Xenobiotic metabolism in brain

Embryonic Exposure to Benzotriazole Ultraviolet Stabilizer 327 Alters Behavior of Rainbow Trout Alevin

Benzotriazole ultraviolet (UV) stabilizers (BUVSs) are used in great quantities during industrial production of a variety of consumer and industrial goods. As a result of leaching and spill, BUVSs are detectable ubiquitously in the environment. As of May 2023, citing concerns related to bioaccumulation, biomagnification, and environmental persistence, (B)UV(S)-328 was recommended to be listed under Annex A of the Stockholm Convention on Persistent Organic Pollutants. However, a phaseout of UV-328 could result in a regrettable substitution because the replacement chemical(s) could cause similar or unpredicted toxicity in vivo, relative to UV-328. Therefore, the influence of UV-327, a potential replacement of UV-328, was investigated with respect to early life development of newly fertilized rainbow trout embryos (Oncorhynchus mykiss), microinjected with environmentally relevant concentrations of UV-327. Developmental parameters (standard length), energy consumption (yolk area), heart function, blue sac disease, mortality, and behavior were investigated. Alevins at 14 days posthatching, exposed to 107 ng UV-327 g-1 egg, presented significant signs of hyperactivity; they moved on average 1.8-fold the distance and at 1.5-fold the velocity of controls. Although a substantial reduction in body burden of UV-327 was observed at hatching, it is postulated that UV-327, due to its lipophilic properties, interfered with neurological development and signaling from the onset of neurogenesis. If these results hold true across multiple taxa and species, a potential contributor to neurodevelopmental disorders might have been identified. These findings suggest that UV-327 poses an unknown hazard to rainbow trout embryos and alevins, rendering UV-327 a potential regrettable substitution to UV-328. However, a qualified statement on a regrettable substitution requires a comparative investigation on the teratogenic effects between the two BUVSs. Environ Toxicol Chem 2024;00:1-10. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

KUS121, a valosin-containing protein modulator, attenuates ischemic stroke via preventing ATP depletion

Reduced adenosine triphosphate (ATP) levels in ischemic stroke constitute an upstream contributor to neuronal cell death. We have recently created a small chemical, named Kyoto University Substance 121 (KUS121), which can reduce cellular ATP consumption. In this study, we examined whether KUS121 has neuroprotective effects in rodent cerebral ischemia models. We evaluated cell viability and ATP levels in vitro after oxygen glucose deprivation (OGD) in rat cortical primary neuronal cultures incubated with or without KUS121. We found that KUS121 protected neurons from cell death under OGD by preventing ATP depletion. We also used in vivo ischemic stroke models of transient distal middle cerebral artery occlusion in C57BL/6 and B-17 mice. Administration of KUS121 in these models improved functional deficits and reduced brain infarction volume after transient focal cerebral ischemia in both C57BL/6 and B-17 mice. These results indicate that KUS121 could be a novel type of neuroprotective drug for ischemic stroke.

Cell type-specific expression and localization of cytochrome P450 isoforms in tridimensional aggregating rat brain cell cultures

Within the Predict-IV FP7 project a strategy for measurement of in vitro biokinetics was developed, requiring the characterization of the cellular model used, especially regarding biotransformation, which frequently depends on cytochrome P450 (CYP) activity. The extrahepatic in situ CYP-mediated metabolism is especially relevant in target organ toxicity. In this study, the constitutive mRNA levels and protein localization of different CYP isoforms were investigated in 3D aggregating brain cell cultures. CYP1A1, CYP2B1/B2, CYP2D2/4, CYP2E1 and CYP3A were expressed; CYP1A1 and 2B1 represented almost 80% of the total mRNA content. Double-immunolabeling revealed their presence in astrocytes, in neurons, and to a minor extent in oligodendrocytes, confirming the cell-specific localization of CYPs in the brain. These results together with the recently reported formation of an amiodarone metabolite following repeated exposure suggest that this cell culture system possesses some metabolic potential, most likely contributing to its high performance in neurotoxicological studies and support the use of this model in studying brain neurotoxicity involving mechanisms of toxication/detoxication.

