Uptake of persistent environmental chemicals by cultured human cells

New emerging polybromobiphenyls in serum of general population and their disruption on thyroid hormone receptor β1

After the PBBs pollution incident in Michigan, a large number of studies focused on the exposure of people to 2,2',4,4',5,5'-hexabromobiphenyl (BB-153), but paid less attention to other PBBs congeners in human serum. In this study, three monobromobiphenyls (BB-1, BB-2 and BB-3), five dibromobiphenyls (BB-4, BB-7, BB-9, BB-10 and BB-15), decabromobiphenyl (BB-209) and BB-153 in the serum of the general population in Wuxi from 2012 to 2016 were detected by GC-MS/MS. The most abundant congeners in serum samples were BB-1(median 254 ng·g-1 lw), BB-10 (median 141 ng·g-1 lw) and BB-209 (median 68.4 ng·g-1 lw). The detection rate of BB-153 is less than 10%, and the concentration is far lower than that in other areas. The concentrations of BB-1, BB-10 and BB-209 are 3-4 orders of magnitude higher than the maximum concentration of BB-153. Serum concentrations of BB-209 increased significantly from 2012 to 2016 (p = 0.025). In addition, the concentrations of BB-1 in serum of females were significantly higher than that of males, and the concentrations of BB-1, BB-10 and BB-209 in serum of young adults were significantly higher than that of middle-aged adults. Finally, we found that BB-1 and BB-10 may have similar disruption on the binding of T3 and TRβ1 as BB-153, while BB-209 has little effect on the binding of T3 and TRβ1. This suggests that we should pay more attention to the damage of BB-1 and BB-10 to thyroid in the future.

Response of human non-small-cell lung cancer cells to the influence of Wogonin with SGK1 dynamics

A number of significant studies in the field of cell biology have revealed another pattern of intracellular signal transduction in which cells transmit information through the dynamics of key signaling molecules. Dynamical properties of p53 have been demonstrated to be the key factor in dictating cell fate, including cell cycle arrest, permanent cell cycle arrest, and cell death. Previous studies showed a negative feedback regulation pathway between SGK1 and p53, but the dynamics of SGK1 have never been reported before. Therefore, we used different dosing strategies of Wogonin to affect SGK1 dynamics and investigate its impact on cell response. Key factors, such as APAF1, BAX, GADD45A, p21, PML, and YPEL3, which are related to cell cycle arrest, senescence, and apoptosis, were measured at different time points after incubation with Wogonin. Western blot and quantitative reverse transcriptase-polymerase chain reaction analysis were used to examine protein and mRNA expression of these genes. In addition, we also used β-galactosidase staining and flow cytometric analysis to further verify the results. It was found that Wogonin inhibited cell viability and downregulated SGK1 protein levels; 20 μM Wogonin could induce non-small-cell lung cancer A549 cells into cell cycle arrest/senescence/apoptosis after 0.5/2/4 h, respectively; and SGK1 dynamics showed significant differences under different cell responses. Together, our findings showed that SGK1 protein dynamics can be an important part of intracellular signaling, directly influencing cellular response decisions.

PCB 136 atropselectively alters morphometric and functional parameters of neuronal connectivity in cultured rat hippocampal neurons via ryanodine receptor-dependent mechanisms

