Mammalian cytochromes P450—Importance of tissue specificity

CYP1A and POR gene mediated mitochondrial membrane damage induced by carbon nanoparticle in human mesenchymal stem cells

Nanoparticles (NPs) can cause respiratory and cardiovascular problems, furthermore small carboxyl polystyrene NPs induce hemolysis, activate platelets and induce inflammation in human blood. Carbon nanoparticles (CNPs) are known to interfere with cellular metabolism, specific cellular functions and moreover may cause cellular toxicity. We aimed to study the influence of CNPs on oxidative stress, mitochondrial membrane damage and intracellular gene expression in human mesenchymal stem cells (hMSCs). CNPs cause a dose and time dependent growth inhibition in hMSCs at a dose range from 50 to 400μg/mL. Exposure of CNPs toxic doses viz., 50μg/mL (D1) and 100μg/mL (D2) decreased intracellular mitochondrial membrane potential compared to control. CNPs treated cells were found to lose their morphology due to cell membrane damage have been confirmed by propidium iodide staining and fluorescence microscopic analysis. Oxidative stress responsive genes like GSTM3 and GSR1 expression have increased a fold when compared to control, interim there is no change were observed in SOD and GPx. We found an increased expression of CYP1A and POR genes by at least 2- fold, which is involved in mitochondrial trans-membrane potential. In conclusion, routine and high exposure of CNPs to hMSCs increased oxidative stress and mitochondrial membrane damage.

Selective induction of tumor cell apoptosis by a novel P450-mediated reactive oxygen species (ROS) inducer methyl 3-(4-nitrophenyl) propiolate

Induction of tumor cell apoptosis has been recognized as a valid anticancer strategy. However, therapeutic selectivity between tumor and normal cells has always been a challenge. Here, we report a novel anti-cancer compound methyl 3-(4-nitrophenyl) propiolate (NPP) preferentially induces apoptosis in tumor cells through P450-catalyzed reactive oxygen species (ROS) production. A compound sensitivity study on multiple cell lines shows that tumor cells with high basal ROS levels, low antioxidant capacities, and p53 mutations are especially sensitive to NPP. Knockdown of p53 sensitized non-transformed cells to NPP-induced cell death. Additionally, by comparing NPP with other ROS inducers, we show that the susceptibility of tumor cells to the ROS-induced cell death is influenced by the mode, amount, duration, and perhaps location of ROS production. Our studies not only discovered a unique anticancer drug candidate but also shed new light on the understanding of ROS generation and function and the potential application of a ROS-promoting strategy in cancer treatment.

Mitochondrial decay in ageing: 'Qi-invigorating' schisandrin B as a hormetic agent for mitigating age-related diseases

1. The mitochondrial free radical theory of ageing (MFRTA) proposes a primary role for mitochondrial reactive oxygen species (ROS) in the ageing process. The reductive hot spot hypothesis of mammalian ageing serves as a supplement to the MFRTA by explaining how the relatively few cells that have lost oxidative phosphorylation capacity due to mitochondrial DNA mutations can be toxic to the rest of the body and result in the development of age-related diseases. 2. Schisandrin B (SchB), which can induce both a glutathione anti-oxidant and a heat shock response via redox-sensitive signalling pathways, is a hormetic agent potentially useful for increasing the resistance of tissues to oxidative damage. The enhanced cellular/mitochondrial anti-oxidant status and heat shock response afforded by SchB can preserve the structural and functional integrity of mitochondria, suggesting a potential role for SchB in ameliorating age-related diseases. 3. Future studies will focus on investigating whether SchB can produce the hormetic response in humans.

Metabolic and Pharmacokinetic Differentiation of STX209 and Racemic Baclofen in Humans

STX209 is an exploratory drug comprising the single, active R-enantiomer of baclofen which is in later stage clinical trials for the treatment of fragile x syndrome (FXS) and autism spectrum disorders (ASD). New clinical data in this article on the metabolism and pharmacokinetics of the R- and S-enantiomers of baclofen presents scientific evidence for stereoselective metabolism of only S-baclofen to an abundant oxidative deamination metabolite that is sterically resolved as the S-enantiomeric configuration. This metabolite undergoes some further metabolism by glucuronide conjugation. Consequences of this metabolic difference are a lower C_max and lower early plasma exposure of S-baclofen compared to R-baclofen and marginally lower urinary excretion of S-baclofen after racemic baclofen administration. These differences introduce compound-related exposure variances in humans in which subjects dosed with racemic baclofen are exposed to a prominent metabolite of baclofen whilst subjects dosed with STX209 are not. For potential clinical use, our findings suggest that STX209 has the advantage of being a biologically defined and active enantiomer.