Expression of CYP1A1 and GSTP1 in human brain tumor tissues in Pakistan

Most of the exogenous and endogenous chemical compounds are metabolized by enzymes of xenobiotic processing pathways, including the phase I cytochrome p450 species. Carcinogens and their metabolites are generally detoxified by phase II enzymes like glutathione-S-transferases (GST). The balance of enzymes determines whether metabolic activation of pro-carcinogens or inactivation of carcinogens occurs. Under certain conditions, deregulated expression of xenobiotic enzymes may also convert endogenous substrates to metabolites that can facilitate DNA adduct formation and ultimately lead to cancer development. In this study, we aimed to test the association between deregulation of metabolizing genes and brain tumorigenesis. The expression profile of metabolizing genes CYP1A1 and GSTP1 was therefore studied in a cohort of 36 brain tumor patients and controls using Western blotting. In a second part of the study we analyzed protein expression of GSTs in the same study cohort by ELISA. CYP1A1 expression was found to be significantly high (p<0.001) in brain tumor as compared to the normal tissues, with ~4 fold (OR=4, 95%CI=0.43-37) increase in some cases. In contrast, the expression of GSTP1 was found to be significantly low in brain tumor tissues as compared to the controls (p<0.02). This down regulation was significantly higher (OR=0.05, 95%CI=0.006-0.51; p<0.007) in certain grades of lesions. Furthermore, GSTs levels were significantly down-regulated (p<0.014) in brain tumor patients compared to controls. Statistically significant decrease in GST levels was observed in the more advanced lesions (III-IV, p<0.005) as compared to the early tissue grades (I-II). Thus, altered expression of these xenobiotic metabolizing genes may be involved in brain tumor development in Pakistani population. Investigation of expression of these genes may provide information not only for the prediction of individual cancer risk but also for the prevention of cancer.

Exposure to benzidine caused apoptosis and malformation of telencephalon region in zebrafish

Exposure to benzidine has been known to induce human cancers, particularly bladder carcinomas. In this study, the zebrafish model was used to investigate the developmental toxicity of benzidine. Embryos at 6 h postfertilization (hpf) that were exposed to benzidine exhibited embryonic death in a dose- and time-dependent manner. Benzidine induced malformations in zebrafish, such as small brain development, shorter axes, and a slight pericardial edema. High concentrations (50, 100, and 200 µM) of benzidine triggered widespread apoptosis in the brain and dorsal neurons, as evidenced by acridine orange and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assays. Real-time polymerase chain reaction analysis also showed that benzidine treatment affected p53, bax, and noxa expression. Decreases in specific brain markers, such as emx1 in the telencephalon, ngn1 in differentiated neurons, and otx2 in the midbrain, were observed in benzidine-treated embryos at 24 hpf. Conversely, no overt changes to pax2.1 expression in the midbrain-hindbrain boundary were found. Moreover, the use of Tg(HuC:GFP) zebrafish showed that benzidine caused a malformation of the telencephalon region. Our findings show that benzidine exposure triggers widespread apoptosis in the zebrafish brain and dorsal neurons, resulting in the development of an abnormal telencephalon.

Neurobehavioral toxicity of a repeated exposure (14 days) to the airborne polycyclic aromatic hydrocarbon fluorene in adult Wistar male rats

Fluorene is one of the most abundant polycyclic aromatic hydrocarbons in air and may contribute to the neurobehavioral alterations induced by the environmental exposure of humans to PAHs. Since no data are available on fluorene neurotoxicity, this study was conducted in adult rats to assess the behavioral toxicity of repeated fluorene inhalation exposure. Male rats (n = 18/group) were exposed nose-only to 1.5 or 150 ppb of fluorene 6 hours/day for 14 consecutive days, whereas the control animals were exposed to non-contaminated air. At the end of the exposure, animals were tested for activity and anxiety in an open-field and in an elevated-plus maze, for short-term memory in a Y-maze, and for spatial learning in an eight-arm maze. The results showed that the locomotor activity and the learning performances of the animals were unaffected by fluorene. In parallel, the fluorene-exposed rats showed a lower level of anxiety than controls in the open-field, but not in the elevated-plus maze, which is probably due to a possible difference in the aversive feature of the two mazes. In the same animals, increasing blood and brain levels of fluorene monohydroxylated metabolites (especially the 2-OH fluorene) were detected at both concentrations (1.5 and 150 ppb), demonstrating the exposure of the animals to the pollutant and showing the ability of this compound to be metabolized and to reach the cerebral compartment. The present study highlights the possibility for a 14-day fluorene exposure to induce some specific anxiety-related behavioral disturbances, and argues in favor of the susceptibility of the adult brain when exposed to volatile fluorene.

