Microsomal Epoxide Hydrolase Activity Research Articles

Tissue-, Region-, and Gene-Specific Induction of Microsomal Epoxide Hydrolase Expression and Activity in the Mouse Intestine by Arsenic in Drinking Water.

This study aimed to characterize the effects of arsenic exposure on the expression of microsomal epoxide hydrolase (mEH or EPHX1) and soluble epoxide hydrolase (sEH or EPHX2) in the liver and small intestine. C57BL/6 mice were exposed to sodium arsenite in drinking water at various doses for up to 28 days. Intestinal, but not hepatic, mEH mRNA and protein expression was induced by arsenic at 25 ppm, in both males and females, whereas hepatic mEH expression was induced by arsenic at 50 or 100 ppm. The induction of mEH was gene specific, as the arsenic exposure did not induce sEH expression in either tissue. Within the small intestine, mEH expression was induced only in the proximal, but not the distal segments. The induction of intestinal mEH was accompanied by increases in microsomal enzymatic activities toward a model mEH substrate, cis-stilbene oxide, and an epoxide-containing drug, oprozomib, in vitro, and by increases in the levels of PR-176, the main hydrolysis metabolite of oprozomib, in the proximal small intestine of oprozomib-treated mice. These findings suggest that intestinal mEH, playing a major role in converting xenobiotic epoxides to less reactive diols, but not sEH, preferring endogenous epoxides as substrates, is relevant to the adverse effects of arsenic exposure, and that further studies of the interactions between drinking water arsenic exposure and the disposition or possible adverse effects of epoxide-containing drugs and other xenobiotic compounds in the intestine are warranted. SIGNIFICANCE STATEMENT: Consumption of arsenic-contaminated water has been associated with increased risks of various adverse health effects, such as diabetes, in humans. The small intestinal epithelial cells are the main site of absorption of ingested arsenic, but they are not well characterized for arsenic exposure-related changes. This study identified gene expression changes in the small intestine that may be mechanistically linked to the adverse effects of arsenic exposure and possible interactions between arsenic ingestion and the pharmacokinetics of epoxide-containing drugs in vivo.

Ibuprofen alters epoxide hydrolase activity and epoxy-oxylipin metabolites associated with different metabolic pathways in murine livers

Over the last decade oxylipins have become more recognized for their involvement in several diseases. Non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen are known to inhibit cyclooxygenase (COX) enzymes, but how NSAIDs affect oxylipins, in addition to COX products, in animal tissues is not well understood. Oxylipins in livers from male and female mice treated with 100 mg/kg/day of ibuprofen for 7 days were investigated. The results showed that ibuprofen treated male livers contained 7 times more altered oxylipins than ibuprofen treated female livers. In male and female livers some prostaglandins were altered, while diols, hydroxy fatty acids and epoxides were significantly altered in male livers. Some soluble epoxide hydrolase (sEH) products, such as 9,10-DiHODE were found to be decreased, while sEH substrates (such as 9(10)-EpODE and 5(6)-EpETrE) were found to be increased in male livers treated with ibuprofen, but not in ibuprofen treated female livers. The enzymatic activities of sEH and microsomal epoxide hydrolase (mEH) were elevated by ibuprofen in both males and females. Analyzing the influence of sex on the effect of ibuprofen on oxylipins and COX products showed that approximately 27% of oxylipins detected were influenced by sex. The results reveal that ibuprofen disturbs not only the COX pathway, but also the CYP450 and lipoxygenase pathways in male mice, suggesting that ibuprofen is likely to generate sex related differences in biologically active oxylipins. Increased sEH activity after ibuprofen treatment is likely to be one of the mechanisms by which the liver reduces the higher levels of EpODEs and EpETrEs.

Polymorphisms in the microsomal epoxide hydrolase gene: role in lung cancer susceptibility and prognosis.

