Transport and cellular uptake of polychlorinated biphenyls (PCBs)--II. Changes in vivo in plasma lipoproteins and proteins of pigeons in response to PCBs, and a proposed model for the transport and cellular uptake of PCBs

Ontogeny of plasma proteins, albumin and binding of diazepam, cyclosporine, and deltamethrin

BACKGROUND

To characterize the ontogeny of plasma albumin and total proteins, due to the lack of a comprehensive pediatric database. Secondly, to establish the magnitude and duration of maturational changes in binding of highly-bound drugs/chemicals.

METHODS

Anonymized plasma samples from 296 donors were pooled in 6 age brackets from birth to adolescence. Total protein and albumin levels were measured in each age group, as was the age-dependency of plasma binding of diazepam (DZP), cyclosporine (CYC), and deltamethrin (DLM), a pyrethroid insecticide.

RESULTS

Plasma levels of albumin and total proteins steadily increased for the first 1-3 y of life. Unbound DZP and CYC fractions were elevated three- to fourfold in neonates, but decreased to adult levels after 1 and 3 y, respectively. Unbound DLM levels exceeded those in adults for just 1 mo.

CONCLUSION

Neonates and infants under 1-3 y may be at risk from increased amounts of free drug, when given standard doses of some highly-bound drugs. Pyrethroid insecticides might be anticipated to pose increased risk for 1 mo.

Whole genome transcript profiling of drug induced steatosis in rats reveals a gene signature predictive of outcome

Drug induced steatosis (DIS) is characterised by excess triglyceride accumulation in the form of lipid droplets (LD) in liver cells. To explore mechanisms underlying DIS we interrogated the publically available microarray data from the Japanese Toxicogenomics Project (TGP) to study comprehensively whole genome gene expression changes in the liver of treated rats. For this purpose a total of 17 and 12 drugs which are diverse in molecular structure and mode of action were considered based on their ability to cause either steatosis or phospholipidosis, respectively, while 7 drugs served as negative controls. In our efforts we focused on 200 genes which are considered to be mechanistically relevant in the process of lipid droplet biogenesis in hepatocytes as recently published (Sahini and Borlak, 2014). Based on mechanistic considerations we identified 19 genes which displayed dose dependent responses while 10 genes showed time dependency. Importantly, the present study defined 9 genes (ANGPTL4, FABP7, FADS1, FGF21, GOT1, LDLR, GK, STAT3, and PKLR) as signature genes to predict DIS. Moreover, cross tabulation revealed 9 genes to be regulated ≥10 times amongst the various conditions and included genes linked to glucose metabolism, lipid transport and lipogenesis as well as signalling events. Additionally, a comparison between drugs causing phospholipidosis and/or steatosis revealed 26 genes to be regulated in common including 4 signature genes to predict DIS (PKLR, GK, FABP7 and FADS1). Furthermore, a comparison between in vivo single dose (3, 6, 9 and 24 h) and findings from rat hepatocyte studies (2 h, 8 h, 24 h) identified 10 genes which are regulated in common and contained 2 DIS signature genes (FABP7, FGF21). Altogether, our studies provide comprehensive information on mechanistically linked gene expression changes of a range of drugs causing steatosis and phospholipidosis and encourage the screening of DIS signature genes at the preclinical stage.

Dietary antioxidants (selenium and N-acetylcysteine) modulate paraoxonase 1 (PON1) in PCB 126-exposed rats