We recently demonstrated that polychlorinated biphenyl (PCB) congeners with multiple ortho chlorine substitutions sensitize ryanodine receptors (RyRs), and this activity promotes Ca²⁺-dependent dendritic growth in cultured neurons. Many ortho-substituted congeners display axial chirality, and we previously reported that the chiral congener PCB 136 (2,2',3,3',6,6'-hexachlorobiphenyl) atropselectively sensitizes RyRs. Here, we test the hypothesis that PCB 136 atropisomers differentially alter dendritic growth and other parameters of neuronal connectivity influenced by RyR activity. (-)-PCB 136, which potently sensitizes RyRs, enhances dendritic growth in primary cultures of rat hippocampal neurons, whereas (+)-PCB 136, which lacks RyR activity, has no effect on dendritic growth. The dendrite-promoting activity of (-)-PCB 136 is observed at concentrations ranging from 0.1 to 100 nM and is blocked by pharmacologic RyR antagonism. Neither atropisomer alters axonal growth or cell viability. Quantification of PCB 136 atropisomers in hippocampal cultures indicates that atropselective effects on dendritic growth are not due to differential partitioning of atropisomers into cultured cells. Imaging of hippocampal neurons loaded with Ca²⁺-sensitive dye demonstrates that (-)-PCB 136 but not (+)-PCB 136 increases the frequency of spontaneous Ca²⁺ oscillations. Similarly, (-)-PCB 136 but not (+)-PCB 136 increases the activity of hippocampal neurons plated on microelectrode arrays. These data support the hypothesis that atropselective effects on RyR activity translate into atropselective effects of PCB 136 atropisomers on neuronal connectivity, and suggest that the variable atropisomeric enrichment of chiral PCBs observed in the human population may be a significant determinant of individual susceptibility for adverse neurodevelopmental outcomes following PCB exposure.

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.

Effect of an environmentally relevant metabolized organochlorine mixture on porcine cumulus–oocyte complexes

Organochlorine compounds and their metabolites bioaccumulate and have been detected in follicular and genital tract fluids of humans and animals. This study was designed to investigate the effect of a metabolised organochlorine mixture, extracted from plasma of sows treated with an environmentally relevant organochlorine mixture in the course of a previous study, on porcine cumulus-oocyte complexes (COCs) in vitro. The major component of the metabolised mixture is 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene (p,p'-DDE) at 15.1 mg/l, which accounts for 40.7% of the total extract. Polychlorinated biphenyls (PCBs) account for 30.8% of the extract and hydroxylated PCB metabolites (OH-PCBs) for 11.8%. Exposure of COCs to the metabolised mixture induced a decrease of apoptotic cumulus cells at low concentrations and an increase at higher concentrations following a U-shaped curve (p=0.0106), with the intermediate treatment (3.6 microg/l OH-PCBs) significantly reducing apoptosis compared to the extraction control (p=0.05). However, the metabolised mixture did not affect cumulus expansion, oocyte maturation, penetration, development to blastocyst, or the number of cells per blastocyst. This study also indicates that organochlorine metabolites similar in concentrations to levels found in Arctic populations can affect growing cumulus-oocyte complexes without inducing an overt toxicological response.

Comparison of polychlorinated biphenyl (PCB) induced effects on innate immune functions in harbour and grey seals

Polychlorinated biphenyls (PCBs) are known to have detrimental effects on the innate immune system of several mammalian species. Top predators such as marine mammals may be badly affected as PCBs can bioaccumulate in their blubber to high concentrations and previous studies have suggested that harbour seals may be particularly vulnerable to the immunotoxic effects of such contaminants. To investigate the effects of PCBs on innate immune functions in phocid seals, blood samples were collected from harbour and grey seals and exposed in vitro to a mixture of Aroclors. Separated mononuclear (PBMCs) and polymorphonuclear (PMNCs) leukocytes from each species were incubated with Aroclors (at 3 and 30 ngml(-1)) for 3 and 24 h incubation periods, after which phagocytosis, respiratory burst and cytotoxic activity were measured. The phagocytic activity of harbour seal PMNCs was decreased at both incubation times and at both Aroclor concentrations tested, but there was no effect on the grey seals. Similarly, the respiratory burst activity of harbour seals was decreased at both incubation times, but only at the higher concentration used. There were no differences in the cytotoxic activity of the PBMCs with respect to incubation times or concentrations in either species. However, differences were observed in the level of cytotoxic activity against YAC-1 target cells, with the grey seal PBMCs showing higher levels of activity. The observed differences in phagocytosis, respiratory burst and cytotoxic activity of the leukocytes following incubation with PCBs may have implications for the previously recorded differences in disease susceptibility between grey and harbour seals.