The aim of this study was to investigate the relationship between EPHXI exon 3 Tyr113His and exon 4 His139Arg polymorphisms, predicted microsomal epoxide hydrolase (mEH) activity, and lung cancer development. mEH is a protective enzyme involved in oxidative defences against a number of environmental chemicals and pollutants, but it is also responsible for the xenobiotic activation of carcinogens. We investigated the two polymorphisms of the mEH gene (EPHX1) in 58 lung cancer patients and 41 controls using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The exon 3 Tyr113His polymorphism was associated with lung cancer (P < 0.001). The frequency of the His113His homozygote genotype in exon 3 was significantly increased in patients compared with controls (P < 0.001). In contrast, there was no significant difference in exon 4 polymorphisms between patients and controls. When the exon 3 and 4 polymorphisms were considered together, the combined EPHX1 His113His113/His139His139 genotype (very low predicted enzyme activity) was found to be associated with an increased risk of lung cancer (P = 0.044, OR = 3.063, CI = 0.932-10.069). We observed that patients with T3 + T4 tumors had an approximately 3-fold higher risk of the Tyr113/His113 genotype than patients with T1 + T2 tumors. Lung cancer patients carrying a heterozygote Tyr113/His 113 genotype had a 2-fold increased risk of lymph node metastases (P = 0.051). These findings suggest that the exon 3 Tyr113His and exon 4 His139Arg polymorphisms of EPHXI may be associated with a increased risk of lung cancer and a worse prognosis.

Polymorphic Variants of SCN1A and EPHX1 Influence Plasma Carbamazepine Concentration, Metabolism and Pharmacoresistance in a Population of Kosovar Albanian Epileptic Patients.

AimThe present study aimed to evaluate the effects of gene variants in key genes influencing pharmacokinetic and pharmacodynamic of carbamazepine (CBZ) on the response in patients with epilepsy.Materials & MethodsFive SNPs in two candidate genes influencing CBZ transport and metabolism, namely ABCB1 or EPHX1, and CBZ response SCN1A (sodium channel) were genotyped in 145 epileptic patients treated with CBZ as monotherapy and 100 age and sex matched healthy controls. Plasma concentrations of CBZ, carbamazepine-10,11-epoxide (CBZE) and carbamazepine-10,11-trans dihydrodiol (CBZD) were determined by HPLC-UV-DAD and adjusted for CBZ dosage/kg of body weight.ResultsThe presence of the SCN1A IVS5-91G>A variant allele is associated with increased epilepsy susceptibility. Furthermore, carriers of the SCN1A IVS5-91G>A variant or of EPHX1 c.337T>C variant presented significantly lower levels of plasma CBZ compared to carriers of the common alleles (0.71±0.28 vs 1.11±0.69 μg/mL per mg/Kg for SCN1A IVS5-91 AA vs GG and 0.76±0.16 vs 0.94±0.49 μg/mL per mg/Kg for EPHX1 c.337 CC vs TT; P<0.05 for both). Carriers of the EPHX1 c.416A>G showed a reduced microsomal epoxide hydrolase activity as reflected by a significantly decreased ratio of CBZD to CBZ (0.13±0.08 to 0.26±0.17, p<0.05) also of CBZD to CBZE (1.74±1.06 to 3.08±2.90; P<0.05) and CDRCBZD (0.13±0.08 vs 0.24±0.19 μg/mL per mg/Kg; P<0.05). ABCB1 3455C>T SNP and SCN1A 3148A>G variants were not associated with significant changes in CBZ pharmacokinetic. Patients resistant to CBZ treatment showed increased dosage of CBZ (657±285 vs 489±231 mg/day; P<0.001) but also increased plasma levels of CBZ (9.84±4.37 vs 7.41±3.43 μg/mL; P<0.001) compared to patients responsive to CBZ treatment. CBZ resistance was not related to any of the SNPs investigated.ConclusionsThe SCN1A IVS5-91G>A SNP is associated with susceptibility to epilepsy. SNPs in EPHX1 gene are influencing CBZ metabolism and disposition. CBZ plasma levels are not an indicator of resistance to the therapy.