Environmental pollutants polychlorinated biphenyls (PCBs), especially dioxin-like PCBs, cause oxidative stress and associated toxic effects, including cancer and possibly atherosclerosis. We previously reported that PCB 126, the most potent dioxin-like PCB congener, not only decreases antioxidants such as hepatic selenium (Se), Se-dependent glutathione peroxidase, and glutathione (GSH) but also increases levels of the antiatherosclerosis enzyme paraoxonase 1 (PON1) in liver and serum. To probe the interconnection of these three antioxidant systems, Se, GSH, and PON1, we examined the influence of varying levels of dietary Se and N-acetylcysteine (NAC), a scavenger of reactive oxygen species (ROS) and precursor for GSH synthesis, on PON1 in the absence and presence of PCB 126 exposure. Male Sprague-Dawley rats, fed diets with differing Se levels (0.02, 0.2, or 2 ppm) or NAC (1%), were treated with a single intraperitoneal injection of corn oil or various doses of PCB 126 and euthanized 2 weeks later. PCB 126 significantly increased liver PON1 mRNA, protein level and activity, and serum PON1 activity in all dietary groups but did not consistently increase thiobarbituric acid levels (thiobarbituric acid reactive substances, TBARS), an indicator of lipid oxidation and oxidative stress, in liver or serum. Inadequate (high or low) dietary Se decreased baseline and PCB 126-induced aryl hydrocarbon receptor (AhR) expression but further increased PCB 126-induced cytochrome P450 1A1 (CYP1A1) expression, the enzyme believed to be the cause for PCB 126-induced oxidative stress. In addition, a significant inverse relationship was observed not only between dietary Se levels and PON1 mRNA and PON1 activity but also with TBARS levels in the liver, suggesting significant antioxidant protection from dietary Se. NAC lowered serum baseline TBARS levels in controls and increased serum PON1 activity but lowered liver PON1 activities in animals treated with 1 μmol/kg PCB 126, suggesting antioxidant activity by NAC primarily in serum. These results also show an unexpected predominantly inverse relationship between Se or NAC and PON1 during control and PCB 126 exposure conditions. These interactions should be further explored in the development of dietary protection regimens.

Exposure to the three structurally different PCB congeners (PCB 118, 153, and 126) results in decreased protein expression and altered steroidogenesis in the human adrenocortical carcinoma cell line H295R

Polychlorinated biphenyls (PCB), synthetic, persistent organic pollutants (POP), are detected ubiquitously, in water, soil, air, and sediments, as well as in animals and humans. PCB are associated with range of adverse health effects, such as interference with the immune system and nervous system, reproductive abnormalities, fetotoxicity, carcinogenicity, and endocrine disruption. Our objective was to determine the effects of three structurally different PCB congeners, PCB118, PCB 126, and PCB 153, each at two concentrations, on the steroidogenic capacity and proteome of human adrenocortical carcinoma cell line cultures (H295R) . After 48 h of exposure, cell viability was monitored and estradiol, testosterone, cortisol and progesterone secretion measured to quantify steroidogenic capacity of the cells. Two-dimensional (2D) gel-based proteomics was used to screen for proteome alterations in H295R cells in response to the PCB. Exposure to PCB 118 increased estradiol and cortisol secretion, while exposure to PCB 153 elevated estradiol secretion. PCB 126 was the most potent congener, increasing estradiol, cortisol, and progesterone secretion in exposed H295R cells. Seventy-three of the 711 spots analyzed showed a significant difference in normalized spot volumes between controls (vehicle only) and at least one exposure group. Fourteen of these protein spots were identified by liquid chromatography with mass spectroscopy (LC-MS/MS). Exposure to three PCB congeners with different chemical structure perturbed steroidogenesis and protein expression in the H295R in vitro model. This study represents an initial analysis of the effects on proteins and hormones in the H295R cell model, and additional studies are required in order to obtain a more complete understanding of the pathways disturbed by PCB congeners in H295R cells. Overall, alterations in protein regulation and steroid hormone synthesis suggest that exposure to PCB disturbs several cellular processes, including protein synthesis, stress response, and apoptosis.

