Differential effect of peroxisome proliferators on rat glutathione S-transferase isoenzymes

Genetic polymorphisms of PPAR genes and human cancers: evidence for gene-environment interactions

Peroxisome proliferator-activated receptors (PPARs) are nuclear transcription factors that play a role in lipid metabolism, cell proliferation, terminal differentiation, apoptosis, and inflammation. Although several cancer models have been suggested to explain PPARs' involvement in tumorigenesis, however, their role is still unclear. In this review, we examined associations of the different PPARs, polymorphisms and various types of cancer with a focus on gene-environment interactions. Reviewed evidence suggests that functional genetic variants of the different PPARs may modulate the relationship between environmental exposure and cancer risk. In addition, this report unveils the scarcity of reliable quantitative environmental exposure data when examining these interactions, and the current gaps in studying gene-environment interactions in many types of cancer, particularly colorectal, prostate, and bladder cancers.

The Impact of Di(2-ethylhexyl)phthalate on Cancer Progression

Di(2-ethylhexyl)phthalate (DEHP), a widely used plasticizer, mainly serves as an additive to render polyvinyl chloride (PVC) soft and flexible. PVC plastics have become ubiquitous in our modern society. Yet, the leaching of DEHP from PVC-based consumables ultimately results in the deposition in certain tissues via inadvertent applications. Health risks for human populations exposed to DEHP has been assumed by studies on rodents and other species, including the DEHP-induced developmental dysregulation, reproductive impairments, tumorigenesis, and diseases in a transgenerational manner. In this review, we comprehensively summarize the accumulated literature regarding the multifaceted roles of DEHP in the activation of the nuclear receptors, the alteration of the redox homeostasis, epigenetic modifications and the acquisition of chemoresistance.

Peroxisome proliferator-activated receptor alpha target genes

The peroxisome proliferator-activated receptor alpha (PPARα) is a ligand-activated transcription factor involved in the regulation of a variety of processes, ranging from inflammation and immunity to nutrient metabolism and energy homeostasis. PPARα serves as a molecular target for hypolipidemic fibrates drugs which bind the receptor with high affinity. Furthermore, PPARα binds and is activated by numerous fatty acids and fatty acid-derived compounds. PPARα governs biological processes by altering the expression of a large number of target genes. Accordingly, the specific role of PPARα is directly related to the biological function of its target genes. Here, we present an overview of the involvement of PPARα in lipid metabolism and other pathways through a detailed analysis of the different known or putative PPARα target genes. The emphasis is on gene regulation by PPARα in liver although many of the results likely apply to other organs and tissues as well.

Vitamin C and resveratrol supplementation to rat dams treated with di(2-ethylhexyl)phthalate: impact on reproductive and oxidative stress end points in male offspring

This study was carried out to assess the influence of di(2-ethylhexyl)phthalate (DEHP) alone or associated with antioxidants on the male reproductive system in newborn rats, emphasizing the implications of oxidative stress and hormonal balance during prenatal and early postnatal periods. Wistar females were exposed by oral route to DEHP alone or associated with antioxidants from gestational day 7 to lactational day 2 according to the following treatment regimens: (C) vehicle control (canola oil + 1% Tween-80); (V) vitamin C (200 mg/kg) + canola oil; (R) resveratrol (10 mg/kg) + canola oil; (D) DEHP (500 mg/kg) + 1% Tween-80; (DV) DEHP (500 mg/kg) + vitamin C (200 mg/kg); and (DR) DEHP (500 mg/kg) + resveratrol (10 mg/kg). Two male pups per litter were randomly selected and necropsied on postnatal day 2. The brain and liver were removed and weighed and anogenital distance (AGD) was measured. Additionally, the testes were removed for assessment of intratesticular testosterone levels and histopathology; the liver was used to measure biomarkers of oxidative stress. Vitamin C and resveratrol alone did not affect the reproductive end points and did not induce oxidative stress. Exposure of dams to DEHP alone and associated with antioxidants resulted in hepatomegaly in offspring and significantly increased the incidence of multinucleated gonocytes in seminiferous cords. Testosterone and AGD presented a trend to decrease in DEHP-exposed groups. Catalase activity increased only in groups exposed to DEHP associated with antioxidants, although GST (gluthatione-S-transferase) activity decreased in all DEHP-exposed groups. The levels of hydroperoxides increased only in group exposed to DEHP associated with vitamin C. These results indicate that the association of DEHP with antioxidants was unable to ameliorate DEHP-induced reproductive changes, and the coadministration of DEHP and these antioxidants might even contribute to an overall increase in oxidative stress.

