Hepatic epoxide hydrolase activities and their induction by clofibrate and diethylhexylphthalate in various strains of mice

Multiple transcriptomic profiling: potential novel metabolism-related genes predict prepubertal testis damage caused by DEHP exposure

The toxic effect of di(2-ethylhexyl) phthalate (DEHP) on prepubertal testes was examined in this study. We treated 3-week-old male mice with 4.8 mg/kg/day (milligram/kilogram/day) (no observed adverse effect level), 30 mg/kg/day (high exposure dose relative to humans), 100 mg/kg/day (level causing a reproductive system disorder), and 500 mg/kg/day (dose causing a multigenerational reproductive system disorder) of DEHP via gavage. Obvious abnormalities in the testicular organ coefficient, spermatogenic epithelium, and testosterone levels occurred in the 500 mg/kg DEHP group. Ribonucleic acid sequencing (RNA-seq) showed that differentially expressed genes (DEGs) in each group could enrich reproduction and reproductive process terms according to the gene ontology (GO) results, and coenrichment of metabolism pathway was observed by the Reactome pathway analysis. Through the analysis of common genes in the metabolism pathway, we discovered that DEHP exposure at 4.8 to 500 mg/kg or 100 mg/kg caused the same damages to the prepubertal testis. In general, we identified two key transcriptional biomarkers (fatty acid binding protein 3 (Fabp3) and carboxylesterase (Ces) 1d), which provided new insight into the gene regulatory mechanism associated with DEHP exposure and will contribute to the prediction and diagnosis of prepuberty testis injury caused by DEHP.

Peroxisomal proteomics, a new tool for risk assessment of peroxisome proliferating pollutants in the marine environment

In an attempt to improve the detection of peroxisome proliferation as a biomarker in environmental pollution assessment, we have applied a novel approach based on peroxisomal proteomics. Peroxisomal proteins from digestive glands of mussels Mytilus galloprovincialis were analyzed using 2-DE and MS. We have generated a reference 2-DE map from samples obtained in a well-studied reference area and compared this with peroxisomal proteomes from other sequenced genomes. In addition, by comparing 2-DE maps from control samples with samples obtained in a polluted area, we have characterized the peroxisome proliferation expression pattern associated with exposure to a polluted environment. Over 100 spots were reproducibly resolved per 2-DE map; 55 differentially expressed spots were quantitatively detected and analyzed, and 14 of these showed an increase in protein expression of more than fourfold. Epoxide hydrolase, peroxisomal antioxidant enzyme, and sarcosine oxidase (SOX) have been identified by ESI MS/MS, and acyl-CoA oxidase, multifunctional protein, and Cu,Zn-superoxide dismutase were immunolocalized by Western blotting. Our results indicate that a peroxisomal protein pattern associated to marine pollutant exposure can be generated, and this approach may have a greater potential as biomarker than traditional, single-protein markers.

Differential subcellular localization of endogenous and transfected soluble epoxide hydrolase in mammalian cells: evidence for isozyme variants

Endogenous, constitutive soluble epoxide hydrolase in mice 3T3 cells was localized via immunofluorescence microscopy exclusively in peroxisomes, whereas transiently expressed mouse soluble epoxide hydrolase (from clofibrate-treated liver) accumulated only in the cytosol of 3T3 and HeLa cells. When the C-terminal lie of mouse soluble epoxide hydrolase was mutated to generate a prototypic putative type 1 PTS (-SKI to -SKL), the enzyme targeted to peroxisomes. The possibility that soluble epoxide hydrolase-SKI was sorted slowly to peroxiosmes from the cytosol was examined by stably expressing rat soluble epoxide hydrolase-SKI appended to the green fluorescent protein. Green fluorescent protein soluble epoxide hydrolase-SKI was strictly cytosolic, indicating that -SKI was not a temporally inefficient putative type 1 PTS. Import of soluble epoxide hydrolase-SKI into peroxisomes in plant cells revealed that the context of -SKI on soluble epoxide hydrolase was targeting permissible. These results show that the C-terminal -SKI is a non-functional putative type 1 PTS on soluble epoxide hydrolase and suggest the existence of distinct cytosolic and peroxisomal targeting variants of soluble epoxide hydrolase in mouse and rat.