Modulation of benzo[a]pyrene induced neurotoxicity in female mice actively immunized with a B[a]P-diphtheria toxoid conjugate

Benzo[a]pyrene (B[a]P) is a small molecular weight carcinogen and the prototype of polycyclic aromatic hydrocarbons (PAHs). While these compounds are primarily known for their carcinogenicity, B[a]P and its metabolites are also neurotoxic for mammalian species. To develop a prophylactic immune strategy against detrimental effects of B[a]P, female Balb/c mice immunized with a B[a]P-diphtheria toxoid (B[a]P-DT) conjugate vaccine were sub-acutely exposed to 2mg/kg B[a]P and behavioral performances were monitored in tests related to learning and memory, anxiety and motor coordination. mRNA expression of the NMDA receptor (NR1, 2A and 2B subunits) involved in the above behavioral functions was measured in 5 brain regions. B[a]P induced NMDA1 expression in three (hippocampus, amygdala and cerebellum) of five brain regions investigated, and modulated NMDA2 in two of the five brain regions (frontal cortex and cerebellum). Each one of these B[a]P-effects was reversed in mice that were immunized against this PAH, with measurable consequences on behavior such as anxiety, short term learning and memory. Thus active immunization against B[a]P with a B[a]P-DT conjugate vaccine had a protective effect and attenuated the pharmacological and neurotoxic effects even of high concentrations of B[a]P.

Ontogeny of mammalian metabolizing enzymes in humans and animals used in toxicological studies

It is well recognized that expression of enzymes varies during development and growth. However, an in-depth review of this acquired knowledge is needed to translate the understanding of enzyme expression and activity into the prediction of change in effects (e.g. kinetics and toxicity) of xenobiotics with age. Age-related changes in metabolic capacity are critical for understanding and predicting the potential differences resulting from exposure. Such information may be especially useful in the evaluation of the risk of exposure to very low (µg/kg/day or ng/kg/day) levels of environmental chemicals. This review is to better understand the ontogeny of metabolizing enzymes in converting chemicals to either less-toxic metabolite(s) or more toxic products (e.g. reactive intermediate[s]) during stages before birth and during early development (neonate/infant/child). In this review, we evaluated the ontogeny of major "phase I" and "phase II" metabolizing enzymes in humans and commonly used experimental animals (e.g. mouse, rat, and others) in order to fill the information gap.

Differential subcellular distribution and colocalization of the microsomal and soluble epoxide hydrolases in cultured neonatal rat brain cortical astrocytes

The microsomal epoxide hydrolase (mEH) and soluble epoxide hydrolase (sEH) enzymes exist in a variety of cells and tissues, including liver, kidney, and testis. However, very little is known about brain epoxide hydrolases. Here we report the expression, localization, and subcellular distribution of mEH and sEH in cultured neonatal rat cortical astrocytes by immunocytochemistry, subcellular fractionation, Western blotting, and radiometric enzyme assays. Our results showed a diffuse immunofluorescence pattern for mEH, which colocalized with the astroglial cytoskeletal marker glial fibrillary acidic protein (GFAP). The GFAP-positive cells also expressed sEH, which was localized mainly in the cytoplasm, especially in and around the nucleus. Western blot analyses revealed a distinct protein band with a molecular mass of approximately 50 kDa, the signal intensity of which increased about 1.5-fold in the microsomal fraction over the whole-cell lysate and other subcellular fractions. The polyclonal anti-human sEH rabbit serum recognized a protein band with a molecular mass similar to that of the affinity-purified sEH protein (approximately 62 kDa), the signal intensity of which increased over 1.7-fold in the 105,000g supernatant fraction over the cell lysate. Furthermore, the corresponding enzyme activities measured by using mEH- and sEH-selective substrates generally corroborated the immunocytochemical and Western blotting data. These results suggest that rat brain cortical astrocytes differentially coexpress mEH and sEH enzymes. The differential subcellular localization of mEH and sEH may play a role in the cerebrovascular functions that are known to be affected by brain-derived vasoactive epoxides.