Simulation of chemical metabolism for fate and hazard assessment. V. Mammalian hazard assessment

Animals and humans are exposed to a wide array of xenobiotics and have developed complex enzymatic mechanisms to detoxify these chemicals. Detoxification pathways involve a number of biotransformations, such as oxidation, reduction, hydrolysis and conjugation reactions. The intermediate substances created during the detoxification process can be extremely toxic compared with the original toxins, hence metabolism should be accounted for when hazard effects of chemicals are assessed. Alternatively, metabolic transformations could detoxify chemicals that are toxic as parents. The aim of the present paper is to describe specificity of eukaryotic metabolism and its simulation and incorporation in models for predicting skin sensitization, mutagenicity, chromosomal aberration, micronuclei formation and estrogen receptor binding affinity implemented in the TIMES software platform. The current progress in model refinement, data used to parameterize models, logic of simulating metabolism, applicability domain and interpretation of predictions are discussed. Examples illustrating the model predictions are also provided.

Constitutive expression and phenobarbital modulation of drug metabolizing enzymes and related nuclear receptors in cattle liver and extra-hepatic tissues

In humans and rodents, phenobarbital (PB) induces hepatic and extra-hepatic drug metabolizing enzymes (DMEs) through the activation of specific nuclear receptors (NRs). In contrast, few data about PB transcriptional effects in veterinary species are available. The constitutive expression and modulation of PB-responsive NR and DME genes, following an oral PB challenge, were investigated in cattle liver and extra-hepatic tissues (duodenum, kidney, lung, testis, adrenal and muscle). Likewise to humans and rodents, target genes were expressed to a lower extent compared to the liver with few exceptions. Phenobarbital significantly affected hepatic CYP2B22, 2C31, 2C87, 3A and UDP-glucuronosyltransferase 1A1-like, glutathione S-transferase A1-like and sulfotransferase 1A1-like (SULT1A1-like) mRNAs and apoprotein amounts; in extra-hepatic tissues, only duodenum showed a significant down-regulation of SULT1A1-like gene and apoprotein. Nuclear receptor mRNAs were never affected by PB. Presented data are the first evidence about the constitutive expression of foremost DME and NR genes in cattle extra-hepatic tissues, and the data obtained following a PB challenge are suggestive of species-differences in drug metabolism; altogether, these information are of value for the extrapolation of pharmacotoxicological data among species, the characterization of drug-drug interactions as well as the animal and consumer's risk caused by harmful residues formation.

Radiosynthesis and Radiotracer Properties of a 7-(2-[18F]Fluoroethoxy)-6-methoxypyrrolidinylquinazoline for Imaging of Phosphodiesterase 10A with PET

Phosphodiesterase 10A (PDE10A) is a key enzyme of intracellular signal transduction which is involved in the regulation of neurotransmission. The molecular imaging of PDE10A by PET is expected to allow a better understanding of physiological and pathological processes related to PDE10A expression and function in the brain. The aim of this study was to develop a new ¹⁸F-labeled PDE10A ligand based on a 6,7-dimethoxy-4-pyrrolidinylquinazoline and to evaluate its properties in biodistribution studies. Nucleophilic substitution of the 7-tosyloxy-analogue led to the 7-[¹⁸F]fluoroethoxy-derivative [¹⁸F]IV with radiochemical yields of 25% ± 9% (n = 9), high radiochemical purity of ≥99% and specific activities of 110–1,100 GBq/μmol. [¹⁸F]IV showed moderate PDE10A affinity (K_D,PDE10A = 14 nM) and high metabolic stability in the brain of female CD-1 mice, wherein the radioligand entered rapidly with a peak uptake of 2.3% ID/g in striatum at 5 min p.i. However, ex vivo autoradiographic and in vivo blocking studies revealed no target specific accumulation and demonstrated [¹⁸F]IV to be inapplicable for imaging PDE10A with PET.

Cytochrome P450s in the synthesis of cholesterol and bile acids--from mouse models to human diseases

The present review describes the transgenic mouse models that have been designed to evaluate the functions of the cytochrome P450s involved in cholesterol and bile acid synthesis, as well as their link with disease. The knockout of cholesterogenic Cyp51 is embrionally lethal, with symptoms of Antley-Bixler syndrome occurring in mice, whereas the evidence for this association is conflicting in humans. Disruption of Cyp7a1 from classic bile acid synthesis in mice leads to either increased postnatal death or a milder phenotype with elevated serum cholesterol. The latter is similar to the case in humans, where CYP7A1 mutations associate with high plasma low-density lipoprotein and hepatic cholesterol content, as well as deficient bile acid excretion. Disruption of Cyp8b1 from an alternative bile acid pathway results in the absence of cholic acid and a reduced absorption of dietary lipids; however, the human CYP8B1 polymorphism fails to explain differences in bile acid composition. Unexpectedly, apparently normal Cyp27a1(-/-) mice still synthesize bile acids that originate from the compensatory pathway. In humans, CYP27A1 mutations cause cerebrotendinous xanthomatosis, suggesting that only mice can compensate for the loss of alternative bile acid synthesis. In line with this, Cyp7b1 knockouts are also apparently normal, whereas human CYP7B1 mutations lead to a congenital bile acid synthesis defect in children or spastic paraplegia in adults. Mouse knockouts of the brain-specific Cyp46a1 have reduced brain cholesterol excretion, whereas, in humans, CYP46A1 polymorphisms associate with cognitive impairment. At present, cytochrome P450 family 39 is poorly characterized. Despite important physiological differences between humans and mice, mouse models prove to be an invaluable tool for understanding the multifactorial facets of cholesterol and bile acid-related disorders.