Hepatic cytochrome P450 activity and pollutant concentrations in paradise shelducks and southern black-backed gulls in the South Island of New Zealand

Cytochrome P450 (CYP) enzymes catalyse the oxidative metabolism of various xenobiotics including environmental pollutants. We investigated liver microsomal CYP marker activities in 60 paradise shelducks (Tadorna variegata; herbivore) and 77 southern black-backed gulls (Larus dominicanus; omnivore) collected at three sites with putatively different levels of pollution in the South Island of New Zealand. Ethoxyresorufin O-deethylase (EROD) activity was high in birds at an urban landfill site compared to those at a relatively pristine and an agricultural site. Analysis of p-nitrophenol hydroxylase and erythromycin demethylase activities indicated the presence of two additional CYP isoforms in shelducks but no additional form in gulls. Total polychlorinated biphenyl (PCB) concentrations (ranges: shelducks, 0.073-6.2; gulls, 8.2-330 ng/g wet weight) were high in landfill samples suggesting a link to EROD induction and, in landfill shelducks, EROD was independently associated with Hg and Pb concentration. PCB congener-specific assessments indicated the metabolism of at least two congeners (#28 and #74) is induced in shelducks. DDE concentrations (ranges: shelducks, 0.85-320; gulls, 44-4800 ng/g) were high in birds at the landfill and agricultural sites. Body weight tended to be lower in landfill birds, but whether this reflects the greater energetic demands of pollutant detoxification remains to be investigated.

Cellular uptake of lipoproteins and persistent organic compounds--an update and new data

There are a number of interactions related to the transport of lipophilic xenobiotic compounds in the blood stream of mammals. This paper will focus on the interactions between lipoproteins and persistent organic pollutants (POPs) and how these particles are taken up by cells. A number of POPs including the pesticide p,p'-dichlorodiphenyltrichloroethane (DDT), and especially its metabolite p,p'-dichlorodiphenyldichloroethene (DDE), interacts with nuclear hormone receptors causing these to malfunction, which in turn results in a range of deleterious health effects in humans. The aim of the present study was to determine the role of lipoprotein receptors in mouse embryonic fibroblast (MEF) cells in conjunction with uptake of DDT-lipoprotein complexes from supplemented media in vitro. Uptake of DDT by MEF cells was investigated using MEF1 cells carrying the receptors low-density lipoprotein receptor-related protein (LRP) and low-density lipoprotein receptor (LDLR) present and MEF4 cells with no LRP and LDLR expression. Cells were incubated together with the complex of low-density lipoproteins (LDL) and [(14)C]DDT. The receptor function was further evaluated by adding the 40kDa receptor-associated protein (RAP) which blocks receptor activity. The results showed that [(14)C]DDT uptake was decreasing when the LDL concentration was increasing. There was no strong evidence for a receptor-mediated uptake of the [(14)C]DDT-lipoprotein complex. To conclude, DDT travels in the blood stream and can cross cell membranes while being transported as a DDT-lipoprotein complex. The lipoproteins do not need receptors to cross cell membranes since passive diffusion constitutes a major passageway.

From mother to child: investigation of prenatal and postnatal exposure to persistent bioaccumulating toxicants using breast milk and placenta biomonitoring

The exposure levels of placenta and paired breast milk samples to selected organochlorine compounds and pesticides from Danish and Finnish samples have been investigated. p,p'-DDE is the dominant pollutant, beta-HCH, hexachlorobenzene, endosulfan-I, dieldrin, oxychlordane, cis-heptachlor epoxide and p,p'-DDT being the other major constituents. Their concentrations are linearly correlated between milk and placenta in similar patterns for Danish and Finnish samples. Milk samples have higher levels of these pollutants than placenta on lipid base. However, the apparently not correlated compounds, such as alpha-HCH, pentachlorobenzene, pentachloroanisole and methoxychlor, are generally accumulated more in placenta, which may suggest a tissue specific metabolic activity. Thus, depending on the compound of interest, biomonitoring may be done in placenta only or in both matrices.