Sequence alterations within CYP7B1 implicate defective cholesterol homeostasis in motor-neuron degeneration

The hereditary spastic paraplegias (HSPs) are a genetically and clinically heterogeneous group of upper-motor-neuron degenerative diseases characterized by selective axonal loss in the corticospinal tracts and dorsal columns. Although numerous mechanisms involving defective subcellular transportation, mitochondrial malfunction, and increased oxidative stress have been proposed, the pathogenic basis underlying the neuronal loss is unknown. We have performed linkage analysis to refine the extent of the SPG5 disease locus and conducted sequence analysis of the genes located within this region. This identified sequence alterations in the cytochrome P450-7B1 (CYP7B1) associated with this pure form of HSP. In the liver, CYP7B1 offers an alternative pathway for cholesterol degradation and also provides the primary metabolic route for the modification of dehydroepiandrosterone neurosteroids in the brain. These findings provide the first direct evidence of a pivotal role of altered cholesterol metabolism in the pathogenesis of motor-neuron degenerative disease and identify a potential for therapeutic intervention in this form of HSP.

Metabolization of Porphyrinogenic Agents in Brain: Involvement of the Phase I Drug Metabolizing System. A Comparative Study in Liver and Kidney

(1) We evaluated the involvement of brain mitochondrial and microsomal cytochrome P-450 in the metabolization of known porphyrinogenic agents, with the aim of improving the knowledge on the mechanism leading to porphyric neuropathy. We also compared the response in brain, liver and kidney. To this end, we determined mitochondrial and microsomal cytochrome P-450 levels and the activity of NADPH cytochrome P-450 reductase. (2) Animals were treated with known porphyrinogenic drugs such as volatile anaesthetics, allylisopropylacetamide, veronal, griseofulvin and ethanol or were starved during 24 h. Cytochrome P-450 levels and NADPH cytochrome P-450 reductase activity were measured in mitochondrial and microsomal fractions from the different tissues. (3) Some of the porphyrinogenic agents studied altered mitochondrial cytochrome P-450 brain but not microsomal cytochrome P-450. Oral griseofulvin induced an increase in mitochondrial cytochrome P-450 levels, while chronic Isoflurane produced a reduction on its levels, without alterations on microsomal cytochrome P-450. Allylisopropylacetamide diminished both mitochondrial and microsomal cytochrome P-450 brain levels; a similar pattern was detected in liver. Mitochondria cytochrome P-450 liver levels were only diminished after chronic Isoflurane administration. In kidney only mitochondrial cytochrome P-450 levels were modified by veronal; while in microsomes, only acute anaesthesia with Enflurane diminished cytochrome P-450 content. (4) Taking into account that delta-aminolevulinic acid would be responsible for porphyric neuropathy, we investigated the effect of acute and chronic delta-aminolevulinic acid administration. Acute delta-aminolevulinic acid administration reduced brain and liver cytochrome P-450 levels in both fractions; chronic delta-aminolevulinic acid administration diminished only liver mitochondrial cytochrome P-450. (5) Brain NADPH cytochrome P-450 reductase activity in animals receiving allylisopropylacetamide, dietary griseofulvin and delta-aminolevulinic acid showed a similar profile as that for total cytochrome P-450 levels. The same response was observed for the hepatic enzyme. (6) Results here reported revealed differential tissue responses against the xenobiotics assayed and give evidence on the participation of extrahepatic tissues in porphyrinogenic drug metabolization. These studies have demonstrated the presence of the integral Phase I drug metabolizing system in the brain, thus, total cytochrome P-450 and associated monooxygenases in brain microsomes and mitochondria would be taken into account when considering the xenobiotic metabolizing capability of this organ.

An alternatively spliced cytochrome P4501A1 in human brain fails to bioactivate polycyclic aromatic hydrocarbons to DNA-reactive metabolites

CYP1A1, a cytochrome P450 enzyme, metabolizes polycyclic aromatic hydrocarbons to genotoxic metabolite(s) that bind to DNA and initiate carcinogenesis. RT-PCR amplification of the complete open reading frame of CYP1A1 generated an amplicon of 1593 bp having deletion of 87 bp of exon-6 that translated into functional P450 enzyme. Unlike wild type CYP1A1, exon 6 del CYP1A1 did not metabolize polycyclic aromatic hydrocarbons such as, benzo(a)pyrene to genotoxic, ultimate carcinogens that form DNA adducts. Exon 6 del CYP1A1 metabolized ethoxyresorufin (the classical substrate for CYP1A1) less efficiently compared with wild type CYP1A1 while pentoxy and benzyloxyresorufin (classical substrates for CYP2B) were dealkylated more efficiently. In silico docking showed alteration of the substrate access channel in exon 6 del CYP1A1 such that benzo(a)pyrene does not bind in any orientation that would permit the formation of carcinogenic metabolites. Genotyping revealed that the splice variant was not generated due to differences in genomic DNA sequence and the variant was present only in brain but not in liver, kidney, lung, or heart from the same individual. We provide evidence that unique P450 enzymes, generated by alternate splicing in a histiospecific manner can modify genotoxic potential of carcinogens such as benzo(a)pyrene by altering their biotransformation pathway.

