Cortical Proteins Associated With Cognitive Resilience in Community-Dwelling Older Persons

Importance

Identifying genes and proteins for cognitive resilience (ie, targets that may be associated with slowing or preventing cognitive decline regardless of the presence, number, or combination of common neuropathologic conditions) provides a complementary approach to developing novel therapeutics for the treatment and prevention of Alzheimer disease and related dementias.

Objective

To identify proteins associated with cognitive resilience via a proteome-wide association study of the human dorsolateral prefrontal cortex.

Design, Setting, and Participants

This study used data from 391 community-dwelling older persons who participated in the Religious Orders Study and the Rush Memory and Aging Project. The Religious Orders Study began enrollment January 1, 1994, and the Rush Memory and Aging Project began enrollment September 1, 1997, and data were collected and analyzed through October 23, 2019.

Exposures

Participants had undergone annual detailed clinical examinations, postmortem evaluations, and tandem mass tag proteomics analyses.

Main Outcomes and Measures

The outcome of cognitive resilience was defined as a longitudinal change in cognition over time after controlling for common age-related neuropathologic indices, including Alzheimer disease, Lewy bodies, transactive response DNA-binding protein 43, hippocampal sclerosis, infarcts, and vessel diseases. More than 8000 high abundance proteins were quantified from frozen dorsolateral prefrontal cortex tissue using tandem mass tag and liquid chromatography-mass spectrometry.

Results

There were 391 participants (273 women); their mean (SD) age was 79.7 (6.7) years at baseline and 89.2 (6.5) years at death. Eight cortical proteins were identified in association with cognitive resilience: a higher level of NRN1 (estimate, 0.140; SE, 0.024; P = 7.35 × 10-9), ACTN4 (estimate, 0.321; SE, 0.065; P = 9.94 × 10-7), EPHX4 (estimate, 0.198; SE, 0.042; P = 2.13 × 10-6), RPH3A (estimate, 0.148; SE, 0.031; P = 2.58 × 10-6), SGTB (estimate, 0.211; SE, 0.045; P = 3.28 × 10-6), CPLX1 (estimate, 0.136; SE, 0.029; P = 4.06 × 10-6), and SH3GL1 (estimate, 0.179; SE, 0.039; P = 4.21 × 10-6) and a lower level of UBA1 (estimate, -0.366; SE, 0.076; P = 1.43 × 10-6) were associated with greater resilience.

Conclusions and Relevance

These protein signals may represent novel targets for the maintenance of cognition in old age.

Development of Improved Double-Nanobody Sandwich ELISAs for Human Soluble Epoxide Hydrolase Detection in Peripheral Blood Mononuclear Cells of Diabetic Patients and the Prefrontal Cortex of Multiple Sclerosis Patients

Nanobodies have been progressively replacing traditional antibodies in various immunological methods. However, the use of nanobodies as capture antibodies is greatly hampered by their poor performance after passive adsorption to polystyrene microplates, and this restricts the full use of double nanobodies in sandwich enzyme-linked immunosorbent assays (ELISAs). Herein, using the human soluble epoxide hydrolase (sEH) as a model analyte, we found that both the immobilization format and the blocking agent have a significant influence on the performance of capture nanobodies immobilized on polystyrene and the subsequent development of double-nanobody sandwich ELISAs. We first conducted epitope mapping for pairing nanobodies and then prepared a horseradish-peroxidase-labeled nanobody using a mild conjugation procedure as a detection antibody throughout the work. The resulting sandwich ELISA using a capture nanobody (A9, 1.25 μg/mL) after passive adsorption and bovine serum albumin (BSA) as a blocking agent generated a moderate sensitivity of 0.0164 OD·mL/ng and a limit of detection (LOD) of 0.74 ng/mL. However, the introduction of streptavidin as a linker to the capture nanobody at the same working concentration demonstrated a dramatic 16-fold increase in sensitivity (0.262 OD·mL/ng) and a 25-fold decrease in the LOD for sEH (0.03 ng/mL). The streptavidin-bridged double-nanobody ELISA was then successfully applied to tests for recovery, cross-reactivity, and real samples. Meanwhile, we accidentally found that blocking with skim milk could severely damage the performance of the capture nanobody by an order of magnitude compared with BSA. This work provides guidelines to retain the high effectiveness of the capture nanobody and thus to further develop the double-nanobody ELISA for various analytes.

Maternal Smoking during Early Pregnancy, GSTP1 and EPHX1 Variants, and Risk of Isolated Orofacial Clefts

Objective:

To examine the interactions between four fetal xenobiotic metabolizing gene polymorphisms, maternal cigarette smoking, and risk for oral cleft defects.

Design and Participants:

California population–based case-control study of 431 infants born with isolated orofacial clefts and 299 nonmalformed controls.

Main Outcome Measures:

Infants were genotyped for functional polymorphisms of the detoxification enzymes microsomal epoxide hydrolase-1 (EPHX1 T→C [Tyr113His], and A→G [His139Arg]), and glutathione-S transferase Pi-1 (GSTP1 A→G [Ile105Val] and C→T [Ala114Val]), and risks for cleft outcomes were measured for gene only and gene-maternal smoking effects.

Results:

Although smoking was associated with an increased risk for isolated cleft lip ± palate, we found no independent associations of genotypes of EPHX1-codon 113 or GSTP1-codon 105 polymorphisms for either isolated cleft lip ± palate or isolated cleft palate. The heterozygote genotype for the EPHX1-codon 139 polymorphism was associated with an increased risk of isolated cleft palate (odds ratio = 1.6 [95% confidence interval, 1.0 to 2.6]). Infant EPHX1 and GTSP1 polymorphic variants did not appreciably alter the risks for clefts associated with maternal smoking, nor were any EPHX1 combined genotype-specific risks found. Infant genotypes of the GSTP1-codon 105 polymorphism, combined with glutathione-S-transferase-μ-1 null genotypes, did not appreciably alter the risk of orofacial clefts.

Conclusions:

Our results suggest that genetic variation of the detoxification enzymes EPHX1 and GSTP1 did not increase the risks of orofacial clefting, nor do they influence the risks associated with maternal smoking.

Arabidopsis thaliana EPOXIDE HYDROLASE1 (AtEH1) is a cytosolic epoxide hydrolase involved in the synthesis of poly-hydroxylated cutin monomers

Epoxide hydrolases (EHs) are present in all living organisms. They have been extensively characterized in mammals; however, their biological functions in plants have not been demonstrated. Based on in silico analysis, we identified AtEH1 (At3g05600), a putative Arabidopsis thaliana epoxide hydrolase possibly involved in cutin monomer synthesis. We expressed AtEH1 in yeast and studied its localization in vivo. We also analyzed the composition of cutin from A. thaliana lines in which this gene was knocked out. Incubation of recombinant AtEH1 with epoxy fatty acids confirmed its capacity to hydrolyze epoxides of C18 fatty acids into vicinal diols. Transfection of Nicotiana benthamiana leaves with constructs expressing AtEH1 fused to enhanced green fluorescent protein (EGFP) indicated that AtEH1 is localized in the cytosol. Analysis of cutin monomers in loss-of-function Ateh1-1 and Ateh1-2 mutants showed an accumulation of 18-hydroxy-9,10-epoxyoctadecenoic acid and a concomitant decrease in corresponding vicinal diols in leaf and seed cutin. Compared with wild-type seeds, Ateh1 seeds showed delayed germination under osmotic stress conditions and increased seed coat permeability to tetrazolium red. This work reports a physiological role for a plant EH and identifies AtEH1 as a new member of the complex machinery involved in cutin synthesis.

Heavy chain single-domain antibodies to detect native human soluble epoxide hydrolase

The soluble epoxide hydrolase (sEH) is a potential pharmacological target for treating hypertension, vascular inflammation, pain, cancer, and other diseases. However, there is not a simple, inexpensive, and reliable method to estimate levels of active sEH in tissues. Toward developing such an assay, a polyclonal variable domain of heavy chain antibody (VHH) sandwich immunoassay was developed. Ten VHHs, which are highly selective for native human sEH, were isolated from a phage-displayed library. The ten VHHs have no significant cross-reactivity with human microsomal epoxide hydrolase, rat and mouse sEH, and denatured human sEH. There is a high correlation between protein levels of the sEH determined by the enzyme-linked immunosorbent assay (ELISA) and the catalytic activity of the enzyme in S9 fractions of human tissues (liver, kidney, and lung). The VHH-based ELISA appears to be a new reliable method for monitoring the sEH and may be useful as a diagnostic tool for diseases influenced by sEH. This study also demonstrates the broad utility of VHH in biochemical and pharmacological research.