Use of di(2-ethylhexyl)phthalate-containing infusion systems increases the risk for cholestasis

INTRODUCTION

Most polyvinylchloride infusion systems are plasticized with up to 60% of di(2-ethylhexyl)phthalate (DEHP). DEHP is easily extracted from the tubing by total parenteral nutrition (TPN) solutions and has been shown to have toxic effects on various organ systems including the liver in animals and humans. A role was postulated for DEHP in the development of hepatobiliary dysfunction in premature and newborn infants receiving parenteral nutrition, and the incidence of cholestasis was investigated after changing from polyvinylchloride infusion systems to polyvinylchloride-free infusion systems.

MATERIALS AND METHODS

Two 3-year periods from 1998 to 2004 were investigated retrospectively before and after changing from polyvinylchloride to polyvinylchloride-free infusion systems in our department. This resulted in 1 group of 30 patients treated with polyvinylchloride lines and a second group of 46 patients treated with polyvinylchloride-free lines. The 2 groups were examined for the incidence of cholestasis and other possible contributing factors. Statistics were performed by using SAS software (SAS Institute, Cary, NC).

RESULTS

After changing infusion systems, the incidence of cholestasis dropped from 50% to 13%. Using DEHP-plasticized polyvinylchloride infusion systems for TPN increased the risk for cholestasis by a factor of 5.6. The use of polyvinylchloride lines correlated strongly with the development of TPN-associated cholestasis (P = .0004).

CONCLUSIONS

Using DEHP-containing polyvinylchloride infusions systems contributes to the development of cholestasis. Therefore, the use of DEHP-free infusion systems for TPN is recommended, especially in premature and newborn infants.

Role of Oxidative Stress in Peroxisome Proliferator-Mediated Carcinogenesis

In this review, the evidence about the role of oxidative stress in the induction of hepatocellular carcinomas by peroxisome proliferators is examined. The activation of PPAR-alpha by peroxisome proliferators in rats and mice may produce oxidative stress, due to the induction of enzymes like fatty acyl coenzyme A (CoA) oxidase (AOX) and cytochrome P-450 4A1. The effect of peroxisome proliferators on the antioxidant defense system is reviewed, as is the effect on endpoints resulting from oxidative stress that may be important in carcinogenesis, such as lipid peroxidation, oxidative DNA damage, and transcription factor activation. Peroxisome proliferators clearly inhibit several enzymes in the antioxidant defense system, but studies examining effects on lipid peroxidation and oxidative DNA damage are conflicting. There is a profound species difference in the induction of hepatocellular carcinomas by peroxisome proliferators, with rats and mice being sensitive, whereas species such as nonhuman primates and guinea pigs are not susceptible to the effects of peroxisome proliferators. The possible role of oxidative stress in these species differences is also reviewed. Overall, peroxisome proliferators produce changes in oxidative stress, but whether these changes are important in the carcinogenic process is not clear at this time.

Extraction of diethylhexylphthalate by home total parenteral nutrition from polyvinyl chloride infusion lines commonly used in the home

OBJECTIVES

Recently, our group detected that polyvinyl chloride (PVC) perfusion lines leach large amounts of the toxic plasticizer diethylhexylphthalate (DEHP) under conditions typical of intensive care units. In the present study, we investigated the extraction of DEHP from PVC connecting tubes that are commonly used for total parenteral nutrition (TPN) solutions. The aim of the study was to estimate the amount of DEHP to which children receiving home TPN are exposed for months and years.

MATERIALS AND METHODS

1000 mL of TPN, identical in constitution and amount to the home TPN of 1 of our patients, were perfused through 5 different connecting tube systems and collected in hexane-rinsed glass bottles. The concentration of DEHP in the TPN was analyzed before and after perfusion.

RESULTS

Before perfusion of the lines, the solution had a DEHP concentration of 0.05 to 0.69 microg/mL (baseline value). After perfusion of the lines, the load of DEHP in the solution varied between 1.41 and 2.07 microg/mL. This TPN was established for children weighing 20 kg. The daily dosage is between 71 and 104 microg x kg(-1) x day(-1). TPN is administered at home for many months and years. The monthly charge of DEHP is between 42.3 and 62.1 mg. Children weighing 20 kg therefore receive a dosage between 2.1 and 3.1 mg x kg(-1) x month(-1).

