The use of 2,4,5,2',4',5'-hexachlorobiphenyl (6-CB) as an unmetabolizable lipophilic model compound

Association of occupational exposure to pesticides with overweight in farmers in Southern Brazil

INTRODUCTION

Exposure to pesticides may be related to overweight and associated comorbidities. The aim of this work was to evaluate occupational exposure to pesticides, overweight and associated comorbidities among farmers in Southern Brazil.

METHODS

This cross-sectional study included a random sample of 257 farmers, living in the municipality of Mafra and Planalto, southern Brazil. Data on pesticide use and overweight prevalence from farmers were collected using an in-person interview questionnaire, followed by blood collection and biochemical analyses.

RESULTS

Pesticide exposure was positively correlated with body mass index, waist circumference, waist-to-hip ratio, triglycerides and glucose levels, presence of hypertension and metabolic syndrome. Besides that, the fact of being exposed to pesticides represents a decrease of no protein thiol groups. Furthermore, the main pesticides used by farmers have hepatic toxicity.

CONCLUSION

These findings suggest that exposure to pesticides may be associated with overweight and associated comorbidities. Further studies are required to validate our findings and elucidate the specific mechanisms by which these pollutants contribute to the development of overweight.

Editor's Highlight: Transplacental and Lactational Transfer of Firemaster® 550 Components in Dosed Wistar Rats

Firemaster® 550 (FM 550) is a commercial mixture of organophosphate and brominated flame retardants currently in use as a replacement for pentaBDE. Its organophosphate components include triphenyl phosphate (TPHP) and a suite of isopropylated triarylphosphate isomers (ITPs); its brominated components include 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB) and bis (2-ethylhexyl)-2,3,4,5-tetrabromophthalate (BEH-TEBP). Taken together, these chemicals have been shown to be endocrine disrupting and potentially toxic, and human exposure to them is widespread. In this study, maternal transfer of FM 550 components, and in some cases their metabolites, was investigated in dosed Wistar rats. Gestational and lactational transfer were examined separately, with dams orally exposed to 300 or 1000 µg of FM 550 for 10 consecutive days during gestation (gestational day [GD] 9-18) or lactation (postnatal day [PND] 3-12). Levels of parent compounds were measured in fetus and whole pup tissue homogenates, and in dam and pup serum, and several metabolites were measured in dam and pup urine. EH-TBB body burdens resulting from lactational transfer were approximately 200- to 300-fold higher than those resulting from placental transfer, whereas low levels of BEH-TEBP were transferred during both lactation and gestation. TPHP and ITPs were rapidly metabolized by the dams and were not detected in whole tissue homogenates. However, diphenyl phosphate (DPHP) and mono-isopropylphenyl phenyl phosphate (ip-PPP) were detected in urine from the dosed animals. This study is the first to confirm ip-PPP as a urinary metabolite of ITPs and establish a pharmacokinetic profile of FM 550 in a mammalian model.

KEY WORDS

Firemaster 550 ;: lactational transfer ;: gestational transfer; metabolites; rodent.

Macronutrient composition determines accumulation of persistent organic pollutants from dietary exposure in adipose tissue of mice

Accumulation of persistent organic pollutants (POPs) has been linked to adipose tissue expansion. As different nutrients modulate adipose tissue development, we investigated the influence of dietary composition on POP accumulation, obesity development and related disorders. Lifespan was determined in mice fed fish-oil-based high fat diets during a long-term feeding trial and accumulation of POPs was measured after 3, 6 and 18months of feeding. Further, we performed dose-response experiments using four abundant POPs found in marine sources, PCB-153, PCB-138, PCB-118 and pp'-DDE as single congeners or as mixtures in combination with different diets: one low fat diet and two high fat diets with different protein:sucrose ratios. We measured accumulation of POPs in adipose tissue and liver and determined obesity development, glucose tolerance, insulin sensitivity and hepatic expression of genes involved in metabolism of xenobiotics. Compared with mice fed diets with a low protein:sucrose ratio, mice fed diets with a high protein:sucrose ratio had significantly lower total burden of POPs in adipose tissue, were protected from obesity development and exhibited enhanced hepatic expression of genes involved in metabolism and elimination of xenobiotics. Exposure to POPs, either as single compounds or mixtures, had no effect on obesity development, glucose tolerance or insulin sensitivity. In conclusion, this study demonstrates that the dietary composition of macronutrients profoundly modulates POP accumulation in adipose tissues adding an additional parameter to be included in future studies. Our results indicate that alterations in macronutrient composition might be an additional route for reducing total body burden of POPs.