A novel activity of microsomal epoxide hydrolase: metabolism of the endocannabinoid 2-arachidonoylglycerol

Microsomal epoxide hydrolase (EPHX1, EC 3.3.2.9) is a highly abundant α/β-hydrolase enzyme that is known for its catalytical epoxide hydrolase activity. A wide range of EPHX1 functions have been demonstrated including xenobiotic metabolism; however, characterization of its endogenous substrates is limited. In this study, we present evidence that EPHX1 metabolizes the abundant endocannabinoid 2-arachidonoylglycerol (2-AG) to free arachidonic acid (AA) and glycerol. The EPHX1 metabolism of 2-AG was demonstrated using commercially available EPHX1 microsomes as well as PC-3 cells overexpressing EPHX1. Conversely, EPHX1 siRNA markedly reduced the EPHX1 expression and 2-AG metabolism in HepG2 cells and LNCaP cells. A selective EPHX1 inhibitor, 10-hydroxystearamide, inhibited 2-AG metabolism and hydrolysis of a well-known EPHX1 substrate, cis-stilbene oxide. Among the inhibitors studied, a serine hydrolase inhibitor, methoxy-arachidonyl fluorophosphate, was the most potent inhibitor of 2-AG metabolism by EPHX1 microsomes. These results demonstrate that 2-AG is an endogenous substrate for EPHX1, a potential role of EPHX1 in the endocannabinoid signaling and a new AA biosynthetic pathway.

DNA Damage and Susceptibility Assessment in Industrial Workers Exposed to Styrene

Styrene is a widely used chemical in the manufacture of synthetic rubber, resins, polyesters, and plastics. The highest levels of human exposure to styrene occur during the production of reinforced plastic products. The objective of this study was to examine occupational exposure to styrene in a multistage approach, in order to integrate the following endpoints: styrene in workplace air, mandelic and phenylglyoxylic acids (MA + PGA) in urine, sister chromatid exchanges (SCE), micronuclei (MN), DNA damage (comet assay), and genetic polymorphisms of metabolizing enzymes (CYP2E1, EPHX1, GSTM1, GSTT1, and GSTP1). Seventy-five workers from a fiberglass-reinforced plastics factory and 77 unexposed controls took part in the study. The mean air concentration of styrene in the breathing zone of workers (30.4 ppm) and the mean concentration of urinary metabolites (MA + PGA = 443 ± 44 mg/g creatinine) exceeded the threshold limit value (TLV) and the biological exposure index (BEI). Significantly higher SCE frequency rate and DNA damage were observed in exposed workers, but MN frequency was not markedly modified by exposure. With respect to the effect of genetic polymorphisms on different exposure and effect biomarkers studied, an increase in SCE levels with elevated microsomal epoxide hydrolase activity was noted in exposed workers, suggesting a possible exposure–genotype interaction.

Genetically Lowered Microsomal Epoxide Hydrolase Activity and Tobacco-Related Cancer in 47,000 Individuals

Two functional polymorphisms of the microsomal epoxide hydrolase (mEH) gene (EPHX1), Tyr113His (rs1051740) and His139Arg (rs2234922), have variably been found to influence susceptibility to various cancer forms. We tested whether genetically lowered mEH activity affects risk of developing cancer in the general population. We genotyped 47,089 individuals from the Danish general population for the Tyr113His and His139Arg polymorphisms in the EPHX1 gene and divided them into groups with predicted fast, intermediate, and slow mEH activity. Using Cox proportional hazards models, we calculated HRs for 26 individual cancer diagnoses and for groups of any cancer, tobacco-related cancers, estrogen-related female cancers, and other cancers. Of the 47,089 individuals, 7,590 experienced a cancer event, and of these, 1,466 were tobacco-related. After multifactorial adjustment, the HRs (95% CI) for tobacco-related cancer were 1.1 (0.8-1.5) and 1.5 (1.1-2.0) in individuals with intermediate and slow mEH activity versus individuals with the fast phenotype (P(trend) = 0.003). The corresponding HRs among ever-smokers were 1.1 (0.8-1.5) and 1.5 (1.1-2.0; P(trend) = 0.003), whereas HRs among never-smokers did not differ from 1.0. Our results indicate that genetically lowered mEH activity is associated with increased risk of developing tobacco-related cancer among smokers in the general population; however, additional studies are needed to confirm our findings. To our knowledge, this is the largest study to investigate the association of mEH phenotype and genotype with tobacco-related cancers combined in the general population.