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.

Neuroleptic drugs in the human brain: clinical impact of persistence and region-specific distribution

After discontinuation of neuroleptic agents, their effects are still present for a long time. The exact underlaying mechanisms are still unclear. In two previous studies we measured the concentrations and region-specific distribution of haloperidol (Kornhuber et al. 1999) and levomepromazine (Kornhuber et al. 2006) in postmortem human brain tissues. The aim of the present paper is to compare the results of these two studies. Even after short-term treatment, haloperidol and levomepromazine concentrations reach high levels in human brain tissue. Haloperidol concentrations in brain tissue are 10-30 times higher than the optimum serum concentrations in the treatment of schizophrenia. The brain-to-blood concentration ratio of levomepromazine is about 10. The estimated elimination half-life of these drugs in brain tissue are 6.8 days (haloperidol), 7.9 days (levomepromazine) and 27.8 days for the metabolite desmethyl-levomepromazine, respectively. After two half-lives (about 2 weeks), a considerable amount of drug remains in brain tissue. Haloperidol concentrations appeared to be homogeneously distributed across different brain areas, whereas levomepromazine shows a region-specific distribution, with highest values in the basal ganglia. The persistence of neuroleptic drugs in the human brain might explain their prolonged effects and side effects. The region-specific distribution of levomepromazine may increase our understanding of both the preferential toxicity of neuroleptic drugs against basal ganglia structures and higher basal ganglia volumes in patients treated with neuroleptics.

Region specific distribution of levomepromazine in the human brain

OBJECTIVE

The aim of this study was to examine concentrations of levomepromazine and its metabolite desmethyl-levomepromazine in different regions of human brain and in relationship to drug-free time.

METHODS

Drug concentrations were measured in up to 43 regions of 5 postmortem human brains of patients previously treated with levomepromazine. To enable statistical comparison across brain regions several smaller brain areas were put together to form larger brain areas (cortex cerebri, limbic system, cerebellum, basal ganglia, thalamus). Mean values of drug concentrations in these larger brain areas were used in a repeated measurement ANOVA to analyze for region specific distribution. The elimination half-life in brain tissue was estimated with a NONMEM population kinetic analysis using the mean value of all brain regions of an individual case.

RESULTS

Levomepromazine and desmethyl-levomepromazine appear to accumulate in human brain tissue relative to blood. Mean concentrations differed largely between individual brains, in part due to differences in dose of drug, duration of treatment and drug-free time before death. There was an apparent region-specific difference in levomepromazine concentrations with highest values in the basal ganglia (mean 316 ng/g) and lowest values in the cortex cerebri (mean 209 ng/g). The elimination half-life from brain tissue is longer than from blood and was calculated to be about one week. Similar results were obtained with desmethyl-levomepromazine.

CONCLUSIONS

Levomepromazine shows a region-specific distribution in the human brain with highest values in the basal ganglia. This might be the consequence of low expression of the metabolic enzyme Cyp2D6 in the basal ganglia. If this finding is true also for other neuroleptic drugs it might increase our understanding of preferential toxicity of neuroleptic drugs against basal ganglia structures and higher volumes of basal ganglia of neuroleptic-treated patients. Furthermore, patients exposed to levomepromazine cannot be considered to be free of residual effects of the drug for a number of weeks after withdrawal.

Immunohistochemical detection of the human cytochrome P4507B1: production of a monoclonal antibody after cDNA immunization

The cytochrome P4507B1 (P4507B1) is responsible for the 7alpha-hydroxylation of dehydroepiandrosterone (DHEA) and other 3beta-hydroxysteroids in the brain and other organs. The cDNA of human P4507B1 was used for DNA immunization of mice. The best responding mouse led to the production of monoclonal antibodies (mAbs). The clone D16-37 produced an IgM specific for P4507B1 with no cross-reaction with other human P450s. This antibody permitted the immunohistochemical detection of P4507B1 in slices of human hippocampus. P4507B1 was expressed in neurons only. This new tool will be used for the extensive examination of the P4507B1 presence and determination of its levels in slices of human normal and diseased brain and in other human tissues.