Fruit and vegetable intake, as reflected by serum carotenoid concentrations, predicts reduced probability of polychlorinated biphenyl-associated risk for type 2 diabetes: National Health and Nutrition Examination Survey 2003-2004

Type 2 diabetes has been shown to occur in response to environmental and genetic influences, among them nutrition; food intake patterns; sedentary lifestyle; body mass index; and exposure to persistent organic pollutants, such as polychlorinated biphenyls (PCBs). Nutrition is essential in the prevention and management of type 2 diabetes and has been shown to modulate the toxicity of PCBs. Serum carotenoid concentrations, considered a reliable biomarker of fruit and vegetable intake, are associated with the reduced probability of chronic diseases, such as type 2 diabetes and cardiovascular disease. Our hypothesis is that fruit and vegetable intake, reflected by serum carotenoid concentrations, is associated with the reduced probability of developing type 2 diabetes in US adults with elevated serum concentrations of PCBs 118, 126, and 153. This cross-sectional study used the Center for Disease Control and Prevention database, National Health and Nutrition Examination Survey 2003-2004, in logistic regression analyses. Overall prevalence of type 2 diabetes was approximately 11.6% depending on the specific PCB. All 3 PCBs were positively associated with the probability of type 2 diabetes. For participants at higher PCB percentiles (eg, 75th and 90th) for PCB 118 and 126, increasing serum carotenoid concentrations were associated with a smaller probability of type 2 diabetes. Fruit and vegetable intake, as reflected by serum carotenoid concentrations, predicted notably reduced probability of dioxin-like PCB-associated risk for type 2 diabetes.

Sustained expression of CYPs and DNA adduct accumulation with continuous exposure to PCB126 and PCB153 through a new delivery method: Polymeric implants

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Polymeric implants successfully achieved continuous exposure to PCBs in rats.

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PCB126 resulted in significant oxidative DNA damage (8-oxodG) in rat liver and lung.

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PCB126 or in combination with PCB153 induced PON1 and its activity in the liver.

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The induction was even greater for PON3 and AhR gene transcription.

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Co-treatment reduced mammary PCB153 and increased liver PCB126 and PCB153 levels.

A new delivery method via polymeric implants was used for continuous exposure to PCBs. Female Sprague-Dawley rats received subcutaneous polymeric implants containing PCB126 (0.15% load), PCB153 (5% load), or both, for up to 45 d and release kinetics and tissue distribution were measured. PCB153 tissue levels on day 15 were readily detected in lung, liver, mammary and serum, with highest levels in the mammary tissue. PCB126 was detected only in liver and mammary tissues. However, a completely different pharmacokinetics was observed on co-exposure of PCB153 and PCB126, with a 1.8-fold higher levels of PCB153 in the liver whereas a 1.7-fold lower levels in the mammary tissue. PCB126 and PCB153 caused an increase in expression of key PCB-inducible enzymes, CYP 1A1/2 and 2B1/2, respectively. Serum and liver activities of the antioxidant enzymes, PON1 and PON3, and AhR transcription were also significantly increased by PCB126. ³²P-postlabeling for polar and lipophilic DNA-adducts showed significant quantitative differences: PCB126 increased 8-oxodG, an oxidative DNA lesion, in liver and lung tissues. Adduct levels in the liver remained upregulated up to 45 d, while some lung DNA adducts declined. This is the first demonstration that continuous low-dose exposure to PCBs via implants can produce sustained tissue levels leading to the accumulation of DNA-adducts in target tissue and induction of indicator enzymes. Collectively, these data demonstrate that this exposure model is a promising tool for long-term exposure studies.