Suppression of cytochrome P450 Cyp2f2 mRNA levels in mice by the peroxisome proliferator diethylhexylphthalate

Exposure to peroxisome proliferators, which are extensively used, causes a number of pleiotrophic effects. Prolonged exposure to the peroxisome proliferator, DEHP, causes hepatic hyperplasia and liver tumors in rats and mice. This exposure can also induce a number of enzymes. To identify additional genes that are regulated by DEHP, mRNA differential display was used. One of the genes affected is cytochrome 450 Cyp2f2, a naphthalene hydroxylase. Using northern analysis, RNase protection assay, and RT-PCR, we show that the Cyp2f2 mRNA levels are decreased in mouse liver following DEHP treatment. A smaller Cyp2f2 mRNA transcript was also detected in kidney and these transcript levels were also suppressed but to a lesser extent than that in the liver. The response to DEHP in mouse liver is both dose and time dependent.

Chromosomal localisation, inducibility, tissue-specific expression and strain differences in three murine peroxisome-proliferator-activated-receptor genes

Three murine peroxisome-proliferator-activated-receptor (PPAR) genes were localised to chromosome 15 (PPAR alpha), chromosome 17 (PPAR beta) and chromosome 6 (PPAR gamma). The expression of the three PPAR RNAs was determined using a specific RNase protection assay. In liver RNA, PPAR alpha was expressed at the highest level, with 20-fold lower levels of PPAR beta, and very low levels of PPAR gamma. The three PPAR RNAs showed no sex-specific differences in expression, and the levels of these transcripts were unaffected by treatment of mice with testosterone or the potent peroxisome proliferator, methylclofenapate. In agreement with this data, the level of PPAR alpha protein in liver was unchanged after treatment of mice with methylclofenapate. Investigation of the tissue-specific distribution revealed that the PPAR alpha RNA was expressed at highest levels in liver, to moderate levels in kidney and brown adipose tissue, and at low levels elsewhere. PPAR beta was expressed at moderate levels in liver, and lower levels in other tissues, including brown adipose tissue. In contrast, PPAR gamma RNA was expressed at low levels in liver or epididymal white adipose tissue and at very low levels elsewhere, but was expressed at high levels in brown adipose tissue. The tissue distribution of these receptors suggests an important role in lipid metabolism and toxicity for individual members of the PPAR family. The expression of PPAR alpha and PPAR beta RNAs was examined in 13 strains of mice, and the levels of expression varied within a fourfold range. Polymorphism in the size of PPAR alpha RNA from Swiss-Webster mice was detected, and shown to be due to a 2-bp mutation in the 3' non-coding region of PPAR alpha in Swiss Webster mice.

Effects of prolonged administration of perfluorooctanoic acid on hepatic activities of enzymes which detoxify peroxide and xenobiotic in the rat

Male and female rats were fed a diet containing 0.01% (w/w) perfluorooctanoic acid (PFOA) for 2 or 26 weeks, and the effects on enzymes that participate in the metabolism of peroxides and xenobiotics in liver were studied. Elevated activity of peroxisomal beta-oxidation persisted throughout the treatment of male rats with PFOA for 26 weeks. The activity of glutathione (GSH) peroxidase towards hydrogen peroxide was depressed significantly by the prolonged administration. The long-term treatment of male rats with PFOA decreased the activity of GSH peroxidase towards cumene hydroperoxide and increased the activity of microsomal NADPH-dependent lipid peroxidation. The activities of GSH reductase and hepatic content of GSH remained unchanged. There was no difference in the content of conjugated dienes in microsomal lipid between male rats exposed to PFOA for 26 weeks and age-matched control. The activities of GSH S-transferase towards 1-chloro-2,4-dinitrobenzene and 1,2-dichloro-4-nitrobenzene were depressed by the short-term administration of PFOA to male rats, and this inhibition became pronounced during the prolonged treatment. Microsomal cytochrome P450 was induced by the short-term treatment of male rats with PFOA, and elevated levels persisted throughout the treatment for 26 weeks. Upon the administration of PFOA to male rats for 2 weeks, the activity of 7-ethoxycoumarin O-deethylase was increased markedly, whereas the activities of either aniline p-hydroxylase or aminopyrine N-demethylase were unchanged. Although an age-dependent decrease was observed in the activity of 7-ethoxycoumarin O-deethylase, the activity in male rats treated with PFOA for 26 weeks was higher than that of age-matched control, to the same extent as was observed with the short-term treatment. The prolonged administration of PFOA to male rats caused a significant increase in the activity of both aniline p-hydroxylase and aminopyrine N-demethylase. Little changes were found in the same parameters tested in female rats even after the prolonged administration of PFOA.