Common polymorphisms in the microsomal epoxide hydrolase and N-acetyltransferase 2 genes in association with inflammatory bowel disease in the Danish population

Chronic inflammatory bowel disease (IBD) is characterized by recurrent inflammation of the intestinal mucosa. Reactive molecules play a central role in altering the intestinal permeability, which may induce or sustain an immune response. Changes in detoxification of substances that causes epithelial damage may confer susceptibility to IBD. Hence, polymorphic enzymes involved in the detoxification processes may be risk factors of IBD. The two biotransformation enzymes microsomal epoxide hydrolase and N-acetyltransferase 2 were genotyped using TaqMan based real-time PCR in 388 patients with Crohn's disease, 565 patients with ulcerative colitis and 796 healthy controls. No association was found between the genotypes of low microsomal epoxide hydrolase activity or slow N-acetyltransferase 2 acetylator status and IBD. An association was found between microsomal epoxide hydrolase and less than 40 years of age at diagnosis of Crohn's disease and microsomal epoxide hydrolase and azathiporine use in patients with ulcerative colitis. No other evident phenotypic associations were found for the two enzymes and either ulcerative colitis or Crohn's disease. A possible modification of smoking on microsomal epoxide hydrolase genotypes was found. Microsomal epoxide hydrolase and N-acetyltransferase 2 genotypes appear not to be individual risk factors of IBD, or to be important in relation to phenotypic characteristics of IBD.

Induction of epoxide hydrolase and glucuronosyl transferase by isothiocyanates and intact glucosinolates in precision-cut rat liver slices: importance of side-chain substituent and chirality

The potential of three isothiocyanates, namely R,S-sulforaphane, erucin and phenethyl isothiocyanate, of two naturally occurring glucosinolates, namely glucoerucin and glucoraphanin, and of the enantiomers of sulforaphane to modulate glucuronosyl transferase and epoxide hydrolase, two major carcinogen-metabolising enzyme systems, was investigated in precision-cut rat liver slices. Following exposure of the slices to the isothiocyanates (0-25μM), erucin and phenethyl isothiocyanate, but not R,S-sulforaphane, elevated glucuronosyl transferase and epoxide hydrolase activities and expression, determined immunologically. Of the two enantiomers of sulforaphane, the R-enantiomer enhanced, whereas the S-enantiomer impaired, glucuronosyl transferase activity and only the former increased protein expression; furthermore, R-sulforaphane was more effective than the S-enantiomer in up-regulating microsomal epoxide hydrolase. When precision-cut rat liver slices were exposed to the same concentrations of glucoerucin and glucoraphanin, both glucosinolates caused a marked increase in the activity and expression of the microsomal epoxide hydrolase but had no effect on glucuronosyl transferase activity. It may be inferred that the ability of isothiocyanates to enhance hepatic microsomal epoxide hydrolase and glucuronosyl transferase activities is dependent on the nature of the side chain. Moreover, in the case of sulforaphane, the naturally occurring R-enantiomer increased both activities, whereas, in contrast, activities were impaired in the case of the S-enantiomer. Finally, intact glucosinolates are potent inducers of epoxide hydrolase and can thus contribute directly to the chemopreventive potential associated with cruciferous vegetable consumption.