In silico analysis of gene expression profiles in the olfactory mucosae of aging senescence-accelerated mice

We utilized high-density Affymetrix oligonucleotide arrays to investigate gene expression in the olfactory mucosae of near age-matched aging senescence-accelerated mice (SAM). The senescence-prone (SAMP) strain has a significantly shorter lifespan than does the senescence-resistant (SAMR) strain. To analyze our data, we applied biostatistical methods that included a correlation analysis to evaluate sources of methodologic and biological variability; a two-sided t-test to identify a subpopulation of Present genes with a biologically relevant P-value <0.05; and a false discovery rate (FDR) analysis adjusted to a stringent 5% level that yielded 127 genes with a P-value of <0.001 that were differentially regulated in near age-matched SAMPs (SAMP-Os; 13.75 months) compared to SAMRs (SAMR-Os, 12.5 months). Volcano plots related the variability in the mean hybridization signals as determined by the two-sided t-test to fold changes in gene expression. The genes were categorized into the six functional groups used previously in gene profiling experiments to identify candidate genes that may be relevant for senescence at the genomic and cellular levels in the aging mouse brain (Lee et al. [2000] Nat Genet 25:294-297) and in the olfactory mucosa (Getchell et al. [2003] Ageing Res Rev 2:211-243), which serves several functions that include chemosensory detection, immune barrier function, xenobiotic metabolism, and neurogenesis. Because SAMR-Os and SAMP-Os have substantially different median lifespans, we related the rate constant alpha in the Gompertz equation on aging to intrinsic as opposed to environmental mechanisms of senescence based on our analysis of genes modulated during aging in the olfactory mucosa.

Immunohistochemical evidence for the expression and induction of paraoxonase in rat liver, kidney, lung and brain tissue. Implications for its physiological role

Studies on the localization of paraoxonases (PON's) are of interest because of its involvement in both the detoxication of activated organophosphorus pesticides and in the prevention of peroxidative damage to phospholipids and cholesteryl-esters in LDL and HDL particles and cell membranes during the atherogenic process. In the present study, we have investigated the cellular localization of PON1 by immunohistochemistry in different rat tissues. The protein was mainly detected in the endothelial lining of every tissue studied (liver, kidney, lung and brain). Besides, it was found in hepatocytes from the centrolobular region of the liver, in the glomeruli and basal pole of the proximal convoluted tubule of the kidney, in cells from bronchiolar epithelium and type I pneumocytes of the lung, and in leptomeningeal cells, ependymal cells and ventricular side of choroid plexus cells of the brain. However, neurons and glia lacked immunostaining. After 3-methylcholanthrene induction an increase in the intensity of immunostaining was observed in the same areas, as well as an additional staining in midzonal hepatocytes. On the basis of the tissue distribution observed for PON1, it is proposed that this enzyme might have a function related to the inactivation of oxidative stress by-products (either at a cellular level or blood-vessel wall) and other environmental chemicals. At present it has not yet been established whether the paraoxonase detected in the various tissues is truly a product of the PON1 gene or could represent products of the PON2 or PON3 genes.

In vivo steady-state pharmacokinetic outcome following clinical and toxic doses of racemic citalopram to rats

The thymoleptic drug citalopram (CIT) belongs to the selective serotonin reuptake inhibitors (SSRIs) and is today extensively used in psychiatry. Further clarification of the enantiomer-selective distribution of racemic CIT in both clinical and toxic doses is highly warranted. By a steady-state in vivo paradigm, rats underwent chronic systemic exposure for 10 days by using osmotic pumps and the total as well as the individual distributions of the S- and R-enantiomers of CIT, and its metabolites in serum and two different brain regions, were analysed. In serum, the S/R ratios in the groups treated with 10, 20, or 100 mg kg(-1) day(-1) were 0.94, 0.83, and 0.34, respectively. The ratios were almost the same in the brain regions. In the group treated with 100 mg kg(-1) day(-1), the serum and brain total CIT levels were found to be 20 times and 6 - 8 times higher than in the rats treated with 10 or 20 mg kg(-1) day(-1), respectively. In all groups, the CIT levels were higher in brain tissue as compared to serum. In a spontaneous open-field behavioural test, a correlation between clinical and toxic drug concentrations was observed. In conclusion, the R-enantiomer was present in an increased proportion compared with the S-enantiomer when higher steady-state CIT concentration was prevailing. This is of particular interest, since the S-enantiomer is responsible for the inhibition of serotonin reuptake in vitro. The present data may be of importance, as full understanding on where different racemic or enantiomeric drug effects of CIT and its main metabolites are unravelled.