Comparative evaluation of hepatotoxic and nephrotoxic effects of aroclors 1221 and 1254 in female rats

Polychlorinated biphenyls (PCBs) are persistent environmental pollutants. This study compared effects of two PCB mixtures, Aroclors 1221 (A1221) and 1254 (A1254) on serum levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), urea, creatinine and uric acid in female rats. Histopathological changes in the liver and kidney were also examined. A group of adult Wistar rats served as controls. Groups II and III were subcutaneously injected with A1221 and A1254 at 10 mg/kg every other day for 6 weeks. At the end of this period, all animals were decapitated and blood samples were collected. Serum urea, creatinine, uric acid, ALT, AST and ALP levels were determined. Liver and kidney were collected for histopathological examination. They were fixed in formaldehyde and processed for light microscopy. Both A1221 and 1254 significantly elevated serum ALT (p < 0.05) and AST (p < 0.01) levels compared to the control group. Serum ALP values were significantly increased by A1221 (p < 0.05), but they were unaffected in the A1254 group. Treatment with both A1221 and A1254 significantly increased serum levels of urea (p < 0.05), creatinine (p < 0.01) and uric acid (except in the A1221 group; p < 0.005). Distinct histopathological changes including renal corpuscular atrophy, peritubular vascular congestion and dilated cortical tubules, sinusoidal dilatation, congestion and mononuclear cell infiltration were observed. These findings suggest that PCBs may cause nephrotoxicity and hepatotoxicity in female rats.

Fatty acids, lipids, and cytochrome p-450 monooxygenase in hepatic microsomes of minks fed fish-based diets and exposed to Aroclor 1242

Minks were fed different fish-based diets and exposed to 1 mg/d of the commercial polychlorinated biphenyl (PCB) mixture Aroclor 1242 for 4 wk (November-December 1995) or 21 wk (July-December 1998). In all the dietary groups, the PCBs increased hepatic phospholipid (PL) content. No significant increase was detected in hepatic triacylglycerols (TGs). In the minks fed the different fish diets, the PCBs caused qualitatively and quantitatively different changes in the microsomal fatty acids. In the minks that were fed a diet rich in fat and low in polyunsaturated fatty acids (PUFAs), the PCBs increased the percentage of oleic acid (18:1n-9, characteristic of the storage TGs) at the expense of n-3 PUFAs. This seemed to be due to inclusions of TGs in the membrane fragments and partly due to incorporation of TG-derived fatty acids into the membrane PLs. In addition, significant decrease of PUFAs was detected also in the hepatic TGs. The concomitant decrease in the concentrations of hepatic vitamin E suggested that lipid oxidation may also contribute to the decrease of the PUFAs. In the liver of the minks fed a low-fat but PUFA- and vitamin E-rich diet, the fatty acid changes due to the PCBs (the 21-wk exposure) remained small but the cytochrome P-450 system was significantly activated. In the minks fed Baltic herring (rich in organochlorines via the foodweb), the cytosolic glutathione S-transferase (GST) activity, levels of microsomal thiobarbituric acid-reactive substances (TBARS), and hepatic PLs were significantly elevated. In conclusion, in the mink the microsomal fatty acid changes were not directly connected with the ethoxyresorufin O-deethylase (EROD) activity or P-450 expression. Apparently, the PCBs produced definite fatty acid changes only in certain lipid matrices of tissue. In addition, a rich dietary supply of PUFAs and vitamin E may prevent these changes, even in a long-term subchronic exposure.

Environmental pollutants as aetiological agents in female reproductive pathology: placental glycan expression in normal and polychlorinated biphenyl (PCB)-exposed mink (Mustela vison)