Measuring in vitro biotransformation rates of super hydrophobic chemicals in rat liver s9 fractions using thin-film sorbent-phase dosing

Methods for rapid and cost-effective assessment of the biotransformation potential of very hydrophobic and potentially bioaccumulative chemicals in mammals are urgently needed for the ongoing global evaluation of the environmental behavior of commercial chemicals. We developed and tested a novel solvent-free, thin-film sorbent-phase in vitro dosing system to measure the in vitro biotransformation rates of very hydrophobic chemicals in male Sprague-Dawley rat liver S9 homogenates and compared the rates to those measured by conventional solvent-delivery dosing. The thin-film sorbent-phase dosing system using ethylene vinyl acetate coated vials was developed to eliminate the incomplete dissolution of very hydrophobic substances in largely aqueous liver homogenates, to determine biotransformation rates at low substrate concentrations, to measure the unbound fraction of substrate in solution, and to simplify chemical analysis by avoiding the difficult extraction of test chemicals from complex biological matrices. Biotransformation rates using sorbent-phase dosing were 2-fold greater than those measured using solvent-delivery dosing. Unbound concentrations of very hydrophobic test chemicals were found to decline with increasing S9 and protein concentrations, causing measured biotransformation rates to be independent of S9 or protein concentrations. The results emphasize the importance of specifying both protein content and unbound substrate fraction in the measurement and reporting of in vitro biotransformation rates of very hydrophobic substances, which can be achieved in a thin-film sorbent-phase dosing system.

Inhibition of the promotion of hepatocarcinogenesis by 2,2',4,4',5,5'-hexachlorobiphenyl (PCB-153) by the deletion of the p50 subunit of NF-kappa B in mice

Polychlorinated biphenyls (PCBs) are persistent and ubiquitous environmental chemicals that bioaccumulate and have hepatic tumor promoting activity in rodents. The present study examined the effect of deleting the p50 subunit of NF-kappaB on the hepatic tumor promoting activity of 2,2',4,4',5,5'-hexachlorobiphenyl (PCB-153) in mice. Both wild-type and p50-/- male mice were injected i.p. with diethylnitrosamine (DEN, 90 mg/kg) and then subsequently injected biweekly with 20 i.p. injections of PCB-153 (300 micromol/kg/injection). p50 deletion decreased the tumor incidence in both PCB- and vehicle-treated mice, whereas PCB-153 slightly (P=0.09) increased the tumor incidence in wild-type and p50-/- mice. PCB-153 increased the total tumor volume in both wild-type and p50-/- mice, but the total tumor volume was not affected by p50 deletion in either PCB- or vehicle-treated mice. The volume of tumors that were positive for glutamine synthetase (GS), which is indicative of mutations in the beta-catenin gene, was increased in both wild-type and p50-/- mice administered PCB-153 compared to vehicle controls, and inhibited in p50-/- mice compared to wild-type mice (in both PCB- and vehicle-treated mice). The volume of tumors that were negative for GS was increased in p50-/- mice compared to wild-type mice but was not affected by PCB-153. PCB-153 increased cell proliferation in normal hepatocytes in wild-type but not p50-/- mice; this increase was inhibited in p50-/- mice. In hepatic tumors, the rate of cell proliferation was much higher than in normal hepatocytes, but was not affected by PCB treatment or p50 deletion. The rate of apoptosis, as measured by the TUNEL assay, was not affected by PCB-153 or p50 deletion in normal hepatocytes. In hepatic tumors, the rate of apoptosis was lower than in normal hepatocytes; PCB-153 slightly (P=0.10) increased apoptosis in p50-/- but not wild-type mice; p50 deletion had no effect. Taken together, these data indicate that the absence of the NF-kappaB p50 subunit inhibits the promoting activity of PCB-153 and alters the proliferative and apoptotic changes in mouse liver in the response to PCBs.