Biochemical characterization of a variant form of cytosolic epoxide hydrolase induced by parental exposure to N-ethyl-N-nitrosourea

1. ENU4 mice express a protein variant originally detected in a CBF1 mouse sired by a C57BL/6 mouse exposed to N-ethyl-N-nitrosourea. It appears to be an isoelectric point variant of cytosolic epoxide hydrolase. Affinity purified cytosolic epoxide hydrolase from ENU4 mice has a pI of approximately 5.1 compared to 5.6 in other mouse strains. 2. Clofibrate induced cytosolic epoxide hydrolase to similar levels in five strains of mice. However, CBF1 and ENU4 mice were more sensitive to the induction of palmitoyl CoA oxidase activity. 3. Except for isoelectric point, the physico- and immunochemical properties of cytosolic epoxide hydrolase from ENU4 mice were similar to those of the other mouse strains. Substrate specificities for five of six substrates tested were also similar.

Mouse strain differences in glutathione S-transferase activity and aflatoxin B1 biotransformation

Previous studies have suggested that mice are resistant to the carcinogenic effects of aflatoxin B1 (AFB1) and that this resistance is largely the result of expression of an isoenzyme of glutathione S-transferase (GST) with high activity toward AFB1-8,9-epoxide. Significant interstrain differences in cytosolic GST activities toward a variety of substrates have been reported in mice. If such differences exist for the conjugation of AFB1-8,9-epoxide, then there may be significant mouse strain differences in susceptibility to AFB1-induced hepatocarcinogenicity. The hepatic microsomal and cytosolic biotransformation of AFB1 was studied in 8 different strains of mice fed a purified diet. GST-mediated conjugation of AFB1-8,9-epoxide with glutathione and GST activity toward 1-chloro-2,4-dinitrobenzene (CDNB), 1,2-dichloro-4-nitrobenzene (DCNB), ethacrynic acid (ECA) and cumene hydroperoxide (CHP) were determined with cytosolic fractions from 8-10 pooled livers. Specific activities of cytochrome-P-450-mediated oxidation of AFB1 to aflatoxin Q1 (AFQ1), aflatoxin M1 (AFM1), and aflatoxin P1 (AFP1), as well as the reactive intermediate AFB1-8,9-epoxide, were determined with hepatic microsomal fractions from each mouse strain. No striking differences in specific activity between mouse strains were observed for any of the P-450- or GST-mediated enzymatic pathways measured, although some statistically significant differences were found. GST specific activities toward AFB1-8,9-epoxide, CDNB, DCNB, ECA and CHP ranged from 1.5-2.1, 2,830-5,370, 81-144, 38-69 and 32-73 nmol/mg protein/min, respectively. The rate of formation of AFB1-8,9-epoxide ranged from 208 to 465 pmol/mg protein/min. The specific activities of AFQ1,AFM1, and AFP1 formation by microsomes ranged from 36-70, 161-326, and 252-426 pmol/mg protein/min, respectively. Mice fed a standard rodent chow diet showed evidence of microsomal and cytosolic enzyme induction when compared to mice fed a purified diet. The lack of substantial differences in enzyme specific activities between mouse strains suggests that interstrain variations in the hepatocarcinogenic effects of AFB1 in mice should not be large.