Regional and cellular induction of nicotine-metabolizing CYP2B1 in rat brain by chronic nicotine treatment

In the rat, nicotine is metabolized to cotinine primarily by hepatic cytochrome P450 (CYP) 2B1. This enzyme is also found in other organs such as the lung and the brain. Hepatic nicotine metabolism is unaltered after nicotine exposure; however, nicotine may regulate CYP2B1 in other tissues. We hypothesized that nicotine induces its own metabolism in brain by increasing CYP2B1. Male rats were treated with nicotine (0.0, 0.1, 0.3, or 1.0 mg base/kg in saline) s.c. daily for 7 days. CYP2B1 mRNA and protein were assayed in the brain and liver by reverse transcriptase-polymerase chain reaction (RT-PCR), immunoblotting, and immunocytochemistry. In control rats, CYP2B1 mRNA and protein expression were brain region- and cell-specific. CYP2B1 was not induced in the liver, but CYP2B1 mRNA and protein showed dose-dependent, region- and cell-specific patterns of induction across brain regions. At 1.0 mg nicotine/kg, the largest increase in protein was in the brain stem (5.8-fold, P < 0.05) with a corresponding increase in CYP2B1 mRNA (7.6-fold, P < 0.05). Induction of CYP2B1 was also observed in the frontal cortex, striatum, and olfactory tubercle. Immunocytochemistry showed that induction was restricted principally to neurons. These data indicate that nicotine may alter its own metabolism in the brain through transcriptional regulation, perhaps contributing to central tolerance to the effects of nicotine. CYP2B1 and its human homologue CYP2B6 also activate tobacco smoke procarcinogens such as NNK [4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone]. Highly localized increases in CYP2B could result in increased mutagenesis. These data suggest roles for nicotine-induced CYP2B in central metabolic tolerance, nicotine-induced neurotoxicity, neuroplasticity, and carcinogenesis.

Human brain cytochrome P450 1B1: immunohistochemical localization in human temporal lobe and induction by dimethylbenz(a)anthracene in astrocytoma cell line (MOG-G-CCM)

CYP1B1, a new member of human cytochrome P450 family 1, is involved in the xenobiotic detoxification metabolism and possibly activation of numerous procarcinogens and promutagens. Localization of CYP1B1 in human temporal lobe and its induction in astrocytoma cell line (MOG-G-CCM) by 7,12-dimethylbenz(a)anthracene (DMBA) was investigated using antibodies against human CYP1B1. A single band of approximately 58 kDa size in both human temporal lobe and in MOG-G-CCM was detected by Western blot analysis. Treatment of MOG-G-CCM cells with DMBA resulted in approximately 2.8-fold induction of CYP1B1. CYP1B1 immunoreactivity was detected at the blood-brain interface areas of the temporal lobe as evidenced by co-localization with CD34 antigen. These results suggest that this enzyme may be important in brain xenobiotic metabolism acting as an enzymatic barrier.

Occupation of the cytochrome P450 substrate pocket by diverse compounds at general anesthesia concentrations

Each of a diverse array of compounds, at concentrations reported to effect general anesthesia, when added to liver microsomes, forms a complex with cytochromes P450 to generate, with reference to a cuvette containing microsomes only, a characteristic absorbance-difference spectrum. This spectrum results from a change in the electron-spin state of the heme iron atom induced upon entry by the anesthetic molecule into the enzyme catalytic pocket. The difference spectrum, representing the anesthetic-P450 complex, is characteristic of substances that are substrates for the enzyme. For the group of compounds as a whole, the magnitudes of the absorbance-difference spectra vary only about twofold, although the anesthetic potencies vary by several orders of magnitude. The dissociation constants (Ks), calculated from absorbance data and representing affinities of the anesthetics for P450, agree closely with the respective EC50 (concentration that effects anesthesia in 50% of individuals) values, and with the respective Ki (concentration that inhibits P450 catalytic activities half-maximally) values reported by us previously. The absorbance complex resulting from the occupation of the catalytic pocket by endogenous substrates, androstenedione and arachidonic acid, is inhibited, competitively, by anesthetics. Occupation of and perturbation of the heme catalytic pocket by anesthetic, as monitored by the absorbance-difference spectrum, is rapidly reversible. The presumed in vivo consequences of perturbation by general anesthetics of heme proteins is suppression of the generation of chemical signals that determine cell sensitivity and response.