Perinatal co-exposure to methylmercury and PCB153 or PCB126 in rats alters the cerebral cholinergic muscarinic receptors at weaning and puberty

In the last few decades, combined exposure to methylmercury (MeHg) and polychlorinated biphenyls (PCBs) from fish and seafood, and their potentially interactive effects on neurodevelopment, have been giving increasing cause for concern. We examined the combined effects of MeHg and either a non-dioxin PCB (PCB153) or a dioxin-like PCB (PCB126) congener on the developing brain cholinergic muscarinic receptors (MRs). These receptors are known to play a major role in many central functions including higher cognitive processes and the modulation of extrapyramidal motor activity. MRs in pup rat brains diminished following prenatal and lactational exposure, from gestational day [GD]7 to postnatal day [PND]21, to MeHg (0.5mg/kgbodyweight[bw]/day), PCB153 (5mg/kgbw/day), and PCB126 (100ng/kg/day), alone or in combination. Total MR density, as well as M1, M2, and M3 receptor subtypes of the weanling and pubertal rats, were affected in a brain-area-, gender-, time- and compound-dependent fashion. MeHg decreased (by 15-20%) the total MR density in a delayed (PND36) manner in the cerebral cortex of both genders, and early (at weaning) in the cerebellum of both genders, with the effect lasting until puberty (in males only). MeHg decreased the ACh M1- and M3-immunopositive neurons in the cerebral cortex and also increased the M2-immunopositive Bergmann glia in the cerebellum. PCB153 also induced a delayed (PND36) decrease (of 20%) in total MR number in the cerebellum of the male offspring and in the cerebral cortex of both genders. The latter effect was coupled with a decrease in ACh M1- and ACh M3-immunopositive neuron populations. PCB126 decreased (by 30-40%) total MR density in a gender-dependent manner, males being more sensitive than females. The effect was evident early (at PND21) and lasted until puberty in the cerebellum, while it was observed later (at PND36) in the cerebral cortex. The M1 and M3 receptors were similarly affected by PCB126. Co-exposure to MeHg and either PCB153 or PCB126 had the same effect on the cerebral MRs as exposure to each compound alone. The results rule out additive or synergistic interactions between MeHg and PCB153 or PCB126 on MRs in the brain areas examined. Some early-onset changes persisted until puberty, while other modifications became manifest only at the advanced time point (PND36), when the brain levels of total Hg, PCB153, and PCB126 had declined. These data support the ability of MeHg and PCBs to induce delayed neurotoxicity after developmental exposure.

Plasma concentration of organochlorine compounds is associated with age and not obesity

It has been suggested that obese individuals, because of an increased dilution space (body fat) for lipophilic organochlorines compounds, may have greater levels of toxic pollutants than lean sedentary individuals. It is important to further examine this possibility because of the potential contribution of organochlorine pesticides in the development of Parkinson's disease and other neurological diseases. The aim of this study was to further investigate the relationship between the magnitude of obesity and the plasma concentration of organochlorines for a wide range of BMI (with participants at steady state body weight). Fifty-three individuals were selected on the basis of their body mass index (BMI): lean controls (n=16; mean BMI 22.8+/-2.2 kg/m(2); mean age 38.8+/-9.4 years), obese individuals (n=19; mean BMI 33.4+/-3.0 kg/m(2); mean age 38.6+/-7.6 years) and morbidly obese individuals (n=18; mean BMI 49.3+/-6.5 kg/m(2); mean age 44.3+/-9.2 years). Blood samples were analyzed for organochlorine compounds. The relationship between the total plasma organochlorine concentration and BMI was tested using a multiple regression analysis. Age was included in the model. There was no relationship between the total plasma organochlorine concentration and BMI. Organochlorine concentrations, however, were correlated with age (BMI-adjusted R(2)=0.46; p<0.001). At steady state body weight, toxic pollutant concentrations are not associated to obesity but strongly correlate with age.