Polychlorinated biphenyls are not substrates for the multidrug resistance transporter-1

The multidrug resistance (MDR) transporter is a phosphorylated glycoprotein (P-gp) that has been implicated in the efflux of a large variety of xenobiotics, thereby protecting vital organs. This study examines the hypothesis that the multidrug resistance transporter is involved in restricting the entry of polychlorinated biphenyls (PCBs) into the brain. Three test systems were used. First, the ATPase activity of the human P-gp was measured as an indicator of the interaction of PCBs with the MDR transporter. PCB congeners and metabolites included in the study were PCB 153, PCB 169, PCB 77, and the 4-hydroxy and 4,4'-dihydroxy metabolites of PCB 77. An increase in ATPase activity was observed for all the PCBs tested except the 4-hydroxy metabolite of PCB 77. Second, we studied the transport of (14)C-PCB 77 and (14)C-PCB153 in a cell-culture model using porcine kidney cells expressing the human MDR1 or the mouse mdr1a gene and compared it to the transport in control cells. No difference in directional transport due to P-gp was observed with either of the congeners in any of the cell lines. Finally, the distribution pattern of (14)C-PCB 77 in mdr1a knockout mice and genetically matched wild-type mice was measured. No significant differences in tissue distribution, especially in the brain tissue, were observed between wild-type and mdr1a knockout mice. These results suggest that some PCB congeners can bind to the MDR1 transporter; however, they may not be transported by it.

Hepatic vectorial transport of xenobiotics

The vectorial transport of xenobiotics across the hepatocyte is mediated by various transport and transfer proteins that differ in ligand specificity and function. The influx of xenobiotics from the blood across the sinusoidal membrane of the hepatocyte can occur through passive or active transport processes. Once in the cell, xenobiotics can be sequestered by intracellular transfer proteins that prevent refluxing of the chemical back through the sinusoidal membrane. Transfer proteins may also facilitate the localization of the xenobiotics within the cell to sites of metabolism (i.e., the endoplasmic reticulum) or elimination (i.e., the canalicular membrane). Intracellular transfer proteins include glutathione S-transferases, fatty acid-binding proteins, and 3 alpha-hydroxysteroid dehydrogenase. Intracellular nuclear transfer proteins have also been identified that facilitate the transfer of chemical carcinogens from the cytoplasm into the cell nucleus. Several active transport proteins exist on the canalicular membrane of the hepatocyte that mediate the efflux of chemicals from the cell into the biliary canaliculus. Xenobiotic efflux proteins include the multispecific organic anion transporter, that eliminates xenobiotics that have undergone conjugation with glutathione, glucuronic acid, and possibly sulfate; and, P-glycoprotein, an active transporter that actively effluxes a variety of structurally diverse xenobiotics. Induction of P-glycoprotein by the amplification of its gene has been identified as a major cause of resistance of tumor cells to the toxicity of a variety of anti-cancer drugs. The hepatic induction of P-glycoprotein may also contribute to acquired resistance of organisms to environmental toxicants. Continued elucidation of xenobiotic transport and transfer processes at the cellular levels will significantly advance our understanding of processes involved in xenobiotic toxicity and acquired resistance to chemical toxicity.

Growth inhibition of HIV-1-infected cells and membrane alterations induced by phosphatidylcholine

Cultured T-lymphoma cell lines H9 and KE37-1 permanently infected with human immunodeficiency virus (HIV-1, strain HTLV-III B) were exposed to phosphatidylcholine (PC) and a PC-containing formulation "Essentiale" (PC-E). PC and PC-E, but not triglyceride, were found to inhibit growth of virus-infected cells. Additionally, the membrane lipid composition of infected and uninfected H9 cells was investigated upon exposure to PC. The HIV-1-infected cells showed a 25% increase in membrane triglyceride content and a 15% increase in membrane phospholipid saturated fatty acids. In the presence of PC, there is a further increase in triglyceride content up to 180% compared with uninfected control cells, suggesting a possible cause for the selective growth inhibition of HIV-1-infected cells by PC. The PC-E dose range effective in vitro for inhibition of HIV-1-infected cell growth falls within the range that can be reached in vivo. Formulations containing PC are well tolerated by humans and might be applicable at an early stage of HIV-1 infection to reduce the number of virus-producing cells.