Polychlorinated biphenyls (PCB) may cause growth retardation or fetal death in mink. Pathological changes in endotheliochorial mink placentae were examined following exposure to PCB during gestation. Placentae from six animals with average fetal crown-rump (C-R) lengths between 16 and 53 mm given 0.65 mg/day Clophen A50 (low dose), and one from five animals with an average fetal C-R length of 14 mm given 1.3 mg/day (high dose), were examined. Mink were treated from 9 to 24 days before mating until killed at day 53. Placentae were formalin-fixed with four size-matched controls and embedded in resin. Sections were stained with five biotinylated lectins to detect specific glycans. Both control and treated (low dose) mink showed degenerative changes in maternal endothelium from 13-16 mm, revealed by increased lectin binding, caused probably by high cell turnover during tissue remodelling. Controls of 47 and 50 mm exhibited fewer degenerate maternal endothelial cells. The 31-mm PCB-treated tissue showed separation of the trophoblast from the interstitial layer and, at 53 mm, loss of its normal architecture, increased damage to maternal endothelium and infarction. High-dose PCB was extremely toxic, producing fetal death or extensive placental infarction by 14 mm C-R length. Lectin staining thus revealed the effects of PCB toxicity, shown by increased injury to maternal endothelium and severe trophoblastic damage.

Long-term effects of Aroclor 1254 (PCBs) on plasma lipid and carnitine concentrations in rhesus monkey

Sixty-seven female rhesus monkeys (Macaca mulatta) were orally dosed daily for 152 weeks with 0, 5, 20, 40, and 80 micrograms Aroclor 1254 (PCB)/kg body wt. Blood polychlorinated biphenyl (PCB) concentrations were highly positively correlated (r = 0.92, P < 0.001) with doses of PCB administered. A comprehensive analysis of plasma lipids/lipoproteins revealed a PCB-associated increase in plasma triglycerides and decreases in plasma total cholesterol, high-density lipoprotein cholesterol (HDL-chol), very-low plus low-density lipoprotein cholesterol (VLDL+LDL-chol), and total carnitine (which is involved in fatty acid metabolism). All of the lipid/lipoprotein changes were significantly (P < or = 0.05) correlated with blood PCB concentration. These data, obtained after 152 weeks of continuous daily exposure of a primate model to PCB support a causal relationship between plasma lipid changes and PCB intake. Previously, causality has been refuted on the premise that the commonly observed elevation of triglycerides with increasing concentration of blood PCB is a reflection, not of PCB dose, but of the partitioning of PCB between tissues (adipose) and blood in proportion to the blood lipid present. The mechanism of the plasma lipid changes was not investigated in this study but the altered lipid/lipoprotein pattern is discussed with respect to known cardiovascular risk profiles.

Changes in plasma lipoprotein metabolism in chicks in response to polychlorinated biphenyls (PCBs)

The results of the present study strongly suggest that the hypertriglyceridaemia in chicks treated with Aroclor 1254 is a result of reduction in VLDL clearance rather than an increase in rate of VLDL secretion. The decrease in post-heparin LPL activity responsible for reduced VLDL clearance may be mediated by cytokines produced by chronic activation of the immune system.

Distribution and elimination in vivo of polychlorinated biphenyl (PCB) isomers and congeners in the pigeon

1. Pigeons were injected with a single dose of commercial PCB mixtures (Aroclor 1248 plus Aroclor 1260), killed 120 h later and the abundance of individual PCBs was determined in adipose tissue, gonads, liver, brain, kidney, heart, muscle and blood. 2. Elimination factors for individual PCBs were calculated. Values of greater than 1 were obtained for PCBs with meta-para-unsubstituted carbon atoms in at least one ring, indicating that elimination exceeded accumulation in all or most tissues. By contrast, ortho-meta unsubstituted PCBs had elimination factors less than 1, thus indicating their impaired removal. 3. Tissues with high microsomal monooxygenase activity had the highest elimination factors for individual PCBs (i.e. liver greater than kidney greater than muscle greater than heart). 4. Distribution of individual PCBs was independent of sex and of ortho-chlorine substitution and showed that 90% of total PCBs in cadavers was present in adipose tissue, 2% in kidneys, 1% each in brain, muscle and heart and less than 0.1% in blood. 5. The distribution of the highly toxic non-ortho and mono-ortho substituted PCBs did not differ amongst all tissues analysed. 6. The present studies indicate that elimination of PCBs in vivo is favoured by the molecular feature of unsubstituted meta-para carbon atoms in the biphenyl moiety.