Soluble epoxide hydrolase inhibitory and anti-inflammatory components from the leaves of Eucommia ulmoides Oliver (duzhong)

Eucommia ulmoides leaves have been used as a functional food and drink in China. The purpose of this study was to identify the bioactive constituents with soluble epoxide hydrolase (sEH) inhibitory activity and anti-inflammatory properties. Twenty-seven known compounds (1-27) were isolated from the leaves of E. ulmoides Oliver, and their structures were identified by NMR and ESIMS analysis; three of these, 2,5-dimethoxy-3-glucopyranosyl cinnamic alcohol (11), foliasalacioside E2 (26), and icariside F2 (27), were obtained from this plant for the first time. Compounds 1-7 exhibited soluble epoxide hydrolase (sEH) inhibitory activity at 100 μM; among them, quercetin (1) and kaempferol (5) displayed potential activities with IC50 values of 22.5 ± 0.9 and 31.3 ± 2.6 μM, respectively, with noncompetitive inhibition mode. Nuclear factor kappa B (NF-κB) inhibitory activity of the isolated compounds was evaluated by the NF-κB liciferase assay in HepG2 cells. Compounds 1, 9, 20, and 27 displayed potent NF-κB inhibitory effects, with IC50 values of 15.14 ± 2.29, 15.23 ± 2.34, 16.88 ± 2.17, and 16.25 ± 2.19 μM, respectively, whereas other compounds showed weak inhibition of NF-κB transcriptional activity ranging from 17.54 to 92.6 μM. A structure-activity relationship of flavonoids 1-9 was also discussed. The results obtained in this work might contribute to the understanding of pharmacological activities of E. ulmoides leaves and further investigation on its potential application values for food and drug.

Protection of salvianolic acid A on rat brain from ischemic damage via soluble epoxide hydrolase inhibition

Epoxyeicosatrienoic acids (EETs) and their regulating enzyme soluble epoxide hydrolase (sEH) have been associated with ischemic stroke. Salvianolic acid A (SAA) is proved to display potent cerebroprotection. However, little information is available about the link between them. This study aimed to investigate whether SAA exhibits its protective effects in rats subjected to middle cerebral artery occlusion (MCAO) through sEH and EETs. The results showed that SAA treatment ameliorated neurological deficits and reduced infarct volume. Notably, the beneficial effects of SAA were attenuated by co-administration of (14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE)), a putative selective EETs antagonist. Furthermore, SAA increased the 14,15-EET levels in the blood and brain of sham and MCAO rats. Assay for hydrolase activity showed that 1 and 3 mg/kg of SAA significantly diminished brain sEH activity of MCAO rats. A fluorescent assay in vitro indicated that SAA could inhibit recombinant human sEH activity in a concentration-dependent manner (IC(50) = 1.62 μmol/l). Immunohistochemical analysis showed that SAA at the doses of 1 and 3 mg/kg significantly decreased sEH protein expression in hippocampus CA1 region of MCAO rats. In conclusion, cerebral protection of SAA is mediated, at least in part, via inhibiting sEH to increase EETs levels.

Dynamic expression of epoxyeicosatrienoic acid synthesizing and metabolizing enzymes in the primate corpus luteum

Epoxyeicosatrienoic acids (EpETrEs), produced from arachidonic acid via cytochrome P450 (CYP) epoxygenases, regulate inflammation, angiogenesis, cellular proliferation, ion transport and steroidogenesis. EpETrE actions are regulated through their metabolism to diols (dihydroxyeicosatrienoic acids; DiHETrE) via the enzyme soluble epoxide hydrolase (EPHX2). We set out to determine, therefore, whether EpETrE generating (epoxygenases CYP2C8, 2C9, 2C19, 2J2, 1A2 and 3A4) and metabolizing (EPHX2) enzymes are expressed in the primate corpus luteum (CL). CL were isolated from rhesus macaques during the early (day 3-5 post-LH surge), mid (day 6-8), mid-late (day 10-12), late (day 14-16) and very-late (day 17-19: menses) luteal phase of natural menstrual cycles. EPHX2 mRNA levels peaked in mid-late CL (5-fold when compared with early CL, P<0.05) and remained elevated in the late CL. Ablation of pituitary LH secretion and luteal steroid synthesis significantly reduced (P<0.05) EPHX2 mRNA levels in the mid-late CL, with progestin replacement being insufficient to restore its level of expression to control values. EPHX2 protein was localized to large and small luteal cells, as well as vascular endothelial cells. The EpETrE-generating CYP epoxygenase 2J2, 2C9 and 3A4 genes were also expressed in the macaque CL. While CYP2J2 mRNA levels did not significantly change through the luteal phase, CYP2C9 and CYP3A4 levels were significantly (P<0.05) higher in the mid-late phase when compared with the early phase. CYP2C9, 2J2 and 3A4 proteins were each localized to the large luteal cells, with 2C9 and 2J2 also being present in the small luteal, stromal and endothelial cells. These studies demonstrate for the first time that an EpETrE generating and metabolizing system exists in the primate CL, with the latter being regulated by LH and steroid hormone(s).

Assay for rapid analysis of the tri-peptidase activity of LTA4 hydrolase

Leukotriene A4 hydrolase is a bifunctional zinc metalloenzyme with an epoxide hydrolase activity as well as an arginyl tri-peptidase activity. Detailed enzymological and mechanistic investigations of the latter activity have been hampered by the lack of a rapid and convenient enzyme assay. Here we have developed a new method allowing direct spectrophotometric assessment of the tri-peptide cleaving activity of leukotriene A4 hydrolase, as well as other peptidases. The method utilizes two competing substrates, one chromogenic reference substrate together with the tri-peptide substrate of interest, and relies on computer-assisted analysis of progress curves. The chromogenic reference substrate serves to disclose the "invisible" tri-peptide substrate for kinetic analysis. The method is fast and simple and will allow detailed kinetic studies and screening for natural peptide substrates of leukotriene A4 hydrolase as well as other members of the M1 family of aminopeptidases.

Eicosanoid imbalance in the NOD mouse is related to a dysregulation in soluble epoxide hydrolase and 15-PGDH expression

Eicosanoids promote or resolve inflammation depending on the class produced. Macrophage from nonobese diabetic (NOD) mouse produce increased proinflammatory lipid mediators and low levels of antiinflammatory lipoxin A4 (LXA4). The enhanced proinflammatory eicosanoids is secondary to increased cyclooxygenase-2 (Cox-2) expression and low levels of prostaglandin/leukotriene catabolic enzyme, 15-hydroxyprostaglandin dehydrogenase (15-PGDH). Deficient LXA4 production is not due to deficient lipoxygenase (LO) activity, but is related to increased soluble epoxide hydrolase (sEH), involved in metabolism of anti-inflammatory epoxyeicosatrienoic acids (EET). These aberrations in eicosanoid biology suggest that inflammation in the NOD mouse is likely to be prolonged and robust and may contribute to type 1 diabetes (T1D) pathogenesis.

Distribution of soluble epoxide hydrolase, cytochrome P450 2C8, 2C9 and 2J2 in human malignant neoplasms

Soluble epoxide hydrolase (sEH) is a bifunctional enzyme with a C-terminal epoxide hydrolase activity and an N-terminal phosphatase activity. Arachidonic acid epoxides, previously suggested to be involved in apoptosis, oncogenesis and cell proliferation, are generated by cytochrome P450 epoxygenases and are good substrates of the sEH C-terminal domain. In addition, the N-terminal phosphatase domain hydrolyzes isoprenoid mono- and pyrophosphates, which are involved in cell signaling and apoptosis. Here we provide a comprehensive analysis of the distribution of sEH, CYP2C8, 2C9 and 2J2 in human neoplastic tissues using tissue micro-arrays. The human neoplastic tissue micro-arrays provide a well-controlled side by side analysis of a wide array of neoplastic tissues and their surrounding normal tissue controls. Many of the neoplastic tissues showed altered expression of these enzymes as compared to normal tissues. Altered expression was not limited to the neoplastic tissues but also found in the surrounding non-neoplastic tissues. For example, sEH expression in renal and hepatic malignant neoplasms and surrounding non-neoplastic tissues was found to be significantly decreased, whereas expression was found to be increased in seminoma as compared to normal tissues. Our study warrants further investigation of the role of altered expression of these enzymes in neoplastic tissues.

Colorimetric assays for quantitative analysis and screening of epoxide hydrolase activity

Focusing on directed evolution to tailor enzymes as usable biocatalysts for fine chemistry, we have studied in detail several colorimetric assays for quantitative analysis of epoxide hydrolase (EH) activity. In particular, two assays have been optimized to characterize variants issued from the directed evolution of the EH from Aspergillus niger. Assays described in this paper are sufficiently reliable for quantitative screening of EH activity in microtiter plates and are low cost alternatives to GC or MS analysis. Moreover, they are usable for various epoxides and not restricted to a type of substrate, such as those amenable to assay by UV absorbancy. They can be used to assay EH activity on any epoxide and to directly assay enantioselectivity when both (R) and (S) substrates are available. The advantages and drawbacks of these two methods to assay EH activity of a large number of natural samples are summarized.