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

2,4,5,2',4'5'-Hexachlorobiphenyl (6-CB)--a polychlorinated biphenyl (PCB) congener resistant to metabolism in most species--has become a major residue in the biosphere including human adipose tissue. Its use as a model of unmetabolizable lipophilic compounds and as a tool in toxicokinetics in the last two decades is reviewed. This extremely water-insoluble compound is transported in plasma by albumin and lipoproteins. Binding to these plasma proteins appears to be important for uptake and release processes in different tissues. The redistribution kinetics of 6-CB as well as its pronounced adipose tissue storage and a very slow excretion with the faeces has been established in long-term animal studies. Excretion is strongly influenced by an increasing or diminishing adipose storage compartment size. Other minor pathways of elimination, e.g., via hair, become also important in the absence of metabolism and renal excretion. 6-CB has revealed the possibility of an almost quantitative transfer of the maternal body burden to the offspring via milk. The use of 6-CB in studies with tissue preparations in vitro is providing insight into transport mechanisms of uptake and release.

Transport of organochlorine residues in the rat and human blood

Organochlorine residues (OCR)2 are poorly soluble in water and are transported in the organism bound by the blood components. The distribution among blood fractions (cells/plasma, lipoproteins/rest of plasma proteins) were variable depending on the residue (HCB, p p'-DDE, HCH, Aroclor 1260, PCP) and on the species (rat, man). Differences were not found between in vivo (after oral single dosing) and in vitro (blood incubation) experiments. Results indicated a high affinity of organochlorine residues for lipoproteins; however, binding to blood carriers was very weak as demonstrated by the rapid release of residues by elution through a reverse phase column. The effects of residue binding to blood components on the distribution kinetics to tissues are discussed.

Photo-induced formation of DNA adducts of 2,2',4,4',5,5'-hexachlorobiphenyl in cultured human cells

Association of the PCB congener 2,2',4,4',5,5'-hexachlorobiphenyl (6-CB) with cell nuclei has been studied in cultured monolayer human Chang liver cells. Photo-induced formation of covalent bonds determined 6-CB binding to protein of cell nuclei and to DNA. Nuclear binding of 6-CB approached equilibrium after approximately 30 min of incubation. Photo-induced binding in vitro to purified Chang liver cell DNA substantiated direct interaction of the PCB congener with DNA. In monolayer cells, low levels of photo-induced 6-CB DNA adducts could be detected using the very sensitive 32P-postlabeling method. Adduct formation was dependent on 6-CB concentration as well as on incubation time. Highest adduct levels were in the range of 2 X 10(-8). Model reactions in vitro showed photo-induced binding of 6-CB to individual purine deoxyribonucleotide-3'-phosphates. The results demonstrate rapid intracellular movement of the PCB congener into the cell nucleus. The vast majority is associated with nuclear protein, minute amounts of 6-CB are found proximate to the DNA helix as evidenced by photo-induced adducts of purine nucleotides.

Photo-induced binding of 2,2',4,4',5,5'-hexachlorobiphenyl to cultured human cells

The polychlorinated biphenyl congener 2,2',4,4',5,5'-hexachlorobiphenyl can be photoactivated by brief high-intensity ultraviolet irradiation. Photoactivated intermediates are bound to neighboring biological macromolecules. Properties and stability of hexachlorobiphenyl photobinding were examined with bovine serum albumin, a protein known to strongly bind lipophilic compounds. Photobinding to cultured human Chang liver cells was a function of ligand and cell protein concentration as well as of irradiation time. Binding increased with incubation time, in support of the time course of uptake previously measured in the same system by alternative methods. Separation of cell proteins by gel electrophoresis showed that the distribution pattern of photobinding changed at different rates for different proteins. Photobinding to major cell lipid groups and to individual phospholipids likewise reflected uptake of the compound. Notably, photobinding to phosphatidyl choline was elevated relative to phosphatidyl ethanolamine. Thus, the presented method is suitable to follow up transport and intracellular equilibrium distribution of photoactivatable ligands. As a particular advantage, artefactual redistribution of persistent lipophilic compounds during cell fractionation can be avoided.