CONCLUSIONS

Diethylhexylphthalate and its metabolite monoethylhexylphthalate have been demonstrated to be carcinogenic, embryotoxic, hepatotoxic, pneumotoxic, and cardiotoxic and are known to disrupt endocrine pathways and liver detoxifying capacity in animals. They are suspected of having multiple effects in humans as well. The doses presented above should therefore be avoided in children receiving home TPN by the use of tubing systems that are completely free of DEHP. Such systems are available.

Extraction of the plasticizers diethylhexylphthalate and polyadipate from polyvinylchloride nasogastric tubes through gastric juice and feeding solution

OBJECTIVES

Except for polyadipate, which is used as an alternative in polyvinylchloride (PVC) feeding tubes, diethylhexylphthalate (DEHP) is the plasticizer used almost exclusively in PVC medical products. A clear response to the chronic intake of DEHP has been shown in several organ systems from different species. In the present study, we compared the extraction of DEHP and polyadipate from PVC gastric tubes.

METHODS

An in vivo setting was simulated. We used 5 cm of PVC nasogastric tubes containing DEHP or polyadipate, which were incubated with gastric juice for 1 week and a feeding solution for 4 weeks. The leakage of these plasticizers was measured daily in the gastric juice group and weekly in the feeding solution group. The amount of plasticizer extracted was compared between groups and days.

RESULTS

In the feeding solution group, the extraction of DEHP ranged from 200 to 542 microg after 1 week and from 660 to 1700 microg after 4 weeks. The extraction of polyadipate was 10 times lower than that of DEHP. In the gastric juice group, extracted DEHP ranged from 635 to 1043 microg, whereas the extraction of polyadipate was 100 times lower.

CONCLUSIONS

Within 1 week, the extraction of DEHP from a 5-cm PVC tube reaches up to 1 mg. Extrapolated, this represents an in vivo load of up to 4 mg. The load accumulated by a newborn in an intensive care unit can therefore easily reach several milligrams of DEHP per day. Polyadipate nasogastric tubes may therefore be an alternative and help to reduce the daily load of DEHP.

Extraction of di-ethylhexyl-phthalate from perfusion lines of various material, length and brand by lipid emulsions

BACKGROUND

The plasticizer di-ethylhexyl-phthalate (DEHP) is extracted especially by lipid emulsions from polyvinylchloride infusion systems. The aim of this study was to systematically examine the extraction from perfusion lines commonly used in our hospital for lipid emulsion infusions.

METHODS

Perfusion lines made from polyvinylchloride of various lengths and brands, polyethylene, polyvinylchloride/polyethylene (PVC/PE) and polyvinylchloride/polyurethane (PVC/PU), were perfused with lipid emulsions according to the circumstances of newborns on an intensive care unit, i.e. high temperature, 24-hour duration and low quantities. Concentration of di-ethylhexyl-phthalate was determined with gas chromatograph mass spectrometry.

RESULTS

The lipid emulsions before perfusion had a contamination with DEHP of 0.82 microg/ml. Pure PVC lines of 1.5 m length leached between 74 microg/ml and 107 microg/ml. Sterilization of the lines did not influence DEHP extraction. After perfusion of DEHP-free PVC lines and PVC-free lines, the emulsions had a contamination with DEHP of 0.23 microg/ml and 0.11 microg/ml, respectively. PVC/PU co-extruded lines leached 73 microg/ml. PVC/PE lines leached 41.6 microg/ml.

CONCLUSIONS

Lipid emulsions contain a production-inherent load of DEHP. Perfusion through PVC-perfusion lines extracts a varying large amount of DEHP depending on length and brand of the perfusion lines. Co-extruded PVC/PU and PVC/PE lines, intended to avoid DEHP contamination, leach a similar amount of DEHP and thus do not avoid the DEHP toxicity issue. The load accumulated by a baby on an intensive care unit easily reaches several milligrams of DEHP per day. As its effect upon biologic systems has been proven, and alternatives (PE or PU perfusion lines) are available, PVC and PVC co-extruded perfusion lines should be abandoned for infusions, especially in babies.