Identification and characterisation of soluble epoxide hydrolase in mouse brain by a robust protein biochemical method

The central nervous system is an important potential target for certain environmental prototoxins, but relatively little is known regarding brain-specific expression of biotransformation enzyme systems. On the other hand, developments in the field of molecular biology and advances in high-throughput screening methods continue to increase the number and amounts of available proteins. We used thus a robust and reliable technique, two-dimensional gel electrophoresis coupled to matrix assisted laser desorption/ionisation mass spectroscopy followed by tandem mass spectrometry and identified for the first time soluble epoxide hydrolase and added other biotransformation enzymes in the hippocampal region of mouse brain. Soluble epoxide hydrolase has an Mr of 61.5 kDa, pI of 5.9, twenty-six matching peptides and sequence coverage of 56% and was unambiguously identified by MS/MS. Since localised biotransformation events in regions of the central nervous system may account for pathologies and/or toxicities initiated by exposure to certain endogenous and/or environmental chemicals, identification of these enzymes would present an opportunity for developing novel therapeutic targets or would have critical toxicologic significance.

Biocatalytic resolution of glycidyl aryl ethers by Trichosporon loubierii: cell/substrate ratio influences the optical purity of (R)-epoxides

Glycidyl aryl ethers were resolved by using lyophilized cells of Trichosporon loubierii ECU1040 having epoxide hydrolase activity. The activity and enantioselectivity depended on the structure of the aryl group. Different cell/substrate ratios also influenced the optical purity of remaining substrate. An additional stability test of the whole-cell enzyme suggests that rapid deactivation of the epoxide hydrolase was the potential reason. (R)-Epoxides were prepared in gram amounts with optical purity of 87% - 99% ee.

Leukotriene A4 hydrolase as a target for cancer prevention and therapy

Leukotriene A4 hydrolase (LTA4H) is a bifunctional zinc enzyme with the activities of epoxide hydrolase and aminopeptidase. As an epoxide hydrolase, LTA4H catalyzes the hydrolysis of the epoxide LTA4 to the diol, leukotriene B4 (LTB4), which mainly functions as a chemoattractant and an activator of inflammatory cells. As an aminopeptidase, LTA4H may process peptides related to inflammation and host defense. In a chronic inflammation-associated animal model of esophageal adenocarcinoma, we have shown that LTA4H was overexpressed in tumor as compared to normal tissues. Bestatin, an LTA4H inhibitor, suppresses tumorigenesis in this animal model. Since LTA4H has long been regarded as an anti-inflammatory target, we propose LTA4H as a target for prevention and therapy of cancers, especially those associated with chronic inflammation. Here we review the gene structure, expression, regulation and functions of LTA4H, as well as its involvement in carcinogenesis. We believe LTA4H/LTB4 may play an important role in chronic inflammation associated carcinogenesis by at least two mechanisms: a) the inflammation-augmenting effect on inflammatory cells through positive feedback mediated by its receptors and downstream signaling molecules; and b) the autocrine growth-stimulatory effect of LTB4 produced by epithelial cells, and the paracrine growth-stimulatory effect of LTB4 produced by inflammatory cells, on precancerous and cancer cells. Based on our present knowledge, inhibitors of LTA4H or antagonists of LTB4 receptors may be used alone or in combination with other agents (e.g., cyclooxygenase 2 inhibitors) in cancer prevention and treatment trials to test their effectiveness.

Fluorometric assay for determining epoxide hydrolase activity

We have developed a rapid screening procedure that enables the screening of hundreds of enzyme samples or variants for epoxide hydrolase activity towards any substrate. The procedure detects the products of the enzymatic reaction via periodate cleavage and remaining fluorescence of carboxyfluorescein.

Epoxide Hydrolases in the Rat Epididymis: Possible Roles in Xenobiotic and Endogenous Fatty Acid Metabolism

Epoxide hydrolases play an important role in detoxifying epoxides that arise from the metabolism of xenobiotic and endogenous compounds. Both the soluble and microsomal forms of epoxide hydrolase (sEH and mEH, respectively) have been detected in the rat testis. Because of the important role the epididymis plays in sperm maturation and protection, the present study evaluated the presence and activity of these two epoxide hydrolases in the rat epididymis. Using Western blotting, protein bands consistent in size with both mEH and sEH were detected in the caput, corpus, and cauda of the epididymis. The mEH immunoreactive bands in the epididymis ( approximately 50 kDa) were consistent with mEH detected in the liver and kidney. The sEH immunoreactive bands in the epididymis ( approximately 65 kDa) were consistent with a recombinant sEH standard and sEH detected in the liver, kidney, and testis. The presence of mEH and sEH in the epididymis was supported by observations from substrate-based enzyme assays. Results indicated that epididymal mEH can hydrolyze [(3)H]-cis-stilbene oxide to the corresponding diol at levels approximately 9% of the kidney. Epididymal sEH hydrolyzed the substrate [(3)H]-trans-diphenylpropene oxide to the corresponding diol and this activity was inhibited by cyclohexyl-dodecyl urea. Arachidonic acid epoxygenase activity was detected in epididymal S9 fractions, suggesting that fatty acid metabolism by epididymal cytochrome P450s can form epoxides that subsequently become substrates for epididymal sEH. Results from the present study indicate that the epididymis contains at least two active forms of epoxide hydrolase. The role of these enzymes in the detoxification of xenobiotic epoxides is well known, although it is unclear what cellular role they may play in the formation of biologically active metabolites in the epididymis.

Inhibition of human m-epoxide hydrolase gene expression in a case of hypercholanemia

Microsomal epoxide hydrolase (mEH) is a bifunctional protein that plays a central role in carcinogen metabolism and is also able to mediate the sodium-dependent uptake of bile acids into hepatocytes. Studies have identified a subject (S-1) with extremely elevated serum bile salt levels in the absence of observable hepatocellular injury, suggesting a defect in bile acid uptake. In this individual, mEH protein and mEH mRNA levels were reduced by approximately 95% and 85%, respectively, whereas the expression and amino acid sequence of another bile acid transport protein (NTCP) was unaffected. Sequence analysis of the mEH gene (EPHX1) revealed a point mutation at an upstream HNF-3 site (allele I) and in intron 1 (allele II), which resulted in a significant decrease in EPHX1 promoter activity in transient transfection assays. Gel shift assays using a radiolabeled oligonucleotide from each region resulted in specific transcription factor binding patterns, which were altered in the presence of the mutation. These studies demonstrate that the expression of mEH is greatly reduced in a patient with hypercholanemia, suggesting that mEH participates in sodium-dependent bile acid uptake in human liver where its absence may contribute to the etiology of this disease.

In vitro metabolism of the mammalian soluble epoxide hydrolase inhibitor, 1-cyclohexyl-3-dodecyl-urea

The metabolism of the soluble epoxide hydrolase (sEH) inhibitor, 1-cyclohexyl-3-dodecyl-urea (CDU), was studied in rat and human hepatic microsomes. The microsomal metabolism of CDU enhanced sEH inhibition potency of the reaction mixture and resulted in the formation of several metabolites. During the course of this study, a sensitive and specific high-performance liquid chromatography with tandem mass spectrometry analytical method was developed to investigate simultaneously the production of these metabolites. In both rat and human hepatic microsomes, CDU was ultimately transformed into the corresponding omega-carboxylate; however, the rodent tissue appeared to perform this transformation more rapidly. After a 60-min incubation in rat hepatic microsomes, the percentage of residual CDU, the omega-carboxylate, and the intermediary omega-hydroxyl were about 20%, 20%, and 50%, respectively. Carbon monoxide inhibited the metabolism of CDU by rat hepatic microsomes, suggesting that the initial step is catalyzed by cytochrome P450. Further metabolism was enhanced by the addition of NAD, suggesting that dehydrogenases are associated with intermediate metabolic steps. Regardless, the ultimate product of microsomal metabolism, 12-(3-cyclohexyl-ureido)-dodecanoic acid, is also an excellent sEH inhibitor with several hundred-fold higher solubility, supporting the hypothesis that CDU has prodrug characteristics. These findings will facilitate the rational design and optimization of sEH inhibitors with better physical properties and improved metabolic stability.