Polymorphisms in the Microsomal Epoxide Hydrolase Gene: Role in Lung Cancer Susceptibility and Prognosis

The aim of this study was to investigate the relationship between EPHXI exon 3 Tyr113His and exon 4 His139Arg polymorphisms, predicted microsomal epoxide hydrolase (mEH) activity, and lung cancer development. mEH is a protective enzyme involved in oxidative defences against a number of environmental chemicals and pollutants, but it is also responsible for the xenobiotic activation of carcinogens. We investigated the two polymorphisms of the mEH gene (EPHX1) in 58 lung cancer patients and 41 controls using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The exon 3 Tyr113His polymorphism was associated with lung cancer (P < 0.001). The frequency of the His113His homozygote genotype in exon 3 was significantly increased in patients compared with controls (P < 0.001). In contrast, there was no significant difference in exon 4 polymorphisms between patients and controls. When the exon 3 and 4 polymorphisms were considered together, the combined EPHX1 His113His113/His139His139 genotype (very low predicted enzyme activity) was found to be associated with an increased risk of lung cancer (P = 0.044, OR = 3.063, CI = 0.932-10.069). We observed that patients with T3 + T4 tumors had an approximately 3-fold higher risk of the Tyr113/His113 genotype than patients with T1 + T2 tumors. Lung cancer patients carrying a heterozygote Tyr113/His 113 genotype had a 2-fold increased risk of lymph node metastases (P = 0.051). These findings suggest that the exon 3 Tyr113His and exon 4 His139Arg polymorphisms of EPHXI may be associated with a increased risk of lung cancer and a worse prognosis.

Effects of isatin‐isoniazid derivatives on drug metabolizing and chemoprotective enzymes in mice

AbstractFour isatin‐isoniazid derivatives with proven efficacy against resistant strains of Mycobacterium tuberculosis, that had greater lipophilicity than isoniazid were evaluated for effects on hepatic drug metabolizing and chemoprotective enzymes and compared to isoniazid. Following intragastric administration to mice (75 or 150 mg/kg×3 days), none of the four compounds exhibited hepatotoxicity, and only isoniazid was found to elevate CYP2E1 activity. All compounds slightly elevated Cyp1a1/2 mRNA levels, but these did not result in increased methoxyresorufin demethylase activity. With the exception of isoniazid, approximately twofold elevations in Ugt1a mRNAs (seen with isatin‐isoniazid [Ugt1a1, Ugt1a6, Ugt1a9], 1‐propynylisatin‐isoniazid [Ugt1a1, Ugt1a9], and 1‐propylisatin‐isoniazid [Ugt1a1]) also did not result in changes in 4‐nitrophenol glucuronidation activity. 1‐Benzylisatin‐isoniazid was the only compound that (1) elevated Ugt2b5 mRNA, and (2) like isoniazid, had no effect on glutathione transferase activities and mRNAs. 1‐Propynylisatin‐isoniazid elevated glutathione transferase activity toward 1‐chloro‐2,4‐dinitrobenzene, 1‐propylisatin‐isoniazid decreased the 2.4‐kb Gstp transcript, and isatin‐isoniazid increased Gsta, Gstm, and the 1.2‐kb Gstp transcripts. None of the four compounds affected glutathione peroxidase activity, although 1‐propynylisatin‐isoniazid and 1‐benzylisatin‐isoniazid elevated mRNA transcripts. None of the four compounds affected microsomal epoxide hydrolase or thioredoxin reductase activities but, in parallel, isoniazid, 1‐propynylisatin‐isoniazid, and 1‐propylisatin‐isoniazid elevated mRNAs of each. 1‐Propynylisatin‐isoniazid, 1‐propylisatin‐isoniazid, and 1‐benzylisatin‐isoniazid, and isoniazid, elevated quinone oxidoreductase (Nqo1) mRNA, but only 1‐propylisatin‐isoniazid elevated the activity. Altogether, and despite some changes in mRNA expression, the novel isatin‐isoniazid derivatives had only minor effects on mouse hepatic enzyme activities and are worthy of further investigation as possible therapeutic agents likely free of major induction‐related drug–drug interactions. Drug Dev Res 2010. © 2010 Wiley‐Liss, Inc.