Protein profiling of mouse livers with peroxisome proliferator-activated receptor alpha activation

Peroxisome proliferator-activated receptor alpha (PPARalpha) is important in the induction of cell-specific pleiotropic responses, including the development of liver tumors, when it is chronically activated by structurally diverse synthetic ligands such as Wy-14,643 or by unmetabolized endogenous ligands resulting from the disruption of the gene encoding acyl coenzyme A (CoA) oxidase (AOX). Alterations in gene expression patterns in livers with PPARalpha activation were delineated by using a proteomic approach to analyze liver proteins of Wy-14,643-treated and AOX(-/-) mice. We identified 46 differentially expressed proteins in mouse livers with PPARalpha activation. Up-regulated proteins, including acetyl-CoA acetyltransferase, farnesyl pyrophosphate synthase, and carnitine O-octanoyltransferase, are involved in fatty acid metabolism, whereas down-regulated proteins, including ketohexokinase, formiminotransferase-cyclodeaminase, fructose-bisphosphatase aldolase B, sarcosine dehydrogenase, and cysteine sulfinic acid decarboxylase, are involved in carbohydrate and amino acid metabolism. Among stress response and xenobiotic metabolism proteins, selenium-binding protein 2 and catalase showed a dramatic approximately 18-fold decrease in expression and a modest approximately 6-fold increase in expression, respectively. In addition, glycine N-methyltransferase, pyrophosphate phosphohydrolase, and protein phosphatase 1D were down-regulated with PPARalpha activation. These observations establish proteomic profiles reflecting a common and predictable pattern of differential protein expression in livers with PPARalpha activation. We conclude that livers with PPARalpha activation are transcriptionally geared towards fatty acid combustion.

Comparison of oxidative stress and changes of xenobiotic metabolizing enzymes induced by phthalates in rats

Phthalates are widely used as a plasticizer and cause a peroxisome proliferation. Peroxisome proliferators (PPs), such as di-2-ethylhexyl phthalate (DEHP) and clofibrate (CF) are known to have a hepatocarcinogenic potential in rodents. It has been proposed that these PPs may cause hepatocellular cancer by an oxidative damage-mediated mechanism(s). The primary purpose of this study is to find whether there is a difference between the oxidative damage by hepatocarcinogenic PPs (DEHP and CF) and the oxidative damage by weak PPs [di-n-butyl phthalate (DBP) and n-butylbenzyl phthalate (BBP)]. The second purpose is to investigate if phthalates can affect the phase I/phase II enzymes, and if the effect of PPs on metabolizing enzymes correlates with peroxisome proliferation or not. After rats were treated with PPs (DEHP, DBP and BBP; 50, 200, 1000 mg/kg, CF; 100 mg/kg, p.o., for 14 days), the activities of metabolizing enzymes and peroxisomal enzymes were investigated, and the oxidative damage was measured using 8-hydroxydeoxyguanosine (8-OHdG) in the DNA and malonedialdehyde (MDA) in the livers. These four PPs significantly increased the relative liver weights, palmitoyl-CoA oxidation and activity of carnitine acetyltransferase. DEHP was found to be the most potent PP among three phthalates. A dramatic and dose-dependent increase in hepatic MDA levels was observed in CF (100 mg/kg), DEHP (>or=50 mg/kg), DBP and BBP (>or=200 mg/kg) groups. However, the 8-OHdG in hepatic DNA was increased only in DEHP (1000 mg/kg) and CF groups. Activities of cytochrome p4501A1, 1A2, 3A4, UDP-glucuronosyl transferase and glutathione S-transferase were decreased overall by PPs, but there is no correlation between the inhibitory effect on metabolizing enzymes and the peroxisome proliferation. These results indicate that 8-OHdG positively correlates with carcinogenic potential of PPs, but other factors as well as peroxisomal H(2)O(2) could be involved in the generation of 8-OHdG and the carcinogenesis of PPs. The present findings also demonstrate that the effect of PPs on xenobiotic metabolizing enzymes may be independent of the peroxisome proliferation and the oxidative stress. Thus it is possible that the PPs affect the hepatic toxification/detoxification capacity even in humans.