Effects of Green Tea and High-Fat Diet on Arachidonic Acid Metabolism and Aberrant Crypt Foci Formation in an Azoxymethane-Induced Colon Carcinogenesis Mouse Model

Excessive fat consumption is a risk factor for colon carcinogenesis, and green tea consumption may reduce the risk of colon and other cancers. The current study was designed to investigate the effects of green tea and a high-fat diet on arachidonic acid metabolism and aberrant crypt foci formation in an azoxymethane (AOM)-induced colon carcinogenesis mouse model. We also determined whether green tea consumption altered the size of regional fat pads. CF-1 female mice were maintained on either a high-fat (20% corn oil) or a low-fat (5% corn oil) diet. AOM was given subcutaneous at a dose of 7.5 mg/kg body weight at 6 wk and then a dose of 10 mg/kg at 7 wk of age. Two weeks after the second AOM injection, 0.6% green tea (6 mg tea solids/ml) was given as the drinking fluid and continued for 10 wk until the experiment was terminated. In the AOM-treated mice not receiving green tea, the high-fat diet significantly enhanced colonic levels of 5-lipoxygenase, leukotriene A4 hydrolase, and leukotriene B4, but it did not significantly alter prostaglandin E2 levels and aberrant crypt foci formation. In AOM-treated mice on the high-fat diet, green tea significantly decreased colonic levels of cytosolic phospholipase A2, 5-lipoxygenase, and leukotriene B4; green tea treatment also decreased the number of aberrant crypt foci (P < 0.05). The weights of parametrial and retroperitoneal fat pads were increased by the high-fat diet and decreased by green tea treatment. The current results indicate that green tea consumption and dietary fat modulate 5-lipoxygenase-dependent pathway of arachidonic acid metabolism during AOM-induced colon carcinogenesis. Green tea inhibits ACF formation in mice on a high corn oil diet, suggesting its possible inhibitory effect on colon carcinogenesis in populations such as those in Western countries that consume high amounts of fat.

A spectrophotometric assay for measuring and detecting an epoxide hydrolase activity

In this paper we report the development of a novel and simple spectrophotometric assay which allows one to achieve the continuous, rapid, sensitive, and accurate determination of an epoxide hydrolase activity. This assay is based on the elaboration of a coupled enzymatic/chemical methodology which allows quantification of the enzymatic activity within 3min, and offers good sensitivity of about 10 micro Mmin(-1). Applicability of this test to some other aromatic epoxides has been shown and some limitations have also been explored. This assay should be particularly useful for different applications, for example (a) activity localization during purification of such enzymes, (b) very rapid determination of kinetic constants, and (c) high-throughput screening experiments.

Identification of two tamoxifen target proteins by photolabeling with 4-(2-morpholinoethoxy)benzophenone

Our quest to identify target proteins involved in the activity of tamoxifen led to the design of photoaffinity ligand analogues of tamoxifen able to cross-link such proteins. A new tritiated photoprobe, 4-(2-morpholinoethoxy)benzophenone (MBoPE), was synthesized and used to identify proteins involved in tamoxifen binding in rat liver. MBoPE, which has structural features in common with the potential antagonist of the intracellular histamine receptor (N,N-diethyl-2-[(4-phenylmethyl)phenoxy]ethanamine HCl: DPPE) is unable to bind the estrogen receptor although it does compete with tamoxifen for an antiestrogen binding site (AEBS). This tritiated benzophenone derivative was obtained by metal-catalyzed halogen-tritium replacement reaction. Because of its high specific activity, four target proteins could be photolabeled, three of which were identified with M(r) of 60,000, 49,500, and 14,000, while the fourth at 27,500 was in too low an amount and could not be sequenced. The 49.5 kDa protein corresponded by mass spectrometry to the microsomal epoxide hydrolase already identified with an aryl azide photoprobe [Mesange, F., et al. (1998) Biochem. J. 334, 107-112]. The 60 and 14 kDa proteins were identified as the carboxylesterase (ES10) and the liver fatty acid binding protein (L-FABP), respectively. The inhibitory effect of tamoxifen on carboxylesterase activity and the competitive efficacy of oleic acid on [(3)H]tamoxifen binding suggest that both proteins are AEBS subunits. Moreover, treatment of hepatocytes with antisense mRNA directed against ES10 or L-FABP abolished both tamoxifen and MBoPE binding. On the basis of previous pharmacological arguments, the 27.5 kDa protein might correspond to the sigma I receptor. Altogether, these results confirm that the microsomal epoxide hydrolase is a target for tamoxifen and provide evidence of two new target proteins implicated in cell lipid metabolism.

Identification of the putative brain tumor antigen BF7/GE2 as the (de)toxifying enzyme microsomal epoxide hydrolase

Malignant gliomas are the main cause of death from primary brain tumors. Despite surgery, radiation, and chemotherapy, patients have a median survival of less than a few years; therefore, it is clearly imperative to investigate new ways of treatment. The development of new therapeutic strategies for brain tumors is dependent on a better understanding of the differences between normal and tumoral brain cells. Our group had described previously a Mr 48,000 antigen defined by reactivity with two monoclonal antibodies (GE2 and BF7) obtained by immunization of mice with human glioblastoma cells. Here, we describe the identification of the GE2/BF7 antigen as microsomal epoxide hydrolase (mEH), a drug-metabolizing enzyme that is involved both in toxification and detoxification of carcinogens. We initially used immunoaffinity purification using GE2 and BF7 and analyzed the purified proteins by microsequencing. Edman degradation identified 15 amino acids of the NH2-terminal sequence that were 100% identical to mEH. To further confirm the identity of the BF7/GE2 antigen as mEH, we showed that the protein immunopurified with GE2 and BF7 was recognized by an anti-mEH antibody and that in vitro and in vivo synthesized human mEH is recognized by BF7 and GE2 antibodies. Furthermore, anti-mEH antibody recognizes an antigen expressed both in gliomas and reactive astrocytes, as do BF7 and GE2. Finally, we demonstrate that in contrast to what has been reported in rat embryo fibroblasts, p53 does not regulate mEH mRNA expression in glioma cells.

Immunohistochemical detection of microsomal epoxide hydrolase in human synovial tissue

Microsomal epoxide hydrolase catalyses the hydrolysis of epoxides to water-soluble trans-dihydrodiols. We studied the expression of the hydrolase in synovial tissue samples from patients with osteoarthritis (n = 20), rheumatoid arthritis (n = 36), ankylosing spondylitis (n = 10) or psoriatic arthritis (n = 15) by use of immunohistochemistry with videodensitometric quantification of staining. Strong immunostaining for microsomal epoxide hydrolase was detected in tunica media of synovial blood vessels and moderate staining in synovial lining cells. Experiments with antibodies against CD68 and CLA suggested that both type A (macrophage-like) and type B lining cells (fibroblast-like synoviocytes) express the hydrolase. In addition, some of the subsynovial fibroblast-like cells, histiocytes and monocytes were intensively stained for microsomal epoxide hydrolase. In general, there were no major differences in the intensity of immunostaining for the hydrolase between the diagnostic groups. The enzyme may be involved in local hydrolysis of epoxide metabolites of endo- and xenobiotics in synovial tissue.

Evidence for a leukotriene A4 hydrolase in Xenopus laevis skin exudate

Leukotriene A4 hydrolase is a cytosolic metalloenzyme of the arachidonic acid biosynthetic pathway responsible for leukotriene A4 conversion into leukotriene B4. In addition to its epoxide hydrolase properties, this enzyme exhibits an aminopeptidase activity which was used as an assay to monitor the purification of a novel form of leukotriene A4 hydrolase from Xenopus laevis skin exudate. This 70 kDa, secreted, form of leukotriene A4 hydrolase was identified by immunochemical cross-reactivity with anti-human leukotriene A4 hydrolase antibodies and by its capacity to convert leukotriene A4 into leukotriene B4. Moreover this enzyme produced a second metabolite which could be the leukotriene B4 isomer 5S,12R-dihydroxy-6,10-trans-8,14-4-cis-eicosatetraenoic acid, previously shown by Strömberg et al. (Eur.J. Biochem. 238 (1996) 599-605) to be formed by incubation of the leukotriene A4 with amphibian tissue extracts. Partial amino acid sequencing of peptides generated by endolysin C fragmentation of the purified enzyme confirmed the presence, in X. laevis skin secretions, of a related but distinct form of leukotriene A4 hydrolase which is likely to be responsible for the production of these eicosanoid metabolites of leukotriene A4.