Cytochrome P450 1B1 mRNA in the human central nervous system

AIMS

To study the expression of CYP1B1 in a variety of human and rat cell lines as a means of identifying a new tool for the investigation of gene regulation. In addition, to identify the expression of cytochrome P450 1B1 (CYP1B1) in different regions of the central nervous system (CNS).

METHODS

Reverse transcription-polymerase chain reaction followed by cloning and sequencing were used to detect the expression of CYP1B1 in human cell lines. Poly A+ mRNA from the human spinal cord and from different brain regions was analysed using a CYP1B1 probe labelled with 32PdCTP.

RESULTS

Expression of CYP1B1 was shown in a human astrocytoma cell line (MOG-G-CCM). CYP1B1 mRNA was expressed in a variety of regions of the CNS but with a distinct regional specificity. Expression was highest in the putamen.

CONCLUSIONS

The expression of CYP1B1 in a human astrocytoma enables this cell line to be used in further studies of regulation and function of this gene. The demonstration that CYP1B1 mRNA is expressed in a variety of regions of the CNS suggests a role for this gene in brain and spinal cord metabolism. The regional specificity of expression might explain the focal damage of certain human neurodegenerative diseases.

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.

Metabolism of (-)-(S)-nicotine by guinea pig and rat brain: identification of cotinine

Since the brain is the major site of pharmacological activity of nicotine, it was of interest to investigate the metabolism of nicotine by this organ. We now report our findings using guinea pig and rat brain as the enzyme source. Whole brains were removed and washed with isotonic KCl, blotted dry and cut into small pieces. The tissue was weighed and homogenized in pH 7.4 Tris-KCl buffer, 2 ml/g tissue. Incubations were carried out using 0.5 ml of brain homogenate and 0.1-1 mumol of nicotine at 37 degrees C. The reactions were terminated by freezing at -80 degrees C. The samples were extracted and analyzed by capillary GC with nitrogen-phosphorus detection. Cotinine was detected as the major metabolite and its identity confirmed by GC-MS. Cotinine formation may contribute to the detoxication pathway of nicotine and may be important in controlling nicotine levels in the brain. Furthermore, the conversion of nicotine to cotinine involves the intermediacy of nicotine-delta [1'(5')]-iminium ion, which is an alkylating agent. This finding supports the concept that reactive intermediates may play a role in the pharmacology and toxicology of nicotine.

Regulation of CYP3A9 gene expression by estrogen and catalytic studies using cytochrome P450 3A9 expressed in Escherichia coli

Sexual dimorphism in the expression of CYP3A9, a novel form of CYP3A from rat brain, is shown for the first time in rat brain as well as in rat liver. CYP3A9 expression is female specific in rat liver as judged by its 10-fold higher expression in females than in males. CYP3A9 gene expression was inducible by estrogen treatment both in male and in female rats. Ovariectomy of adult female rats elicited a drastic reduction on the mRNA level of CYP3A9 which could be fully restored by estrogen replacement. These results suggest that estrogen may play an important role in the female-specific expression of the CYP3A9 gene. P450 3A9 recombinant protein was expressed in Escherichia coli by means of the pCWOri+ expression vector and the MALLLAVF amino terminal sequence modification. This construct gave a high level of expression (130 nmol P450 3A9/liter culture) and the recombinant protein of the modified P450 3A9 was purified to electrophoretic homogeneity with a specific content of 10.1 nmol P450/mg protein from solubilized fractions through two chromatographic steps. The purified P450 3A9 protein was active in the metabolism of imipramine, erythromycin, benzphetamine, and ethylmorphine as well as 17beta-estradiol in a reconstituted system containing lipid and rat NADPH-P450 reductase. Of special interest is the finding that P450 3A9 can catalyze the formation of desipramine with a turnover number of 4.9 nmol/min/nmol P450, suggesting the possible involvement of this isoform in the metabolism of imipramine in brain. Optimal reconstitution conditions for P450 3A9 activities required a lipid mixture (1:1:1 mixture of L-alpha-dilauroyl phosphatidylcholine, L-alpha-dioleoyl phosphatidylcholine, and phosphatidylserine) and GSH.