantia nigra and interpeduncular nucleus as well as in the hippocampus, dentate gyrus, red nucleus and pontine nucleus. CYP2D3 and CYP2D4 were absent from the basal ganglia, although moderate amounts of CYP2D3 were detected within fibres of the oculomotor root, and very low levels of CYP2D4 were present in white matter tracts. In contrast, CYP2D5 was extensively expressed in the basal ganglia, including neurones in the subthalamic nucleus, substantia nigra and interpeduncular nucleus, as well as other areas of the brain, including the ventral tegmental area, piriform cortex, hippocampus, dentate gyrus, medial habenular nucleus, thalamic nucleus and pontine nucleus. Lesioning of the nigro-striatal tract to cause almost a complete loss of tyrosine hydroxylase containing neurones in the substantia nigra, also reduced the number of neurones expressing CYP2D5 by 50%, indicating that CYP2D5 is expressed in dopaminergic neurones. Castration of pre-pubertal or adult Wistar rats had no effect on the number of CYP2D5-positive neurones in the substantia nigra. Although Dark Agouti rats lack hepatic CYP2D2, expression in the midbrain was similar to that of Wistar rats; furthermore, there was no difference in expression or distribution between male and female rats. In contrast to naive rats, extensive expression of CYP2D4 was found throughout the basal ganglia and in other brain nuclei in Wistar rats treated with not only clozapine, but also saline, suggesting that CYP2D4 may be induced as a result of mild stress. The function of CYP2D enzymes in the brain remains unknown, but their selective localisation suggests a physiological role in neuronal activity and in adaptation to abnormal situations.

Immunochemical detection of arylamine N-acetyltransferase during mouse embryonic development and in adult mouse brain

Arylamine N-acetyltransferases (NATs) are important in susceptibility to xenobiotic-induced disorders (e.g., drug-induced autoimmune disease, bladder cancer), but their role in endogenous metabolism is yet to be elucidated. The discovery that human NAT1 acts upon p-aminobenzoylgluatamate (p-ABG) to generate p-acetamidobenzoylglutamate (p-AABG), a major urinary metabolite of folic acid, suggests that human NAT1 may play a role in folic acid metabolism and hence in the normal development of the neural tube. In this study we examined the distribution of NAT in neuronal tissue from adult mice and embryos. Immunohistochemical staining of the adult mouse cerebellum revealed NAT2 (the mouse homologue of human NAT1) expression in the cell bodies and dendrites of Purkinje cells and in the neuroglia of the molecular layer. In embryos, NAT2 was detected in developing neuronal tissue on days 9.5, 11.5, and 13.5. It was expressed intensely in the nerual tube around the time of closure. The level of expression subsequently declined in the neuroepithelium but increased in glial cells. In addition, NAT2 was detected in the developing heart and gut. These findings demonstrate that the embryo itself expresses an enzyme which is involved in the metabolism of folic acid, so that the role played by both mother and embryo must be considered when examining the role of folic acid in embryonic development. These findings imply that polymorphisms in NAT genes could play a role in determining susceptibility to neural tube defects (NTD) and orofacial clefting, developmental disorders which can be prevented by dietary administration of folic acid.

Expression of CYP2M1, CYP2K1, and CYP3A27 in brain, blood, small intestine, and other tissues of rainbow trout

Expression of five constitutive forms of cytochrome P450 [(LMC1 (CYP2M1), LMC2 (CYP2K1), LMC3, LMC4, and LMC5 (CYP3A27)] in selected tissues from sexually immature 2-year old female and male rainbow trout (Oncorhynchus mykiss) were examined at the translational level by Western blot using polyclonal antibodies raised in rabbits against those purified trout hepatic P450s. Tissues examined were from brain, liver, muscle, blood, head kidney, trunk kidney, upper intestine, stomach, heart, and gonad (ovary or testis). The results showed that the liver was the major organ for expression of all the trout P450s studied. Trunk kidney was the secondary expression site except for LMC5. Selective translational expression of these P450 isoforms or similar proteins was observed for LCM1 and LMC5 in brain; for LMC2 and LMC5 in female upper intestine; and for LMC2 in blood plasma of the fish studied under the experimental and sampling conditions.

Expression, induction and regulation of the cytochrome P450 monooxygenase system in the rat glioma C6 cell line

The cytochrome P450 monooxygenase system consists of NADPH-cytochrome P450 reductase (P450 reductase) and cytochromes P450, which can catalyze the oxidation of a wide variety of endogenous and exogenous compounds. P450 reductase transfers reducing equivalents from NADPH to P450, which in turn catalyzes metabolic reactions. In previous studies, we have used the rat glioma C6 cell line as an in vitro model system and identified the presence of P450 reductase and of cytochrome P450 1A1, 1A2, 2A1, 2B1/2, 2C7, 2D1-5 and 2E1 by reverse transcription followed by polymerase chain reaction (RT-PCR). In C6 cells, the induction of P450 1A1 and 2B1/2 at mRNA level after BA (benzo(a)anthracene) or PB (phenobarbital) treatments was detected. In this study, analysis of microsomal preparations of glioma C6 cells was utilized to demonstrate the presence of P450 2B and P450 reductase at the protein level. ELISAs showed that PB induced P450 2B proteins 12-fold. These experiments further establish that the rat glioma C6 cell line contains an active cytochrome P450 monooxygenase system that can be induced by P450 inducers. We also found that the mRNAs of P450 1A1 and 2B1/2 from glioma C6 cells do not bind to the oligo(dT)-based separation techniques efficiently, suggesting that they may have very short poly(A) tails. The half-lives of P450 1A1 and 2B1/2 mRNA in glioma C6 cells are 1/10 and 1/3 of that in liver, respectively. This may partly contribute to the low expression level of P450s in glial cells. The induction of P450s by BA or PB did not change their mRNA half-lives, indicating the induction may be due to transcriptional regulation. In summary of this study, we believe the presence of the cytochrome P450 monooxygenase system in glial cells of the brain may be important in chemotherapy and carcinogenesis of brain tumors.

Expression and induction of cytochrome P-450 1A1 and P-450 2D subfamily in the rat glioma C6 cell line

The cytochrome P-450 (P-450) monooxygenase system can catalyze the oxidation of a wide variety of endogenous and exogenous compounds, including steroid hormones, fatty acids, drugs and pollutants. The functions of this system are as diverse as the substrates. Though this enzyme system has the highest level of activity in the liver, it is present in other tissues, including brain. In this study, we have established the rat glioma C6 cell line as an in vitro model system to examine the expression and induction of P-450 1A1 and the P-450 2D subfamily. Rat glioma C6 cells were treated with P-450 inducers phenobarbital (PB) or benzo[a]anthracene (BA). The presence of P-450 1A1 and 2D1-5 was detected by reverse transcription followed by polymerase chain reaction (RT-PCR) and confirmed by restriction enzyme digestion. The induction of P-450 1A1 and 2D1-5 was quantified using competitive PCR. Although P-450 2D1-5 do not seem to be affected by PB or BA treatment, tenfold induction of P-450 1A1 mRNA after BA treatment was detected. Western blot analysis of microsomal preparations of glioma C6 cells demonstrated the presence of P-450 1A1 at the protein level. ELISAs showed that BA induces P-450 1A1 proteins 7.3-fold. These experiments provide further evidence that the rat glioma C6 cell line contains an active cytochrome P-450 monooxygenase system which can be induced by P-450 inducers. In summary, we believe the presence of the cytochrome P-450 monooxygenase system in glial cells of the brain may be important in chemotherapy and carcinogenesis of brain tumors.