Antagonistic effects of methyl-mercury and PCB153 on PC12 cells after a combined and simultaneous exposure

The study of interactions for those substances which tend to accumulate in food and affect the nervous system appears to be a fundamental point to characterize the combined exposure in vitro. In this study we included two food contaminants which are known neurotoxicants: methyl-mercury (Me-Hg) and the ortho-substituted PCB 153. PC12 cells were treated with Me-Hg (range 1e-7, 2e-6 M) and PCB153 (range 1e-5, 4e-4 M) in single and combined synchronous experiments and a mathematical model was set up according to the Loewe additivity criterion to evaluate the level of interaction between toxicants, using viability as end-point. At some concentrations (Me-Hg 5e-7 M and PCB153 1e-4 and 2e-4 M; Me-Hg 1e-6M and PCB153 5e-5 M; Me-Hg 1e-7 M and PCB153 4e-4 M), a statistically significant antagonist effect was observed. No interaction was observed for other combinations. The analysis of other toxicological parameters known to be modified in single exposure experiments (TBARS and intra-cellular dopamine) confirmed the viability results. The results of our work represent a starting point to generate novel information on the interactions between PCB153 and Me-Hg in vitro, as well as a new relevant experimental and mathematical approach useful to investigate the effects of different toxicant mixtures.

Kinetic assessment of persistent halogenated xenobiotics in cell culture models: comparison of mono- and poly-halogenated compounds

We evaluated the suitability of single and multiple cell type cultures as model systems to characterise cellular kinetics of highly lipophilic compounds with potential ecotoxicological impact. Confluent mono-layers of human skin fibroblasts, rat astrocytoma C6 cells, non-differentiated and differentiated mouse 3T3 cells were kept in culture medium supplemented with 10% foetal calf serum. For competitive uptake experiments up to four different cell types, grown on glass sectors, were exposed for 3h to (14)C-labelled model compounds, dissolved either in organic solvents or incorporated into unilamellar lecithin liposomes. Bromo-, or chloro-benzenes, decabromodiphenylether (DBP), and dichlorodiphenyl ethylene (DDE) were tested in rather high concentration of 20 microM. Cellular toxicity was low. Compound levels were related to protein, DNA, and triglyceride contents. Cellular uptake was fast and dependent on physico-chemical properties of the compounds (lipophilicity, molecular size), formulation, and cell type. Mono-halogenated benzenes showed low and similar uptake levels (=low accumulation compounds). DBP and DDE showed much higher cellular accumulations (=high accumulation compounds) except for DBP in 3T3 cells. Uptake from liposomal formulations was mostly higher than if compounds were dissolved in organic solvents. The extent of uptake correlated with the cellular content of triglycerides, except for DBP. Uptake competition between different cell types was studied in a sectorial multi-cell culture model. For low accumulation compounds negligible differences were found among C6 cells and fibroblasts. Uptake of DDE was slightly and that of DBP highly increased in fibroblasts. Well-defined cell culture systems, especially the sectorial model, are appropriate to screen for bioaccumulation and cytotoxicity of (unknown) chemical entities in vitro.