Impact of inherited polymorphisms in glutathione S-transferase M1, microsomal epoxide hydrolase, cytochrome P450 enzymes on DNA, and blood protein adducts of benzo(a)pyrene-diolepoxide

The benzo(a)pyrene (BaP) metabolite benzo(a)pyrenediolepoxide (BPDE) is strongly implicated as a causative agent of lung cancer. To assess the risk of exposure to BaP, we made a combined analysis of levels of BPDE adducts to hemoglobin (Hb), serum albumin (SA), and lymphocyte DNA in 44 patients with incident lung cancer, as a prototype of a population mainly exposed to tobacco-derived BaP. We also investigated whether genetic polymorphisms of cytochrome P450IA1 (CYPIA1), microsomal epoxide hydrolase (mEH), and glutathione S-transferase M1 (GSTM1), which are involved in BaP metabolism, can be determinants of adduct formation. BPDE-Hb, BPDE-SA, and BPDE-DNA adducts were quantified as BaP tetrols released from hydrolysis of macromolecules and measured by high-resolution gas chromatography-negative ion chemical ionization-mass spectrometry to achieve high specificity and sensitivity. Individuals with detectable Hb adducts were positive for SA adducts but not vice versa, suggesting that BPDE-Hb adducts are less informative indicators of BaP exposure. Using PCR methods on DNA, we characterized GSTM1 deletion, CYPIA1 MspI and exon 7 valine variants, and mEH polymorphisms at amino acid positions 113 (EH3) and 139 (EH4). Levels of BPDE adducts were no different among CYPIA1, mEH, and GSTM1 genotypes. However, individuals with measurable BPDE-SA adducts were CYPIA1 variant carriers more frequently (P = 0.03). There was a slightly higher percentage of DNA detectable adducts in subjects with CYPIA1 exon 7 valine polymorphism. When subjects were classified by both polymorphisms on the mEH gene, those with two slow alleles (EH3 homozygous mutated) and no fast alleles (EH4 homozygous wild type) had a lower frequency of BPDE-SA adducts and no DNA adducts (P = 0.06). These results are based on a small number of observations thus far, but this exploratory study suggests that CYPIA1 and mEH variants might have an impact on BPDE exposure markers such as BPDE-SA adducts. Chemical specificity in adduct measurements is important to identify the biomarkers that reflect BaP exposure more accurately.

Differential leukotriene constrictor responses in human atherosclerotic coronary arteries

BACKGROUND

Leukotrienes are a class of biologically active lipids that have potent effects on the heart. To assess their role in coronary artery disease, we compared the contractile responses of leukotriene C4 (LTC4) and leukotriene D4 (LTD4) and their binding activity in both atherosclerotic and nonatherosclerotic human coronary arteries. We also studied expression of the enzymes that control their formation to understand how the 5-lipoxygenase (5-LO) pathway is activated in the coronary arteries.

METHODS AND RESULTS

The capacity of leukotrienes to affect coronary vessel tone and the influence of atherosclerosis was tested in organ baths. Leukotriene receptors were examined by autoradiography, and antibody binding to the various enzymes responsible for their formation was assessed by use of immunocytochemistry. Nonatherosclerotic coronary artery ring segments were unresponsive to LTC4 and LTD4. In contrast, LTC4 and LTD4 induced concentration-dependent contractions in atherosclerotic coronary arteries. Specific [3H]-LTC4 but not LTD4 binding to atherosclerotic coronary artery was evident, with no evidence of specific binding of [3H]-leukotrienes to nonatherosclerotic coronary artery. High-resolution autoradiography identified specific [3H]-LTC4 binding sites to smooth muscle cell and to regions of intimal proliferation and plaque. Cells showing positive antibody binding to 5-LO, FLAP (5-lipoxygenase activating protein), and leukotriene A4 hydrolase were also present in the coronary arteries and had a similar distribution to macrophages.

CONCLUSIONS

Atherosclerosis is associated with a specific leukotriene receptor(s) capable of inducing hyperreactivity of human epicardial coronary arteries in response to LTC4 and LTD4.

Quantification of multiple human cytochrome P450 mRNA molecules using competitive reverse transcriptase-PCR

We developed a quantitative competitive reverse transcriptase-polymerase chain reaction (QC RT-PCR) assay to measure mRNA levels of seven human cytochrome P450 (P450, CYP) genes and microsomal epoxide hydrolase (EH) simultaneously. This assay employs an exogenous recombinant RNA (rcRNA) molecule as an internal standard that shares PCR primer and hybridization probe sequences with CYP1A1, CYP1A2, CYP2A6/7, CYP2D6, CYP2E1, CYP2F1, CYP3A4/5/7, and EH mRNA. Because each rcRNA molecule contains several primer sequences, an entire battery of genes that exhibit differential responsiveness to various classes of xenobiotics may be measured simultaneously from one population of cDNA molecules. In this study, we demonstrated the precision and power of the assay using small amounts of human liver total RNA. We also report for the first time quantitative profiles of P450 and EH mRNA abundance in eight human livers. Cytochrome P450 2E1 mRNA maintained the highest abundance (average 6.67 x 10(7) molecules/microg of total RNA) and least variation (13 fold) in all livers examined. Cytochrome P450 1A2, CYP2A6/7, CYP2D6, CYP3A4/5, and EH mRNAs were approximately one order of magnitude less abundant than CYP2E1 transcripts, with CYP2D6 levels exhibiting the greatest variation (220 fold) between individuals. This QC RT-PCR assay should prove valuable for measuring basal and induced mRNAs in different cell types in vitro, as well as in biomonitoring applications where individuals are exposed or hypersusceptible to certain xenobiotic-initiated toxicities.

Cyclosporin A down-regulates the LTA4 hydrolase level in human keratinocyte cultures

Leukotriene A4 hydrolase is a key enzyme in the biosynthesis of leukotriene B4, a potent pro-inflammatory compound. The purpose of this study was to determine the capacity of antiinflammatory and anti-proliferative compounds to regulate the levels and activity of leukotriene A4 hydrolase in cultured human keratinocytes. The content of leukotriene A4 hydrolase was determined by Western blot analysis, and the activity of leukotriene A4 hydrolase was expressed as the leukotriene B4 formation after incubation of keratinocyte cultures with leukotriene A4. Leukotriene B4 was measured by revered-phase high performance liquid chromatography. Preincubation for 10 min of the cultured keratinocytes with the leukotriene A4 hydrolase inhibitor RP 64699 (0.1-10 microM) caused a significant dose-dependent inhibition of leukotriene B4 formation (IC50 = 0.7 microM). Cyclosporin A (0.1 micrograms/ml and 1.0 micrograms/ml) had no direct effect on leukotriene A4 hydrolase activity, but after incubation for 72 h there was a decrease in the mean leukotriene B4 formation per culture dish (35% and 48%, respectively). The decreased leukotriene B4 formation was caused mainly by a decrease in the mean leukotriene A4 hydrolase content per mg protein (30.1% at 0.1 micrograms/ml cyclosporin A and 40.0% at 1.0 micrograms/ml cyclosporin A), although keratinocyte proliferation was also slightly decreased. Incubations with 1.25-dihydroxyvitamin D3 (10(-7)-10(-10) M), all-trans retinoic acid (10(-6)-10(-10) M), eicosartienoic acid (10(-6)-10(-8) M), dexamethasone (10(-5)-10(-7) M), interferon-gamma (10 and 100 units/ml) or methotrexate (0.1-10 micrograms/ml) had no effect on either the leukotriene B4 formation or the amount of leukotriene A4 hydrolase in keratinocyte cultures. These results show that cyclosporin A, in contrast to other anti-inflammatory and anti-proliferative compounds, inhibits the level of leukotriene A4 hydrolase in keratinocyte cultures. Since similar cyclosporin A concentrations are obtained during treatment of psoriasis with cyclosporin A, the effect on leukotriene A4 hydrolase may play a role in the anti-inflammatory action of cyclosporin A.

Epoxide hydrolase in human and rat peroxisomes: implication for disorders of peroxisomal biogenesis

To understand the basis of excretion of excessive amounts of epoxydicarboxylic fatty acids (EDFA) in urine of patients with disorders of peroxisomal biogenesis (Pitt, J. J., and A. Poulos. 1993. Clin. Chim. Acta. 223: 23-29), the activity of epoxide hydrolase (EH) was measured in cultured skin fibroblasts from control subjects and patients with peroxisomal disorders. EH activity was approximately 40% lower in fibroblasts that lack intact peroxisomes (Zellweger syndrome), whereas the activity in other peroxisomal disorders (X-adrenoleukodystrophy and rhizomelic chondrodysplasia punctata) with intact peroxisomes was similar to control. To identify the specific enzyme/organelle that represents the decrease in EH activity in Zellweger cells, we have analyzed this activity in different subcellular organelles from control and Zellweger skin fibroblasts. EH activity was enriched in peroxisomes from control fibroblast. EH activity in isolated mitochondria, microsomes, or cytosol from Zellweger fibroblast was similar to that of control fibroblast. These observations indicate that deficient activity of EH in cells from Zellweger patients is due to lack of peroxisomal EH activity. The peroxisomal EH is differentially induced to a higher degree by ciprofibrate, a hypolipidemic agent and peroxisome proliferator, than EH activity in other organelles and cytoplasm. The high specific activity of EH in peroxisomes and differential induction of EH activity in peroxisomes as compared to other organelles, and the excretion of EDFA in patients who lack peroxisomes suggests that peroxisomal EH may be responsible for the detoxification of EDFA, and that this enzyme in peroxisomes may be a different protein than the EH found in other organelles.