Distinct populations of hepatic stellate cells in the mouse liver have different capacities for retinoid and lipid storage

Hepatic stellate cell (HSC) lipid droplets are specialized organelles for the storage of retinoid, accounting for 50–60% of all retinoid present in the body. When HSCs activate, retinyl ester levels progressively decrease and the lipid droplets are lost. The objective of this study was to determine if the HSC population in a healthy, uninjured liver demonstrates heterogeneity in its capacity for retinoid and lipid storage in lipid droplets. To this end, we utilized two methods of HSC isolation, which leverage distinct properties of these cells, including their vitamin A content and collagen expression. HSCs were isolated either from wild type (WT) mice in the C57BL/6 genetic background by flotation in a Nycodenz density gradient, followed by fluorescence activated cell sorting (FACS) based on vitamin A autofluorescence, or from collagen-green fluorescent protein (GFP) mice by FACS based on GFP expression from a GFP transgene driven by the collagen I promoter. We show that GFP-HSCs have: (i) increased expression of typical markers of HSC activation; (ii) decreased retinyl ester levels, accompanied by reduced expression of the enzyme needed for hepatic retinyl ester synthesis (LRAT); (iii) decreased triglyceride levels; (iv) increased expression of genes associated with lipid catabolism; and (v) an increase in expression of the retinoid-catabolizing cytochrome, CYP2S1. Conclusion: Our observations suggest that the HSC population in a healthy, uninjured liver is heterogeneous. One subset of the total HSC population, which expresses early markers of HSC activation, may be “primed” and ready for rapid response to acute liver injury.

Animal products, diseases and drugs: a plea for better integration between agricultural sciences, human nutrition and human pharmacology

Eicosanoids are major players in the pathogenesis of several common diseases, with either overproduction or imbalance (e.g. between thromboxanes and prostacyclins) often leading to worsening of disease symptoms. Both the total rate of eicosanoid production and the balance between eicosanoids with opposite effects are strongly dependent on dietary factors, such as the daily intakes of various eicosanoid precursor fatty acids, and also on the intakes of several antioxidant nutrients including selenium and sulphur amino acids. Even though the underlying biochemical mechanisms have been thoroughly studied for more than 30 years, neither the agricultural sector nor medical practitioners have shown much interest in making practical use of the abundant high-quality research data now available. In this article, we discuss some specific examples of the interactions between diet and drugs in the pathogenesis and therapy of various common diseases. We also discuss, using common pain conditions and cancer as specific examples, how a better integration between agricultural science, nutrition and pharmacology could lead to improved treatment for important diseases (with improved overall therapeutic effect at the same time as negative side effects and therapy costs can be strongly reduced). It is shown how an unnaturally high omega-6/omega-3 fatty acid concentration ratio in meat, offal and eggs (because the omega-6/omega-3 ratio of the animal diet is unnaturally high) directly leads to exacerbation of pain conditions, cardiovascular disease and probably most cancers. It should be technologically easy and fairly inexpensive to produce poultry and pork meat with much more long-chain omega-3 fatty acids and less arachidonic acid than now, at the same time as they could also have a similar selenium concentration as is common in marine fish. The health economic benefits of such products for society as a whole must be expected vastly to outweigh the direct costs for the farming sector.

Constitutive expression of drug metabolizing enzymes and related transcription factors in cattle testis and their modulation by illicit steroids

In veterinary species, little information about extrahepatic drug metabolism is actually available. Therefore, the presence of foremost drug metabolizing enzymes (DMEs) and related transcription factors mRNAs was initially investigated in cattle testis; then, their possible modulation following the in vivo exposure to illicit growth promoters (GPs), which represent a major issue in cattle farming, was explored. All target genes were expressed in cattle testis, albeit to a lower extent compared to liver ones; furthermore, illicit protocols containing dexamethasone and 17β-oestradiol significantly up-regulated cytochrome P450 1A1, 2E1, oestrogen receptor-α and peroxisome proliferator-activated receptor-α mRNA levels. Overall, the constitutive expression of foremost DMEs and related transcription factors was demonstrated for the first time in cattle testis and illicit GPs were shown to affect pre-transcriptionally some of them, with possible consequences upon testicular xenobiotic drug metabolism.