EPHX1 polymorphisms, COPD and asthma in 47,000 individuals and in meta-analysis

We tested the hypothesis that two well-characterised functional polymorphisms of the microsomal epoxide hydrolase gene (EPHX1), T113C and A139G, may influence susceptibility to chronic obstructive pulmonary disease (COPD) and asthma. We genotyped participants from the Copenhagen City Heart Study (n = 10,038) and the Copenhagen General Population Study (n = 37,022) for the T113C and A139G variants in the EPHX1 gene and measured lung function and recorded COPD hospitalisation and asthma and smoking history. Finally, we meta-analysed results from 19 studies including 7,489 COPD cases and 42,970 controls. The OR for spirometry-defined COPD or COPD hospitalisation did not differ from 1.0 for any of the EPHX1 genotypes or phenotypes overall, or in smokers or nonsmokers separately (p-value for trend 0.18-0.91). Likewise, EPHX1 genotypes or phenotypes did not associate with risk of asthma (p-value for trend 0.46-0.98). In meta-analysis, random effects OR for COPD in T113C heterozygotes and homozygotes versus non-carriers were 1.17 (0.99-1.38) and 1.38 (1.09-1.74), respectively. Corresponding values for A139G were 0.93 (0.83-1.05) and 0.89 (0.78-1.02). Our results indicate that genetically reduced microsomal epoxide hydrolase activity is not a major risk factor for COPD or asthma in the Danish population; however, meta-analysis cannot completely exclude a minor effect on COPD risk.

Influence of Some Detoxification Enzyme Polymorphisms on Cytogenetic Biomarkers Between Individuals Exposed to Very Low Doses of 1,3-Butadiene

To evaluate the variation of some biomarkers related to the level of enzymatic activity dependent on the different polymorphisms. We studied 27 butadiene-exposed workers and 37 controls using different biomarkers of the genotoxic effect. The genotypes were determined using polymerase chain reaction and restriction fragment length polymorphism-polymerase chain reaction techniques; the subjects were assigned to a specific group based on the microsomal epoxide hydrolase (mEH) activity predicted by their genotype (low, intermediate, high). The studied biomarkers were not able to discriminate between exposed and control individuals, but sister chromatid exchange (SCE) and high frequency cells were influenced by smoking habits. Smokers having fast microsomal epoxide hydrolase activity showed higher SCE frequency (7.61) respect to those presenting intermediate (5.86) or slow (6.65) enzymatic activity. On the basis of these results, can we suppose the existence of an "intermediate genotype" advantage (at least for induction of SCE)?

A Long-Wavelength, Fluorogenic Probe for Epoxide Hydrolase: 7-(2-(Oxiran-2-yl)ethoxy) Resorufin

Epoxide hydrolase plays an important role in the detoxification of genotoxic compounds and in the control of physiological signaling molecules. Altered levels of epoxide hydrolase activity are associated with many diseases, such as emphysema, lung cancer, ovarian cancer, and laryngeal carcinoma. We designed and synthesized a resorufin-based fluorogenic probe, 7-(2-(oxiran-2-yl)ethoxy) resorufin, which was hydrolyzed by microsomal epoxide hydrolase to form the corresponding diol, which upon further treatment with sodium periodate released the strongly fluorescent resorufin. The probe exhibits good biological compatibility and photophysical properties, such as long wavelength excitation (571 nm) and emission (585 nm) and a wide working pH range (from 6.0 to 10.0), and thus facilitates the determination of the activity of microsomal epoxide hydrolase.