Profiling of acyl-CoA oxidase-deficient and peroxisome proliferator Wy14,643-treated mouse liver protein by surface-enhanced laser desorption/ionization ProteinChip Biology System

Peroxisome proliferators induce hepatic peroxisome proliferation and hepatocellular carcinomas in rodents. These chemicals increase the expression of the peroxisomal beta-oxidation pathway and the cytochrome P-450 4A family, which metabolizes lipids, including fatty acids. Mice lacking fatty acyl-CoA oxidase (AOX-/-), the first enzyme of the peroxisomal beta-oxidation system, exhibit extensive microvesicular steatohepatitis, leading to hepatocellular regeneration and massive peroxisome proliferation. To investigate proteins involved in peroxisome proliferation, we adopted a novel surface-enhanced laser desorption/ionization (SELDI) ProteinChip technology to compare the protein profiles of control (wild-type), AOX-/-, and wild-type mice treated with peroxisome proliferator, Wy-14,643. The results indicated that the protein profiles of AOX-/- mice were similar to the wild-type mice treated with Wy14,643, but significantly different from the nontreated wild-type mice. Using four different ProteinChip Arrays, a total of 40 protein peaks showed more than twofold changes. Among these differentially expressed peaks, a downregulated peak was identified as the major urinary protein in both AOX-/- and Wyl4,643-treated mice by SELDI. The identification of MUP was further confirmed by two-dimensional electrophoresis and liquid chromatography coupled tandem mass spectrometry (LC-MS-MS). This SELDI method offers several technical advantages for detection of differentially expressed proteins, including ease and speed of screening, no need for chromatographic processing, and small sample size.

Peroxisome proliferators increase the formation of BPDE-DNA adducts in isolated rat hepatocytes

Peroxisome proliferators are known to modulate the activity of xenobiotic-metabolising enzymes, including glutathione S-transferase (GST) and cytochrome P-450 (CYP). In this study the effect of peroxisome proliferators silvex and di(2-ethylhexyl)phthalate (DEHP) on the formation of (+)-anti-benzo(a)pyrene -7,8-dihydrodiol-9,10-epoxide (BPDE)-DNA adducts from a proximate mutagen and carcinogen (-)-transbenzo(a)pyrene-7,8-dihydrodiol (BPDD) has been investigated. Rat CYP1A1 metabolises BPDD to mutagenic BPDE, which may form DNA adducts or, alternatively, be detoxified by hydrolysis or glutathione conjugation. In this experiment the formation of BPDE-DNA adducts was significantly increased in hepatocytes isolated from all silvex treated rats and two out of four DEHP treated rats (14 day treatment). The activity of CYP1A1 was increased whereas GST was reduced by the peroxisome proliferator silvex. These changes were more significant than those induced by DEHP. We have hypothesised that the formation of BPDE-DNA adducts was primarily due to the increased BPDD activation to BPDE versus reduced detoxication of BPDE. Other hepatic changes induced by the peroxisome proliferators, e.g. peroxisome proliferation per se and increased mitotic activity of the liver could have an effect on the outcome of BPDD exposure.

Peroxisome proliferator nafenopin potentiated cytotoxicity and genotoxicity of cyclophosphamide in the liver and bone marrow cells

Peroxisome proliferators are ubiquitous rodent hepatocarcinogens, known to modulate the activities of xenobiotic-metabolising enzymes such as glutathione S-transferases (GST) and mixed-function oxidase (cytochrome P-450). In addition these compounds induce pleiotropic changes in the liver of rodents even after a short-term treatment. It has been hypothesised that the enzymatic and cellular changes induced by peroxisome proliferators may alter the toxicity of other compounds activated by cytochrome P-450 and detoxified by GST isoenzymes. The effect of nafenopin-induced changes in the liver of rats on the toxicity of an anti-cancer drug cyclophosphamide was studied using cyto- and geno-toxicity parameters in the liver and bone marrow cells. The administration of cyclophosphamide (10 or 20 mg/kg bw) to the rats pre-treated with 80 mg/kg bw of nafenopin for 2 days resulted in significantly increased cytotoxic response in bone marrow cells. However, genotoxicity of cyclophosphamide was increased only in the liver of nafenopin pre-treated rats. Low level of genotoxicity in bone marrow could be accounted for potentiated cytotoxicity of cyclophosphamide. These events coincided with a significant, up to 5-fold, increase in indirect activation-detoxication index for cyclophosphamide, determined as a ratio of ECOD and GST activities, in nafenopin treated rats. This resulted from the induction of ECOD responsible for the formation of reactive metabolites of cyclophosphamide and reduced activity of GST responsible for their detoxication. In addition, mitotic activity of hepatocytes was increased in nafenopin treated rats that might also have an impact on the genotoxicity of cyclophosphamide in this organ.