Proliferation of peroxisomes and induction of cytosolic and microsomal epoxide hydrolases in different strains of mice and rats after dietary treatment with clofibrate

1. The effects of dietary clofibrate (0.5%, w/w, for 10 days) on seven inbred strains of mice--C57BL/6, C57BL/B10A(5R), ATL/OLA, C3H/HE/OLA, BALB/C, CBA/CA and A/J/OLA--and three strains of rats--Sprague-Dawley, Wistar and LOU/OLA--have been investigated. Liver weight, peroxisome proliferation, catalase activity, cytosolic, microsomal and mitochondrial epoxide hydrolase activities, cytochrome oxidase activity, microsomal cytochrome P-450 content and cytosolic glutathione transferase activity in liver were determined, together with cytosolic and microsomal epoxide hydrolase and cytosolic glutathione transferase activities in the kidneys. 2. In all cases peroxisome proliferation and induction of cytosolic epoxide hydrolase were observed in livers of rodents exposed to clofibrate. Thus, no non-responsive strains were found and further evidence for a coupling between these two phenomena was provided. In many cases significant increases in the liver microsomal cytochrome P-450 content and decreases in the hepatic cytosolic glutathione transferase activity were also seen. 3. High levels of cytosolic epoxide hydrolase were found in the rat kidney. In several strains of mice and rats renal cytosolic epoxide hydrolase activity was increased by clofibrate. 4. There were often considerable strain differences. However, in general mice had higher cytosolic epoxide hydrolase and glutathione transferase activities, whereas rats had higher microsomal epoxide hydrolase activities.

Effect of hypolipidemic compounds on lauric acid hydroxylation and phase II enzymes

Treatment of male Fischer 344 rats with various hypolipidemic drugs of different peroxisome proliferating potency (1-benzylimidazole, acetylsalicylic acid, clofibrate, tiadenol) led to an induction of liver lauric acid hydroxylase, whereas probucol, which is not a peroxisome proliferator, did not induce this enzyme. Activity of bilirubin UDP-glucuronosyltransferase was increased by all the compounds tested. The highest increase was observed after treatment with acetylsalicylic acid (2.3-fold). High correlation (r = 0.953) was observed between the activities of lauric acid hydroxylase and the corresponding activities of cytosolic epoxide hydrolase reported previously. The amount of microsomal epoxide hydrolase was not changed by any of the compounds. Whereas clofibrate and tiadenol decreased glutathione S-transferase activity with 1-chloro-2,4-dinitrobenzene as substrate, 1-benzylimidazole and probucol increased this activity. With 4-hydroxynonenal as a substrate qualitatively the same results were obtained with the exception that probucol did not affect the enzyme activity. When glutathione S-transferase activity was measured with cis-stilbene oxide as substrate only the more than five-fold increase after treatment with 1-benzylimidazole was significantly different from control values. Activity of dihydrodiol dehydrogenase was increased after treatment of rats with 1-benzylimidazole (1.5-fold), whereas application of tiadenol led to a decrease of enzyme activity. Feeding of male guinea pigs with clofibrate did not change the activity of peroxisomal beta-oxidation, cytosolic epoxide hydrolase or lauric acid hydroxylase. However, treatment with tiadenol caused an increase of these activities.

Hormonal regulation of the developmental pattern of epoxide hydrolases. Studies in rat liver

Hormonal influences on the developmental pattern of epoxide hydrolases (EH) were investigated in livers from male and female Fischer F-344 rats. During ontogeny, activities of rat liver microsomal and cytosolic epoxide hydrolases (cEH and mEH) increased gradually until puberty when activities in males rose rapidly to become 1.5-fold to 2.0-fold higher than those in females. These sex differences were not observed in the adult rat if males were castrated 24 hr after birth. In castrated males, as well as in females, testosterone propionate (TP, 0.5 mg s.c. in 50 microliters peanut oil) injected on days 1, 3 and 5 postpartum increased mEH and cEH activities at adulthood compared to peanut oil-treated controls. In another study to determine effects on adults of neonatal exposure to a prototype-inducing agent, phenobarbital (PB, 30 mg/kg s.c., qd, in 0.9% saline) was injected in male and female neonates on days 1 through 5 postpartum. Although no long-term effect on mEH activities appeared on days 28, 45 and 60, hepatic mEH activities increased in all treatment groups on days 90 and 120. Collectively, these studies indicate that neonatal exposure to testosterone and PB alters the developmental pattern of EH activities, including final adult levels. Thus, full adult expression of these activities depends on hormonal influences exerted neonatally.