Levels of PCB 126 and PCB 153 in plasma and tissues in goats exposed during gestation and lactation

The aim of the present study was to gain knowledge about the disposition of the PCB congeners 126 and 153 in a goat model where pregnant does were given oral doses of PCB from day 60 of gestation until delivery. The goat kids were thus exposed to PCB during gestation and lactation. The doses of PCB 153 and PCB 126 were 98 and 49 ng/kg body wt/day, respectively. PCB levels were measured in plasma from the does at day 90 of gestation and at delivery, and in plasma from the kids at birth and four weeks post partum. Concentrations of PCB were analysed in brain, liver and fat tissue from the does six weeks after delivery and in liver and fat tissue from the kids at nine months of age. The ratio of estimated body burden to ingested dose in the does, was 0.95 +/- 0.07 for PCB 153 and 0.41 +/- 0.03 for PCB 126. Approximately 9% of PCB 153 and 6% of PCB 126 was transferred from the mothers to their kids during gestation and lactation. Prenatal exposure contributed to a much lower fraction of the body burden than postnatal PCB intake via milk, due to the fact that almost 100% of the PCB 153 transferred from the does to kids was transferred via milk, and the PCB 126 intake via milk was threefold higher than the calculated body burden. The hepatic PCB 126 concentration in both does and kids was significantly higher than the concentration in fat, in contrast to PCB 153, where the highest concentrations were found in fat. A significant difference in body burden between the does at delivery, the newborn kids, and the kids at four weeks of age, did not influence the plasma concentration of PCB 153 on a fat weight basis, which showed no difference with sampling time. Our results suggest that PCB 126 and PCB 153 have different pharmacokinetic properties. The higher levels of PCB 126 in liver tissue compared to fat tissue confirm the concept of hepatic sequestration. The similar blood concentration of PCB 153 in the does at delivery and their newborn kids despite the considerable difference in body burden, suggests a high degree of placental transfer. This supports previous observations that low molecular weight, lipid-soluble, non-polar chemicals reach the fetus to the greatest possible extent. For PCB 153, the body burden may provide the appropriate dose metric at steady state, but may give a minor underestimation of PCB 126 at low environmental exposure levels due to hepatic sequestration.

Biotransformation rates of Ugilec 141 (tetrachlorobenzyltoluenes) in rat and trout microsomes

In vitro biotransformation rates of tetrachlorobenzyltoluene (TCBT) isomers 3,3',4,4'-Cl4-2-Me (TCBT 87), 3,3',4,4'-Cl4-5-Me (TCBT 88), and 3,3',4',5-Cl4-4-Me (TCBT 94) were determined using trout and rat hepatic microsomes. The disappearance of the TCBTs from the in vitro system followed first-order kinetics. The estimated biotransformation constants (k) for the rat ranged from 0.96 to 4.14 h(-1). Biotransformation rates for trout microsomes were much lower and ranged from 0.009 to 0.017 h(-1).

Intake, fecal excretion, and body burden of polychlorinated dibenzo-p-dioxins and dibenzofurans in breast-fed and formula-fed infants

To assess toxicokinetics of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), oral intake and fecal excretion were measured in two breast-fed infants and one formula-fed infant during the 1st y of life. The intake of these compounds was up to 50 times higher in the breast-fed infants. In these children, fecal excretion of the main tetra- to hexachlorinated congeners was less than 9% of the intake at age of 1 and 5 mo, indicating almost complete intestinal absorption during breast-feeding. In contrast, distinctly higher fecal excretion rates were observed for the hepta- and octachlorinated compounds. Despite much lower PCDD/PCDF intake after weaning, concentrations in stool fat did not decrease substantially. We conclude that concentrations in fecal fat more or less reflect those in body fat. Additionally, PCDD/PCDF concentrations were measured in blood fat of all infants (and in a second formula-fed baby) at the age of 11 mo. International toxicity equivalent (I-TEq) concentrations in the formula-fed infants were less than 25% of maternal values and about 10 times lower than in the infants breast-fed for 6-7 mo. In the latter, a distinct accumulation was found for the tetra- to hexachlorinated congeners compared with maternal concentrations. We conclude that accumulation of PCDDs and PCDFs in infants is as high as expected on the basis of intake data and assuming complete absorption and negligible elimination during the 1st y of life.