Isolation and characterization of the CYP2D6 gene in Felidae with comparison to other mammals

The highly polymorphic CYP2D6 protein metabolizes about 25% of commonly used drugs and underlies a broad spectrum of drug responses among individuals. In contrast to extensive knowledge on the human CYP2D6 gene, little is known about the gene in non-human mammals. CYP2D6 mRNA from 23 cats (Felidae) spanning seven species were compared to available CYPD6 sequences in ten additional mammals and multiple allelic variants in humans. A relatively high mean dN/dS ratio (0.565) was observed, especially within Felidae. Pairwise dN/dS ratios were non-monotonically distributed with respect to evolutionary distance suggesting either positive selection or retention of slightly deleterious mutations. Positive selection on specific codons, most notably in regions involved in substrate recognition and membrane anchoring is supported and the possible influence of diet on specific amino acid changes in substrate binding sites is discussed.

Molecular characterization of the endoplasmic reticulum: insights from proteomic studies

The endoplasmic reticulum (ER) is a multifunctional intracellular organelle responsible for the synthesis, processing and trafficking of a wide variety of proteins essential for cell growth and survival. Therefore, comprehensive characterization of the ER proteome is of great importance to the understanding of its functions and has been actively pursued in the past decade by scientists in the proteomics field. This review summarizes major proteomic studies published in the past decade that focused on the ER proteome. We evaluate the data sets obtained from two different organs, liver and pancreas each of which contains a primary cell type (hepatocyte and acinar cell) with specialized functions. We also discuss how the nature of the proteins uncovered is related to the methods of organelle purification, organelle purity and the techniques used for protein separation prior to MS. In addition, this review also puts emphasis on the biological insights gained from these studies regarding the molecular functions of the ER including protein synthesis and translocation, protein folding and quality control, ER-associated degradation and ER stress, ER export and membrane trafficking, calcium homeostasis and detoxification and drug metabolism.

Nonviral gene transfer as a tool for studying transcription regulation of xenobiotic metabolizing enzymes

Numerous xenobiotic metabolizing enzymes are regulated by nuclear receptors at transcriptional level. The challenge we currently face is to understand how a given nuclear receptor interacts with its xenobiotics, migrates into nucleus, binds to the xenobiotic response element of a target gene, and regulates transcription. Toward this end, new methods have been developed to introduce the nuclear receptor gene into appropriate cells and study its activity in activating reporter gene expression under the control of a promoter containing xenobiotic response elements. The goal of this review is to critically examine the gene transfer methods currently available. We concentrate on the gene transfer mechanism, advantages and limitations of each method when employed for nuclear receptor-mediated gene regulation studies. It is our hope that the information provided highlights the importance of gene transfer in studying the mechanisms by which our body eliminates the potentially harmful substances and maintains the homeostasis.

The effect of standardized Echinacea purpurea extract on rat cytochrome P450 expression level

It is claimed that application of botanical supplements or herbal medicinal products with synthetic drugs that are cytochrome P450 enzymes substrates may induce significant herb-drug interactions and may alter pharmacotherapy. Echinacea preparations are one of the best selling products in the Europe and their medicinal use is still increasing but data about interactions of Echinacea extract with CYP enzymes are limited. In this study, we have investigated potential influence of standardized Echinacea purpurea extract containing 3.7% polyphenolic compounds on the mRNA expression level of major CYP450 enzymes using animal model. Total RNA was isolated from the rat liver tissue according to the manufacturer's protocol. Complementary DNA was synthesized from a mature mRNA template using reverse transcription. The level of mRNA expression in liver was analyzed by real-time quantitative PCR using specific target primers for CYP450 genes. In this study, it was demonstrated a significant increase of rat CYP2D1 and CYP1A1 expression level by 40% (p = 0.007) and 80% (p = 0.01), respectively. A weak inductory effect of the extract was observed for CYP1A2 by 16% (p > 0.05) compared with the control group. The levels of rat CYP3A1 and CYP3A2 mRNA were reduced by 41% (p < 0.05) and 25% (p = 0.001), respectively. A weak inhibitory effect was observed for CYP2D2 by 15% (p = 0.008) and CYP2C6 by 18% (p = 0.004) after long application of the Echinacea ethanolic extract. CYP2D2 and CYP2C6 activities were also inhibited by extract but in a lesser degree than CYP3A1 activity. Moreover, very little or no inhibition was noted for CYP2E1 both after 3 and 10 days of treatment. Our in vivo data indicate that the Echinacea ethanolic extract can potently inhibit the expression of CYP3A1/2 and can also induce of CYP1A1, CYP2D1. These findings suggest that Echinacea extract may influence the P450-mediated metabolism of different drugs and may initiate chemical carcinogenesis by activation of some compounds to their carcinogenic metabolites.

Overview of extracellular microvesicles in drug metabolism

IMPORTANCE OF THE FIELD

Liver is the major body reservoir for enzymes involved in the metabolism of endogenous and xenobiotic compounds. Recently, it has been shown that hepatocytes release exosome-like vesicles to the extracellular medium, and the proteomic characterization of these hepatocyte-secreted exosomes has revealed the presence of several of these enzymes on them.

AREAS COVERED IN THIS REVIEW

A systematic bibliographic search focused on two related aspects: i) xenobiotic-metabolizing enzymes that have been detected in microvesicles (MVs); and ii) MVs that are in the blood stream or secreted by cell types with clear interactions with this fluid.