Improved radiolabeled substrates for soluble epoxide hydrolase

Two rapid assays for the soluble epoxide hydrolase (sEH) are described. First, a sensitive radiometric assay based on thin-layer chromatography of [(14)C]-cis-9,10-epoxystearic acid and its corresponding diol ((14)C]-9,10-dihydroxystearic acid) is described. The cis fatty acid oxide exhibits higher specific activity of hydration with sEH from mouse, rat, human, and potato compared to trans-stilbene oxide (TSO). The K(m) and V(max) obtained for [(14)C]-cis-9,10-epoxystearic acid with mouse sEH are 11.0 microM and 3460 nmol/min/mg protein, respectively. [(14)C]-cis-9,10- Epoxystearic acid might more closely mimic the structures of natural substrates for sEH. Second, [2-(3)H]-trans-1,3-diphenyl-propene oxide ([(3)H]-tDPPO) and [2-(3)H]-cis-1,3-diphenylpropene oxide ([(3)H]-cDPPO) were synthesized and rapid radiometric assays for epoxide hydrolases (EHs) were developed by differential partitioning of the epoxide into iso-octane and its corresponding diol into aqueous phase containing methanol. It was shown that sEHs from mouse, rat, human, and potato rapidly hydrolyze [(3)H]-tDPPO and in comparison to TSO have 20-,49-,28-, and 7-fold higher rates, respectively. Mouse sEH hydrates [(3)H]-tDPPO at 26,200 nmol/min/mg protein, and a K(m)p4 of 2.80 microM is observed.

Fluorometric microassay to quantify microsomal epoxide hydrolase in 96-well plates

The microfluorometric assay, suitable for measuring microsomal epoxide hydrolase activity in cultured cells, is based on the conversion of benzo[a]pyrene-7,8-epoxide to the corresponding trans-benzo[a]pyrene-7,8-dihydrodiol, a compound that fluoresces at 403 nm when excited at 365 nm. Activity is determined by incubating S9 fractions obtained from microcultures with this epoxide and monitoring the fluorescence with a microplate reader. Under the assay conditions selected, the photodecomposition of the reaction product was minimized and the linearity of the reaction was extended. The major advantages of this method are: (1) high sensitivity with a detection limit of 5 pmol/well of trans-benzo[a]pyrene-7,8-dihydrodiol formed, which is comparable to the most sensitive radioactive methods; (2) minimal sample requirement (1-5 micrograms liver microsomes; 10-50 micrograms S9 fraction from cultured cells); (3) reduced consumption of hazardous reagents; and (4) a considerable reduction in assay time and facility for simultaneous determination of enzyme activity in multiple samples.

Distribution of microsomal epoxide hydrolase and glutathione S-transferase in the rat olfactory mucosa: relevance to distribution of lesions caused by systemically-administered olfactory toxicants

This study represents part an of ongoing effort to understand the mechanism underlying the distribution of the olfactory mucosal lesion resulting from the systemic administration of compounds such as 2,6-dichlorobenzonitrile (dichlobenil) and beta,beta'-iminodipropionitrile (IDPN). Immunohistochemistry was performed to localize the microsomal form of epoxide hydrolase (mEH) and glutathione S-transferase (GST) isozymes alpha, mu and pi in the rodent olfactory mucosa. GST-pi was found in abundance in the Bowman's glands of the mucosa lining the dorsal medial meatus (DMM) of the nasal cavity and in the nuclei of basal and sustentacular cells of the dorsal and lateral nasal cavity. Liver and olfactory mucosal levels of mEH are equivalent by Western blot analysis. mEH appeared to be localized in the apical cytoplasm of sustentacular cells in all regions of the olfactory mucosa except for the epithelium lining the DMM. These observations, coupled with the known profile of metabolites for dichlobenil, suggest that systemically-administered compounds causing site-specific lesions in the epithelium lining the DMM of the nasal cavity may do so by the in situ production of reactive epoxide metabolites which are then poorly capable of being detoxified. Thus, the distribution of metabolic enzymes, rather than the absolute level of an enzyme in a tissue, may dictate lesion distribution in the case of toxicants which are bioactivated in target tissues.

Localization of microsomal epoxide hydrolase in normal and neoplastic human kidney

Microsomal epoxide hydrolase is a xenobiotic metabolizing enzyme that catalyzes the conversion of toxic and carcinogenic epoxides to less toxic dihydrodiols. The cellular localization and distribution of microsomal epoxide hydrolase were investigated for the first time in normal and neoplastic human kidney. Light microscopic immunohistochemical studies using an alkaline phosphatase-anti-alkaline phosphatase technique showed that in normal kidney there was a wide distribution of epoxide hydrolase immunoreactivity. The main localization of epoxide hydrolase immunoreactivity was to the proximal and distal tubule epithelial cells. Strong epoxide hydrolase immunoreactivity was also identified in epithelium of the collecting ducts. In addition, epoxide hydrolase immunoreactivity was present in vascular endothelial cells, including endothelial cells lining glomerular capillaries. Epoxide hydrolase immunoreactivity was identified in all the renal tumors, and in each tumor immunoreactivity for epoxide hydrolase was localized to tumor cells. Immunoblotting of both normal kidney and tumor microsomes confirmed the presence of a single protein band of molecular weight 49 KD corresponding to the molecular weight of human hepatic microsomal epoxide hydrolase.

Expression of cytochrome P450 in rat pleural mesothelial cells in secondary cultures

Cultured rat pleural mesothelial cells (RPMC) isolated from male Sprague-Dawley rats have been shown to metabolize polycyclic aromatic hydrocarbons to more oxygenated metabolites. This capacity, which is maintained with passages, suggested the presence of monooxygenase enzymes. In order to clarify the enzymatic pathway, we investigated the expression of cytochromes P450 (CYP) in cultured RPMC by Western and Northern blot analyses. Cells were cultured in Ham's F10 medium supplemented with 10% fetal calf serum. The CYP expression was studied from passage 9 to 16 on different cell strains treated for 48 hours with P450 inducers. CYP1A1 apoprotein expression was very low in untreated cells, but was markedly induced after treatment with 1 microM 3-methylcholanthrene or 22 microM beta-naphthoflavone. CYP1A1 mRNA was not detected in untreated cells and appeared after 3-methylcholanthrene treatment. CYP2E1 apoprotein was constitutively expressed in cultured RPMC, and markedly increased by 170 mM ethanol, and 0.1 microM or 1 microM dexamethasone treatments. Unexpectedly, whereas the amount CYP2E1 mRNA was not modified by ethanol treatment, dexamethasone has a marked inductive effect on CYP2E1 mRNA level. The CYP expression pattern was found similar in RPMC issued from different rats, and not dependent on passage number. The CYP expression and the detection of NADPH-P450 reductase, and of epoxide hydrolase, ascertained that RPMC contain the overall enzymatic pathway required for the biotransformation and activation of procarcinogen compounds, such as polycyclic aromatic hydrocarbons and nitrosamines. Both expression and regulation properties are maintained in long-term cultures of RPMC.

Cytochrome P450 expression in oesophageal cancer

The cytochrome P450 superfamily of enzymes play a central part in the metabolism of carcinogens and anti-cancer drugs. The expression, cellular localisation, and distribution of different forms of P450 and the functionally associated enzymes epoxide hydrolase and glutathione S-transferases have been investigated in oesophageal cancer and non-neoplastic oesophageal tissue using immunohistochemistry. Expression of the different enzymes was confined to epithelial cells in both non-neoplastic samples and tumour samples except the CYP3A was also identified in mast cells and glutathione S-transferase pi was present in chronic inflammatory cells. CYP1A was present in a small percentage of non-neoplastic samples but both CYP2C and CYP3A were absent. Epoxide hydrolase was present in half of the non-neoplastic samples and the different classes of glutathione S-transferase were present in a low number of samples. In carcinomas CYP1A, CYP3A, epoxide hydrolase, and glutathione S-transferase pi were expressed in at least 60% of samples. The expression of glutathione S-transferases alpha and mu were significantly less in adenocarcinoma compared with squamous carcinoma.