Regulation of ATP‐binding cassette (Abc) transporters by organoselenium compounds

Selenium‐containing compounds have demonstrated chemopreventive activity in a variety of chemically‐induced tumor models, but a unifying mechanism for this effect remains elusive. Altered disposition of chemicals and toxic metabolites may be contributing factors. Following dietary ingestion of selenocysteine pro‐drugs and selenocystine (15 ppm Se) for 1 month, mouse hepatic glutathione transferase, quinone oxidoreductase and microsomal epoxide hydrolase activities were elevated by 2‐butyl‐ and 2‐oxoselenazolidine‐4‐carboxylic acids (SCAs) and selenocystine, but not by 2‐cyclohexyl‐, 2‐phenyl‐, and 2‐(2′‐hydroxyphenyl)‐ SCAs. Expression of multidrug resistance‐associated proteins and other Abc transporters were evaluated by qPCR. Of 10 transporters examined, none responded in a pattern similar to the activities of the enzymes capable of being regulated via the Nrf2/ARE mechanism. Abcc3 (Mrp3) was increased only by 2‐butylSCA and no transporters were induced by 2‐oxoSCA or selenocystine. 2‐(2′‐Hydroxyphenyl)SCA was the only compound that induced expression of Abcc2 (Mrp2) and Abcb6. All the selenocompounds reduced the expression of Abcb11. Expression of Abcc1, Abcc4, Abcc5, Abcc6, and Abcg2 and Abca3, was not altered by any compound. Selenocompound regulation of Abc transporter expression appears to be compound dependent and unrelated to the Nrf2/ARE pathway.Support: GM 058913

A fluorescent micro‐assay utilizing purified microsomal epoxide hydrolase

A low volume (10 μL) kinetic fluorescent assay to evaluate human microsomal epoxide hydrolase (mEH) activity with the α‐cyano‐methyl ester substrate, PHOME (Analyt. Biochem. (2006) 355, 71–80), has been optimized. mEH was successfully cloned into a mammalian expression vector, expressed transiently in FreeStyle 293F cells, and purified by affinity chromatography (purity &gt; 80%). In the presence of 5 μM PHOME, reaction rates were linearly proportional to added enzyme to 0.1 μM and the reactions were linear for up to 60 minutes with respect to product formation. The lowest discernable reaction rate of 5.5 nM/min was obtained with 10 nM mEH; with an assay signal:noise of 3:1. Optimized assay buffer contained 25 mM HEPES pH 7.0, 0.01% CHAPS, and 0.005% casein. Purified mEH activity was selectively inhibited with the addition of 50 mM ZnSO4 or with the known mEH inhibitor, Valpromide (IC50 = 1 mM and 5 μM, respectively), indicating that product formation was due solely to mEH. The potency of Valpromide was shown to give similar values in an alternative assay format using mEH enriched microsomes (IC50 = 8.0 μM). AUDA, a potent sEH inhibitor, was not an inhibitor of purified mEH. Thus, purified mEH provides a means to develop a low volume, high throughput assay to further our efforts towards developing inhibitors that can selectively discriminate sEH versus mEH activity.

Differential response of human and rat epoxide hydrolase to polycyclic aromatic hydrocarbon exposure: Studies using precision-cut tissue slices

The potential of polycyclic aromatic hydrocarbons (PAHs) to modulate microsomal epoxide hydrolase activity, determined using benzo[a]pyrene 5-oxide as substrate, in human liver, was evaluated and compared to rat liver. Precision-cut liver slices prepared from fresh human liver were incubated with six structurally diverse PAHs, at a range of concentrations, for 24h. Of the six PAHs studied, benzo[a]pyrene, dibenzo[a,h]anthracene and fluoranthene gave rise to a statistically significant increase in epoxide hydrolase activity, which was accompanied by a concomitant increase in epoxide hydrolase protein levels determined by immunoblotting. The other PAHs studied, namely dibenzo[a,l]pyrene, benzo[b]fluoranthene and 1-methylphenanthrene, influenced neither activity nor enzyme protein levels. When rat slices were incubated under identical conditions, only benzo[a]pyrene and dibenzo[a,h]anthracene elevated epoxide hydrolase activity, which was, once again accompanied by a rise in protein levels. At the mRNA level, however, all six PAHs caused an increase, albeit to different extent. In rat, epoxide hydroxylase activity in lung slices was much lower than in liver slices. In lung slices, epoxide hydrolase activity was elevated following exposure to benzo[a]pyrene and dibenzo[a,l]pyrene and, to a lesser extent, 1-methylphenanthrene; similar observations were made at the protein level. At both activity and protein levels extent of induction was far more pronounced in the lung compared with the liver. It is concluded that epoxide hydrolase activity is an inducible enzyme by PAHs, in both human and rat liver, but induction potential by individual PAHs varies enormously, depending on the nature of the compound involved. Marked tissue differences in the nature of PAHs stimulating activity in rat lung and liver were noted. Although in the rat basal lung epoxide hydrolase activity is much lower than liver, it is more markedly inducible by PAHs.