WHAT THE READER WILL GAIN

A discussion of these hepatocyte-secreted vesicles along with other MVs as enzymatic carriers in the context of extrahepatic drug-metabolizing systems.

TAKE HOME MESSAGE

The contribution of many tissues including the liver to the MV plasma population is supported by several reports. On the other hand, many enzymes involved in the metabolism of drugs have been detected in MVs. Together, these observations support a role of hepatic-MVs in spreading the liver metabolizing activities through the body contributing in this manner to extrahepatic drug metabolism systems what could be relevant for body homeostasis and pharmaceutical interests.

Assessment of cytochrome P450 fluorometric substrates with rainbow trout and killifish exposed to dexamethasone, pregnenolone-16alpha-carbonitrile, rifampicin, and beta-naphthoflavone

Cytochrome P450s (CYPs) are important xenobiotic metabolizing proteins. While their functions are well understood in mammals, CYP function in non-mammalian vertebrate systems is much less defined, with function often inferred from mammalian data, assuming similar function across vertebrate species. In this study, we investigate whether in vivo treatment with known mammalian CYP inducers can alter the in vitro catalytic activity of fish microsomes using eleven fluorescent CYP-mediated substrates. We investigate the basal metabolism and induction potential for hepatic CYPs in two fish species, rainbow trout (Oncorhynchus mykiss) and killifish (Fundulus heteroclitus). Species differences were found in the baseline metabolism of these substrates. Killifish have significantly higher metabolic rates for all tested substrates except 7-benzyloxyquinoline and 7-benzyloxy-4-trifluoromethylcoumarin (both mammalian CYP3A substrates); significant differences were also seen between male and female killifish. Treatment with dexamethasone, pregnenolone-16alpha-carbonitrile, and rifampicin did not cause broad, measurable CYP induction in either fish species. In trout, dexamethasone (100 mg kg(-1)) significantly induced 3-cyano-7-ethoxycoumarin metabolism and rifampicin (100 mg kg(-1)) induced the dealkylation of 7-methoxyresorufin, although both were highly variable. Female killifish exposed to pregnenolone-16alpha-carbonitrile (100 mg kg(-1)) showed significantly higher metabolism of 7-pentoxyresorufin. Overall, dexamethasone, pregnenolone-16alpha-carbonitrile and rifampicin did not appear to consistently increase CYP activity in fish. Trout treated with 10 or 50 mg kg(-1) beta-naphthoflavone (BNF), a CYP1A inducer, showed significantly induced activity across almost all substrates tested, exceptions being 7-benzyloxyquinoline, 7-benzyloxy-4-trifluoromethylcoumarin and dibenzylfluorescein. 7-Methoxy-4-(aminomethyl)coumarin, a typical CYP2D substrate in mammals, was not metabolized by untreated fish liver microsomes; however, treatment with BNF significantly induced the metabolism of this substrate in trout. Induced substrate metabolism in BNF-treated microsomes was only correlated across selective substrates, suggesting that BNF induces multiple CYPs in fish liver. These include the known BNF inducible CYP1s plus a number of as yet unidentified fish CYPs. Overall, many of these catalytic assays could be valuable tools for identification of the function of specific CYP subfamilies and individual isoforms in fish.

Cytochrome P450-mediated metabolism in the human gut wall

Objective

Although the human small intestine serves primarily as an absorptive organ for nutrients and water, it also has the ability to metabolise drugs. Interest in the small intestine as a drug-metabolising organ has been increasing since the realisation that it is probably the most important extrahepatic site of drug biotransformation.

Key findings

Among the metabolising enzymes present in the small intestinal mucosa, the cytochromes P450 (CYPs) are of particular importance, being responsible for the majority of phase I drug metabolism reactions. Many drug interactions involving induction or inhibition of CYP enzymes, in particular CYP3A, have been proposed to occur substantially at the level of the intestine rather than exclusively within the liver, as originally thought. CYP3A and CYP2C represent the major intestinal CYPs, accounting for approximately 80% and 18%, respectively, of total immunoquantified CYPs. CYP2J2 is also consistently expressed in the human gut wall. In the case of CYP1A1, large interindividual variation in the expression levels has been reported. Data for the intestinal expression of the polymorphic CYP2D6 are conflicting. Several other CYPs, including the common hepatic isoform CYP2E1, are expressed in the human small intestine to only a very low extent, if at all. The distribution of most CYP enzymes is not uniform along the human gastrointestinal tract, being generally higher in the proximal regions of the small intestine.

Summary

This article reviews the current state of knowledge of CYP enzyme expression in human small intestine, the role of the gut wall in CYP-mediated metabolism, and how this metabolism limits the bioavailability of orally administered drugs. Possible interactions between drugs and CYP activity in the small intestine are also discussed.