Leukotriene A4 hydrolase in human skin

The biochemical properties and immunohistochemical localization of leukotriene (LT) A4 hydrolase were investigated in human skin. The activity of LTA4 hydrolase, which catalyzes the hydrolysis of LTA4 to LTB4, the most chemotactic compound known, was detected in the 100,000 x g supernatant of homogenates of human epidermis and a transformed epidermal cell line (HSC-1). No significant LTA4 hydrolase activity was detected in human whole skin or dermis. The enzymatic properties of LTA4 hydrolase isolated from human keratinocytes and peripheral leukocytes were similar. Their activities were inhibited by bestatin and captopril, and they were completely absorbed by anti-human LTA4 hydrolase antibody. By immunoblotting analysis using this antibody, LTA4 hydrolase was detected as a 70-kDa protein in human epidermis and HSC-1 and was found to be similar to the enzyme detected in peripheral mononuclear leukocytes. In human dermis, LTA4 hydrolase was barely detected by Western blotting. On the other hand, LTA4 hydrolase was demonstrated in the cytoplasm of keratinocytes in the epidermis, and in fibroblasts, infiltrating and endothelial cells in the dermis of normal human skin by immunohistochemical analysis using the immunoperoxidase method. These results suggest that LTB4 can be generated from LTA4 by LTA4 hydrolase in keratinocytes as well as fibroblasts, infiltrating and endothelial cells in the dermis of human skin.

Spectrophotometric substrates for cytosolic epoxide hydrolase

In this study, we demonstrate the utility of a broad class of spectrophotometric substrates for the assay of cytosolic epoxide hydrolase purified from murine liver. These substrates, epoxy esters or carbonates, cyclize spontaneously upon or during hydrolysis of the epoxide functionality. The alcohol released by cyclization may then be assayed directly or by coupling to a second reaction. The alcohol produced, or its secondary reaction products, can be selected to give an absorption in the visible or near-uv range of the spectrum. This allows the synthesis of a wide variety of useful spectrophotometric substrates. 4-Nitrophenyl (2S,3S)-2,3-epoxy-3-phenylpropyl carbonate, at pH 6.4 and 25 degrees C, had a Vmax of 22 mumol min-1 mg-1 and a Km of 16 microM when assayed with a conventional spectrophotometer. When assayed under the same conditions with a 96-well plate reader, the measured Vmax was 15 mumol min-1 mg-1 and the Km was 6.6 microM. Some of these compounds were also found to be substrates for glutathione S-transferase, microsomal epoxide hydrolase, and porcine liver carboxylesterase. Indeed, 4-nitrophenyl 3,4-epoxy-3-phenylbutanoate was a 3.4-fold better substrate for porcine liver carboxylesterase than 4-nitrophenyl acetate when initial rates of hydrolysis were measured under the same conditions.

Xenobiotic metabolising enzyme expression in colonic neoplasia

The cytochrome P450, epoxide hydrolase, and glutathione S-transferase enzyme families play an important part in the metabolism of many carcinogens and anti-cancer drugs. The expression of two forms of cytochrome P450 (P450 1A and P450 3A), epoxide hydrolase and of the alpha, mu, and pi forms of glutathione S-transferase in normal colon, colonic adenomas, and adenocarcinoma of the colon were studied by immunohistochemistry. This allowed the precise cellular site and distribution of each enzyme to be determined. Expression of all the xenobiotic metabolising enzymes studied was almost wholly confined to the epithelial cells, whether in normal, adenoma or carcinoma samples, except that cytochrome P450 3A was also identified in mast cells and glutathione S-transferase pi was also present in chronic inflammatory cells. Cytochrome P450 was present in only a small proportion of normal colon samples, whereas epoxide hydrolase and glutathione S-transferase mu were identified in about half, and glutathione S-transferase alpha and pi in most normal samples. By contrast all the enzyme forms studied were expressed in virtually all adenomas and in over half the carcinomas. These results suggest that cytochrome P450 1A and cytochrome P450 3A are more specific markers of colonic neoplasia than epoxide hydrolase or glutathione S-transferases alpha, mu, and pi.

Differential effects of human recombinant interleukin-1 beta and dexamethasone on hepatic drug-metabolizing enzymes in male and female rats

Interleukin-1 beta (IL-1) is one of the major inflammation mediators, commonly reported to be an inhibitor of hepatic drug metabolism. We studied the effect of IL-1 treatment on various drug-metabolizing enzymes in male and female rats. IL-1 induced both cytochrome P450 (P450) 3A1 activity and protein in females, but in males, IL-1 repressed P450 3A2 activity, without decreasing the protein. P450 1A1 was impaired in males, but was retained after dexamethasone pretreatment. IL-1 did not change P450 2B1/2 activity and protein, but counteracted their induction by dexamethasone. Uridine diphospho-glucuronosyltransferase (UGT) 1A2 (bilirubin) activity and its induction by dexamethasone were not affected by IL-1 treatment. Both P450 2C11 and epoxide hydrolase activities were repressed by IL-1 treatment, and both activities were impaired after dexamethasone treatment. These results clearly demonstrate that IL-1 acts at different steps of protein synthesis and gene expression. The effect of IL-1 on P450 was isoform-dependent, indicating that IL-1 can act on pretranscriptional events. The discrepancy between the variations of the activities and the protein of P450 3A2 suggests a post-translational regulation. For P450 2C11, 3A1, and for microsomal epoxide hydrolase, but not for P450 1A1 and 2B1/2, IL-1 mimics the glucocorticoid effects. These differential effects can affect the kinetics and the bioavailability of drugs used in pathologies in which IL-1 is increased.

Na(+)-dependent bile acid transport by hepatocytes is mediated by a protein similar to microsomal epoxide hydrolase

A protein mediating hepatocyte sodium-dependent bile acid transport across the sinusoidal plasma membrane has been purified by immunoprecipitation with monoclonal antibody (MAb) 25D-1, which specifically recognizes this protein on the surface of intact hepatocytes (Ananthanarayanan et al. J. Biol. Chem. 263: 8338-8343, 1988). The function of this protein was further established by proteoliposome reconstitution (von Dippe et al. J. Biol. Chem. 265: 14812-14816, 1990). NH2-terminal amino acid sequence analysis and amino acid composition revealed this protein to be closely related to the enzyme microsomal epoxide hydrolase (mEH). Both proteins exhibited the same elution times on a reverse-phase high-pressure liquid chromatography column, comigrated with an apparent molecular weight of 49,000 as measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and possessed identical isoelectric points of 8.2. The MAb was capable of immunoprecipitating chromatographically purified mEH, as well as a protein derived from the sinusoidal plasma membrane that exhibited mEH activity comparable to that of the protein isolated from the endoplasmic reticulum. The subtilisin fragmentation patterns derived from chromatographically purified mEH and the MAb-precipitated plasma membrane protein were also identical. Hydropathy profile analysis of the amino acid sequence of mEH suggested the presence of four transmembrane domains. The results of these studies indicate that a protein that is involved in mediating sodium-dependent bile acid transport is closely related to mEH.

The expression of cytochrome P-450, epoxide hydrolase, and glutathione S-transferase in hepatocellular carcinoma

BACKGROUND

Cytochrome P-450, epoxide hydrolase, and glutathione S-transferase (GST) all play a key role in the metabolism of chemical carcinogens, mutagens, and various anti-cancer drugs. All these functionally associated enzymes might be involved in both the development of hepatocellular carcinoma and in determining the anti-cancer drug sensitivity of such tumors.

METHODS

The expression of two forms of cytochrome P-450 (P-450 IA and P-450 IIIA), microsomal epoxide hydrolase, and three classes of cytosolic GST (alpha, mu, and pi) have been studied immunohistochemically in human hepatocellular carcinoma.

RESULTS

The hepatocellular carcinomas were characterized by a consistently high expression of epoxide hydrolase and variable expression of the cytochromes P-450 and GST. Cytochrome P-450 IA and IIIA stained in 64.5% and 41.9% of the 31 hepatocellular carcinomas studied, respectively. Epoxide hydrolase was present in all tumors, and GST types alpha, pi, and mu were identified in 48.4%, 38.7%, and 74.2% of the hepatocellular carcinomas, respectively.

CONCLUSIONS

This study showed that the expression of xenobiotic-metabolizing enzymes in hepatocellular carcinoma is complex and the presence of different xenobiotic enzymes in hepatocellular carcinoma may contribute to the intrinsic drug resistance of these tumors.