Cytogenetic and molecular biomonitoring of a Portuguese population exposed to pesticides

Widespread use of pesticides in agriculture represents a threat not only to the environment but also to human populations exposed to them. Many of these compounds are capable of inducing mutations in DNA and lead to several diseases including cancer. In the present study, cytogenetic damage in peripheral lymphocytes from 33 farmers of Oporto district (Portugal) exposed to pesticides was evaluated by means of micronuclei (MN), sister chromatid exchange (SCE) and chromosomal aberrations (CA). In addition, effect of polymorphic genes of xenobiotic metabolizing enzymes (GSTM1, GSTT1, GSTP1, CYP2E1 and EPHX1) was also evaluated. A non-exposed group from the same area and with same demographic characteristics without exposure to genotoxic compounds was studied and data obtained from both groups was compared. MN and SCE frequencies were significantly higher in the exposed group (P < 0.005). In what concerns CA results, no significant differences were observed. It was possible to relate a specific working environment (greenhouses) with higher levels of genetic damage. Use of personal protective equipment revealed to be important to prevent exposure and diminish genetic damage inflicted by pesticides. Allele frequencies of studied polymorphic genes obtained in this study are similar to the ones described by other authors for Caucasian populations. Despite the low number of subjects, results suggest that low mEH (microsomal epoxide hydrolase) activity as well as GSTT1 positive genotype are associated with increased cytogenetic damage.

Genetic variations in benzene metabolism and susceptibility to multiple myeloma

We have previously shown that deficiency in the biotransformation enzyme glutathione- S-transferase theta (GSTT1) is a risk factor for multiple myeloma (MM). The present case–control study of 102 MM patients and 205 controls revealed a significant trend in increasing risk of MM with inheritance of multiple putative ‘high risk’ genetic variants in related pathways of benzene detoxification. Individuals who carried polymorphisms for GSTT1 null and/or high activity microsomal epoxide hydrolase ( mEH 113YY + 139HR or 113YY + 139RR or 113YH + 139RR) and/or low activity NAD(P)H:quinone oxidoreductase 1 (NQO1 187PS/SS) were 1.65, 2.49 and 13 times more likely to have MM ( P trend = 0.001).

Xenobiotic conjugation systems in deer compared with cattle and rat

The ability of cattle and deer liver to catalyse xenobiotic conjugation reactions was investigated and compared with that of the rat. Marked differences in the activity of these enzymes were noted between the domestic animals and rats. Hepatic microsomal epoxide hydrolase activity in cattle and deer, determined using benzo[ a]pyrene 4,5-oxide as substrate, was nearly twice that of the rat. In contrast, glutathione S-transferase activity in hepatic cytosol, determined with 1-chloro-2,4-dinitrobenzene as substrate, was significantly lower in the cattle and deer. When 1,2-dichloro-4-nitrobenzene served as the accepting substrate, no activity was detectable in the cattle and deer. Similarly, glutathione reductase activity and total glutathione levels were markedly lower in the cattle and deer compared with the rat. Cytosolic sulfotransferase activity, monitored using 2-naphthol as substrate, was higher in cattle compared with the rat. Finally, microsomal UDP-glucuronosyl transferase activity, determined using 1-napththol as substrate, did not differ significantly among the three species.