Detection of EETs and HETE-generating cytochrome P-450 enzymes and the effects of their metabolites on myometrial and vascular function

Cytochrome P-450 (CYP450) enzymes of the CYP2 and -4 family in humans metabolize arachidonic acid to generate bioactive epoxyeicosatrienenoic acids (EETs) and hydroxyeicosatetrenoic acids (HETEs). We report significantly higher levels of CYP 2J2 protein expression following the onset of labor (n = 6, P < 0.05), implying increased EET-generating capacity within the uterus. Myometrial relaxation to 8,9-EET and 5,6-EET was observed, with the latter being inhibited by preincubation with 1 muM paxilline and is supported by whole cell recordings showing a modest effect of 5,6-EET on myometrial outward-current density (n = 4, P < 0.05). Only 5,6-EET of the EETs tested affected vascular reactivity (n = 6). Both 12- and 20-HETE (n = 5-6) caused vasoconstriction of partially depolarized blood vessels, with glibenclamide (n = 5) enhancing the effect of 12-HETE alone. Our findings signify a role for CYP2C9/19, -2J2, and -4A11/22 in late pregnancy, possibly related to the synthesis of lipid metabolites and downstream effects on vascular remodeling in the term pregnant uterus. The presence of CYP4A11/22 and their resultant procontractile metabolites could argue either a role in the control and initiation of labor and/or modification of the vascular delivery system to influence blood flow to the laboring uterus. The differential effects of the EETs and HETEs in the pregnant human uterus identify the CYP pathway as a novel modulator of myometrial and vascular physiology during late pregnancy.

Gene Expression Profiling in Rat Liver After VMH Lesioning

It has been reported that ventromedial hypothalamic (VMH) lesions induce hepatic cell proliferation and apoptosis and metabolic changes in the body. In the present study, we identified genes of which expression profiles showed significant modulation in rat liver after VMH lesions. Total RNA was extracted, and differences in the gene expression profiles between rats at day 3 after VMH lesioning and sham-VMH lesioned rats were investigated using DNA microarray analysis. The results revealed that VMH lesions regulated the genes that were involved in various types of metabolisms and cell proliferations in the liver. Real-time PCR also confirmed that gene expressions of ELOVL6 and SPC24 were upregulated, and that of SERPINA7 was downregulated. VMH lesions may change the expressions of multiple metabolism genes and cell proliferation–related genes in rat liver.

Dissimilar in vitro and in vivo effects of ellagic acid and its microbiota-derived metabolites, urolithins, on the cytochrome P450 1A1

This research shows that the dietary polyphenol ellagic acid (EA) and its colonic metabolites, urolithin-A (3,8-dihydroxy-6H-dibenzo[b,d]pyran-6-one, Uro-A) and urolithin-B (3-hydroxy-6H-dibenzo[b,d]pyran-6-one, Uro-B), modulate phase I and phase II detoxifying enzymes in colon cancer Caco-2 cells. EA and the urolithins, at micromolar concentrations achievable in the colon from the diet, induced the expression and activity of CYP1A1 and UGT1A10 and inhibited several sulfotransferases. As a result, the synthesis of glucuronides was favored over sulfated conjugates in the treated cells. In situ exposure to these compounds dissolved in buffer also led to the induction of CYP1A1 in the rat colon. However, in situ exposure to the compounds dissolved in oil or oral supplementation of the single compounds or pomegranate extract (PE) added to the feed failed to induce CYP1A1 in the colon mucosa. These results suggest that EA and urolithins may exert some blocking chemopreventive effects in the colon but that this effect is critically affected by interfering factors, such as the food matrix nature.

Cytochrome P450 oxidoreductase participates in nitric oxide consumption by rat brain

In low nanomolar concentrations, NO (nitric oxide) functions as a transmitter in brain and other tissues, whereas near-micromolar NO concentrations are associated with toxicity and cell death. Control of the NO concentration, therefore, is critical for proper brain function, but, although its synthesis pathway is well-characterized, the major route of breakdown of NO in brain is unclear. Previous observations indicate that brain cells actively consume NO at a high rate. The mechanism of this consumption was pursued in the present study. NO consumption by a preparation of central glial cells was abolished by cell lysis and recovered by addition of NADPH. NADPH-dependent consumption of NO localized to cell membranes and was inhibited by proteinase K, indicating the involvement of a membrane-bound protein. Purification of this activity yielded CYPOR (cytochrome P450 oxidoreductase). Antibodies against CYPOR inhibited NO consumption by brain membranes and the amount of CYPOR in several cell types correlated with their rate of NO consumption. NO was also consumed by purified CYPOR but this activity was found to depend on the presence of the vitamin E analogue Trolox (6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid), included in the buffer as a precaution against inadvertent NO consumption by lipid peroxidation. In contrast, NO consumption by brain membranes was independent of Trolox. Hence, it appears that, during the purification process, CYPOR becomes separated from a partner needed for NO consumption. Cytochrome P450 inhibitors inhibited NO consumption by brain membranes, making these proteins likely candidates.