Chronic physical activity: hepatic hypertrophy and increased total biotransformation enzyme activity

Does chronic voluntary physical activity alter hepatic or intestinal capacities for xenobiotic biotransformation? This question was investigated by comparing biotransformation enzyme activities in liver and small intestine of active and sedentary rats. Male rats allowed unlimited access to a running wheel and fed ad lib. for 6 weeks were weight-matched to sedentary controls; the active rats ate 22% more food than the sedentary rats (P less than 0.05). Active rats ran 2.8 +/- 0.6 miles/day. Liver weights were higher in the active rats (11.2 +/- 0.2 vs 9.8 +/- 0.2 g; P less than 0.05), as were total liver protein, and liver microsomal and cytosolic protein (P less than 0.05). As a result of liver hypertrophy, the active rats showed higher total liver activity of several biotransformation enzymes, including 2-naphthol sulfotransferase, styrene oxide hydrolase, benzphetamine N-demethylase, ethacrynic acid glutathione S-transferase and morphine UDP-glucuronosyltransferase (P less than 0.05). In contrast, there was no detectable difference in total liver N-acetyltransferase activity toward p-aminobenzoic acid, 2-naphthylamine, and 2-amino-fluorene as well as, relative hepatic enzyme activity (expressed per g liver or per mg protein) and total and relative intestinal enzyme activity. We conclude that chronic voluntary physical activity, accompanied by an increased food intake, results in liver hypertrophy and potentially increases total hepatic capacity to biotransform certain xenobiotic chemicals.

Cigarette smoke inhibits cytosolic but not microsomal epoxide hydrolase of human lung

The effect of cigarette smoke exposure on the activity of cytosolic and microsomal epoxide hydrolase (EH) has been investigated in human lung. Patients were classified as 'recent smokers' (n = 9) or 'non-recent smokers' (n = 10) according to whether they were or were not still smoking 1 month before surgery. Cytosolic EH was measured with [3H]trans-stilbene oxide as a substrate, whereas microsomal EH was measured with [7-3H]styrene oxide as a substrate. Microsomal EH activity did not differ between recent smokers (2.51 +/- 0.93 nmol min-1 mg-1) and non-recent smokers (2.74 +/- 1.10 nmol min-1 mg-1), whereas cytosolic EH activity was significantly lower in recent smokers (6.46 +/- 1.79 pmol min-1 mg-1) than in non-recent smokers (8.41 +/- 2.09 pmol min-1 mg-1, P less than 0.05). Cytosolic EH activity was correlated with the number of days that had passed since the cessation of smoking (r = 0.58, P less than 0.05) and the effect was dose-dependent, since the enzyme activity was inversely correlated with the number of cigarettes smoked per day (r = 0.85, P less than 0.01). This suggests that recent smoking exposure inhibits the activity of cytosolic EH but not microsomal EH, and that the inhibition increases with the number of cigarettes smoked per day. The contribution of cytosolic enzymes to xenobiotic metabolism may be remarkable in extrahepatic tissues. The inhibition of cytosolic EH by tobacco smoke may reduce the inactivation of carcinogenic epoxides in human lung tissues and so may increase a person's susceptibility to lung cancer.

Effects of monoterpenoids on in vivo DMBA-DNA adduct formation and on phase I hepatic metabolizing enzymes

We have previously demonstrated the anticarcinogenic effects of monocyclic monoterpenes such as limonene when given during the initiation phase of 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary cancer in Wistar-Furth (WF) rats. Here we investigated the possible mechanisms for this chemoprevention activity including limonene's effects on DMBA-DNA adduct formation and hepatic metabolism of DMBA. Twenty-four hours after carcinogen administration, there were approximately 50% of the total DMBA-DNA adducts found in control animals formed in the liver, spleen, kidney and lung of limonene-fed animals. While circulating levels of DMBA and/or its metabolites were not different in control and limonene-fed rats, there was a 2.3-fold increase in DMBA and/or DMBA-derived metabolites in the urine of the limonene-fed animals. Studies of the effects of limonene and sobrerol, a hydroxylated monocyclic monoterpenoid with increased chemoprevention activity, on phase I metabolizing enzymes revealed that these terpenoids modulated cytochrome P450 (CYP) and epoxide hydratase (EH) activity. The 5% limonene diet increased total CYP to the same extent as phenobarbital (PB) treatment when compared to control, while 1% sobrerol (isoeffective in chemoprevention to 5% limonene) did not. However, both 5% limonene and 1% sobrerol diets greatly increased the levels of microsomal EH protein and associated hydrating activities towards benzo[a]pyrene 4,5-oxide when compared to control and PB treatment. These changes also modified the rate and regioselectivity of in vitro microsomal DMBA metabolism when compared to PB treatment or control. Identification of the specific isoforms of CYP induced by these terpenoids was performed using antibodies to CYP isozymes in Western blot analysis and inhibition studies of microsomal DMBA metabolism. Five per cent limonene was more effective than 1% sobrerol at increasing the levels of members of the CYP2B and 2C families but was equally effective at increasing EH. Furthermore, both terpenoid diets caused increased formation of the proximate carcinogen, DMBA 3,4-dihydrodiol. While these terpene-induced changes in hepatic CYP and EH do not explain the anticarcinogenic mechanism of these chemopreventive agents, or the ability of limonene systemically to reduce DMBA-DNA binding, they do reveal novel and selective induction mechanisms of hepatic enzymes.

Eicosanoid forming enzyme mRNA in human tissues. Analysis by quantitative polymerase chain reaction

The key enzymes in the formation of eicosanoids, including leukocyte 5-lipoxygenase (5LX), platelet 12-lipoxygenase (12LX), reticulocyte 15-lipoxygenase (15LX), prostaglandin G/H synthase cyclooxygenase, and leukotriene A4 (LTA) hydrolase have been studied extensively in recent years. Little is known, however, about the regulation of these enzymes at the gene level. We have developed a quantitative polymerase chain reaction (PCR) assay to quantify the mRNAs for these five enzymes, as well as for cytoplasmic beta-actin (bACT) mRNA. Human erythroleukemia (HEL) cells, which display megakaryocytic/erythroid characteristics, were selected as a source of RNA to characterize the assay. These cells expressed mRNA for bACT, LTA, cyclooxygenase, and 12LX (in decreasing order). mRNA for 5LX and 15LX was undetectable. Bronchoalveolar lavage fluid cells obtained from asthmatic patients, primarily alveolar macrophages, contained mRNA for bACT, LTA, 5LX, cyclooxygenase, and 15LX (in decreasing order). Treatment of HEL cells with phorbol 12-myristate 13-acetate or steroid administration to asthmatic patients apparently selectively regulated certain of these target genes. The utility of this assay in quantifying mRNA for the various target genes in blood cells, including platelets from patients with chronic myelogenous leukemia, has also been demonstrated. Studies on the regulation of genes for enzymes involved in the leukotriene and prostaglandin biosynthetic pathways, especially when only small tissue samples are available, will be facilitated with this approach.

Studies on the intracellular distributions of soluble epoxide hydrolase and of catalase by digitonin-permeabilization of hepatocytes isolated from control and clofibrate-treated mice

Digitonin permeabilization of hepatocytes from control and clofibrate-treated (0.5% by mass, 10 days) male C57bl/6 mice was used to study the intracellular distributions of soluble ('cytosolic') epoxide hydrolase and of catalase. The following conclusions were drawn. (1) About 60% of the total soluble epoxide hydrolase activity in control mouse hepatocytes is situated in the cytosol. (2) The rest is not mitochondrial, but probably peroxisomal. (3) Of the total catalase activity in control mouse hepatocytes, 5-10% is found in the cytosol. (4) Treatment of mice with clofibrate increases the total hepatocyte activity of soluble epoxide hydrolase 4-fold, but does not influence the relative distribution of this enzyme between cytosol and peroxisomes. (5) The total catalase activity is increased 3.5-fold by clofibrate treatment and 15-35% of this activity is shifted from the peroxisomes to the cytosol.

Possible prognostic value of pulmonary AH-locus-linked enzymes in patients with tobacco-related lung cancer

As prognosis in breast cancer patients has been related to the AHH activity in their breast tissue, we have conducted a similar analysis on pulmonary drug metabolizing enzymes as prognostic markers for male lung cancer patients, primarily investigated for other reasons. A subset of 50 patients with lung cancer related to tobacco use, who had undergone thoracic surgery, was re-analyzed. The activity of parenchymal aryl hydrocarbon hydroxylase (AHH) and epoxide hydrolase (EH) that had been determined previously in homogenates of non-neoplastic surgical lung specimens, was used for comparisons of the patients' survival after surgery. When the crude mortality percentages at 1 and 2 years by AHH or EH activity, subdivided into quarters of the distribution, were calculated, a lower mortality was related to lower enzyme levels. Subjects in the 1st and 4th quarters of the distribution showed significant differences in their 1-year survival for AHH (p = 0.05) and EH (p less than 0.01) activities. This relationship could not be accounted for by age, cumulative lifetime smoking, recent or continuing smoking, stage or histological type of disease. Thus, the levels of pulmonary AHH and EH may have some prognostic significance in tobacco-related lung cancer.