Novel DNA sequence variations of cytochrome P450 genes in the Han Chinese population

Aim: Cytochrome P450 is an important monooxygenase responsible for the metabolism of a large variety of structurally diverse compounds. The aim of this study was to systematically investigate the DNA sequence variations in 14 cytochrome P450 genes relevant to drug metabolism in the Han Chinese population. Materials & methods: We sequenced these 14 genes in 23 subjects and determined the allele frequencies. Results: We identified a total of 312 genetic variants, which included 80 (25.6%) novel variants. These novel variants included 67 noncoding variants, four synonymous and nine nonsynonymous variants. Among these variants, an 11-nucleotide insertion in the 3´-flanking site of intron 6 in CYP2E1 (c.968-77_-76insGATGGGTGGAT) had the highest allele frequency of 0.565. A total of 16 of these novel variants were predicted to have potential functional consequences; however, among them only c.-1299T>A in CYP2C18 and c.-498C>A in CYP2D6 reached a frequency of 4.9%. Conclusions: This study establishes a genetic database of cytochrome P450 genes in the Han Chinese population and suggests further genetic diversity throughout this important gene family.

Brain drug-metabolizing cytochrome P450 enzymes are active in vivo, demonstrated by mechanism-based enzyme inhibition

Individuals vary in their response to centrally acting drugs, and this is not always predicted by drug plasma levels. Central metabolism by brain cytochromes P450 (CYPs) may contribute to interindividual variation in response to drugs. Brain CYPs have unique regional and cell-type expression and induction patterns, and they are regulated independently of their hepatic isoforms. In vitro, these enzymes can metabolize endogenous and xenobiotic substrates including centrally acting drugs, but there is no evidence to date of their in vivo function. This has been difficult to demonstrate in the presence of hepatically derived metabolites that may cross the blood-brain barrier. In addition, because of the membrane location of brain CYPs and the rate limiting effect of endogenous heme levels on the activity and appropriate membrane insertion of some induced CYPs, it has been unclear whether sufficient cofactors and coenzymes are present for constitutive and induced CYP forms to be enzymatically active. We have developed a method using a radiolabeled mechanism-based inhibitor of CYP2B1, (3)H-8-methoxypsoralen, to demonstrate for the first time that both the constitutive and induced forms of this enzyme are active in situ in the living rat brain. This methodology provides a novel approach to assess the function of enzymes in extrahepatic tissues, where expression levels are often low. Selective induction of metabolically active drug metabolizing enzymes in the brain may also provide ways to control prodrug activation in specific brain regions as a novel therapeutic avenue.

Molecular cloning of Bombyx mori cytochrome P450 gene and its involvement in fluoride resistance

To investigate the effects of fluorosis on development and gene expression profiles of silkworm, highly resistant silkworm strain 441, and highly susceptible silkworm strain 440 were treated with 200ppm fluoride (designated as 440F and 441F) and water (designated as 440DZ and 441DZ). Fluorotic silkworm showed body color and behavior changes. Statistical analysis indicated that growth index of 440F was lower than 440DZ, 441DZ, and 441F. The mortality of 440F was higher than others. Fluorescent differential display enabled us to obtain a differentially expressed cDNA. Bioinformatics analyses indicated that it belonged to cytochrome P450 family, denoted Bmcyp306a1, which contained seven exons and six introns. Phylogenetic tree showed BmCYP306A1 had high homology with Manduca sexta' P450 protein. Expression analysis indicated that Bmcyp306a1 was exclusively expressed in 441DZ and 441F and was down-regulated under fluoride treatment. The tissue-specific expression indicated Bmcyp306a1 had high-expression level in midgut and ovary in 441F. The data revealed that there was obvious dose-effect and times relationship with the pathological changes and gene expression. Expression profiles of Bmcyp306a1 suggested that P450 gene was crucial to physiological modification and might be involved in fluoride resistance.

Proteasome inhibition compromises direct retention of cytochrome P450 2C2 in the endoplasmic reticulum

To determine whether protein degradation plays a role in the endoplasmic reticulum (ER) retention of cytochromes P450, the effects of proteasomal inhibitors on the expression and distribution of green fluorescent protein chimeras of CYP2C2 and related proteins was examined. In transfected cells, expression levels of chimeras of full-length CYP2C2 and its cytosolic domain, but not its N-terminal transmembrane sequence, were increased by proteasomal inhibition. Redistribution of all three chimeras from the reticular ER into a perinuclear compartment and, in a subset of cells, also to the cell surface was observed after proteasomal inhibition. Redistribution was blocked by the microtubular inhibitor, nocodazole, suggesting that redistribution to the cell surface followed the conventional vesicular transport pathway. Similar redistributions were detected for BAP31, a CYP2C2 binding chaperone; CYP2E1 and CYP3A4, which are also degraded by the proteasomal pathway; and for cytochrome P450 reductase, which does not undergo proteasomal degradation; but not for the ER membrane proteins, sec61 and calnexin. Redistribution does not result from saturation of an ER retention "receptor" since in some cases protein levels were unaffected. Proteasomal inhibition may, therefore, alter ER retention by affecting a protein critical for ER retention, either directly, or indirectly by affecting the composition of the ER membranes.

Inhibition and induction of human cytochrome P450 enzymes: current status

Variability of drug metabolism, especially that of the most important phase I enzymes or cytochrome P450 (CYP) enzymes, is an important complicating factor in many areas of pharmacology and toxicology, in drug development, preclinical toxicity studies, clinical trials, drug therapy, environmental exposures and risk assessment. These frequently enormous consequences in mind, predictive and pre-emptying measures have been a top priority in both pharmacology and toxicology. This means the development of predictive in vitro approaches. The sound prediction is always based on the firm background of basic research on the phenomena of inhibition and induction and their underlying mechanisms; consequently the description of these aspects is the purpose of this review. We cover both inhibition and induction of CYP enzymes, always keeping in mind the basic mechanisms on which to build predictive and preventive in vitro approaches. Just because validation is an essential part of any in vitro-in vivo extrapolation scenario, we cover also necessary in vivo research and findings in order to provide a proper view to justify in vitro approaches and observations.

Influence of protein-protein interactions on the cellular localization of cytochrome P450

BACKGROUND

Microsomal CYPs are integral membrane proteins that are localized in the endoplasmic reticulum (ER), which is critical for their function. CYPs are co-translationally inserted into the rough ER membrane and are then either directly retained in the smooth ER or retained by a retrieval mechanism or targeted for ER-associated degradation. Protein-protein interactions are likely to be important for proper cellular targeting of CYPs.

OBJECTIVE

Progress in understanding the mechanisms of cellular targeting and ER retention of CYPs is reviewed with emphasis on the role of protein-protein interactions. Possible mechanisms of direct retention are the incorporation of CYPs into an immobile complex in the ER membrane, homooligomerization that prevents inclusion in transport vesicles, exclusion of CYP monomers from transport vesicles or targeting of CYPs to an ER subdomain away from sites of transport vesicle formation. Degradation of CYPs occurs either by lysosomal mechanisms or by the ubiquitin-proteasomal pathway.

METHODS

The scope of this review includes studies published in the research literature that have defined the targeting of CYPs to the ER, the retention of CYPs in the ER and the degradation of CYPs.

RESULTS/CONCLUSION

Targeting of CYPs to the ER is well understood and involves signal recognition particle-mediated delivery to the sec61 complex. The mechanism of ER retention of CYPs remains unclear, but self-oligomerization or binding to large immobile networks do not underlie ER retention of CYPs. An ER retention 'receptor' remains elusive, but BAP31 is important for the proper cellular localization of CYPs and Dap1p is a CYP-binding protein that is a candidate for such a receptor. Identification of protein binding partners of CYPs will be critical to understanding the mechanism of ER retention.

Topology of molecular machines of the endoplasmic reticulum: a compilation of proteomics and cytological data

The endoplasmic reticulum (ER) is a key organelle of the secretion pathway involved in the synthesis of both proteins and lipids destined for multiple sites within and without the cell. The ER functions to both co- and post-translationally modify newly synthesized proteins and lipids and sort them for housekeeping within the ER and for transport to their sites of function away from the ER. In addition, the ER is involved in the metabolism and degradation of specific xenobiotics and endogenous biosynthetic products. A variety of proteomics studies have been reported on different subcompartments of the ER providing an ER protein dictionary with new data being made available on many protein complexes of relevance to the biology of the ER including the ribosome, the translocon, coatomer proteins, cytoskeletal proteins, folding proteins, the antigen-processing machinery, signaling proteins and proteins involved in membrane traffic. This review examines proteomics and cytological data in support of the presence of specific molecular machines at specific sites or subcompartments of the ER.

Biomedical Technologies for in vitro Screening and Controlled Delivery of Neuroactive Compounds

Cell culture models can provide information pertaining to the effective dose, toxiciology, and kinetics, for a variety of neuroactive compounds. However, many in vitro models fail to adequately predict how such compounds will perform in a living organism. At the systems level, interactions between organs can dramatically affect the properties of a compound by alteration of its biological activity or by elimination of it from the body. At the tissue level, interaction between cell types can alter the transport properties of a particular compound, or can buffer its effects on target cells by uptake, processing, or changes in chemical signaling between cells. In any given tissue, cells exist in a three-dimensional environment bounded on all sides by other cells and components of the extracellular matrix, providing kinetics that are dramatically different from the kinetics in traditional two-dimensional cell culture systems. Cell culture analogs are currently being developed to better model the complex transport and processing that occur prior to drug uptake in the CNS, and to predict blood-brain barrier permeability. These approaches utilize microfluidics, hydrogel matrices, and a variety of cell types (including lung epithelial cells, hepatocytes, adipocytes, glial cells, and neurons) to more accurately model drug transport and biological activity. Similar strategies are also being used to control both the spatial and temporal release of therapeutic compounds for targeted treatment of CNS disease.