Polychlorinated biphenyl uptake and transport by lymph and plasma components

Maternal Transfer of Persistent Organic Pollutants to Sea Turtle Eggs: A Meta-Analysis Addressing Knowledge and Data Gaps Toward an Improved Synthesis of Research Outputs

Maternal transfer of persistent organic pollutants (POPs) confronts developing embryos with a pollution legacy and poses conservation concerns due to its potential impacts unto subsequent generations. We conducted a systematic review focusing on: 1) processes of POP maternal transfer, 2) challenges and opportunities to synthesizing current knowledge on POP concentrations in eggs, and 3) a meta-analysis of patterns in current egg pollution data. Results suggest selective maternal transfer of individual compounds. These relate to biological factors such as the foraging and remigration behavior, and to the selective mobilization of POPs during vitellogenesis, such as increased diffusion limitation for lipophilic POPs and slower release and higher reabsorption of apolar POPs. A key gap relates to knowledge of further selective toxicokinetics during embryonic development, as research to date has mainly focused on initial uptake into eggs. Challenges in the synthesis of current data on egg contamination profiles relate to methodological differences, varying analytical approaches, restricted data access, and reporting transparency among studies. To increase opportunities in the use of current data, we propose best practice guidelines, and synthesize a database on POP concentrations within sea turtle eggs. The meta-analysis revealed a geographical and taxonomic bias on the West Atlantic Ocean, including the Gulf of Mexico and Caribbean Sea, with most studies conducted on green turtles. Concentrations of POPs show temporal patterns related to trends in usage, production, release, and persistence in the environment, often with regional patterns. The trophic level has the potential to influence POP patterns with higher concentrations in loggerheads compared to other species, but this is confounded by temporal and geographic trends. We argue for more mechanistically process-focused and methodologically comparable research. Environ Toxicol Chem 2019;39:9-29. © 2019 SETAC.

Intestinal Lymphatic Transport: an Overlooked Pathway for Understanding Absorption of Plant Secondary Compounds in Vertebrate Herbivores

Herbivores employ numerous strategies to reduce their exposure to toxic plant secondary chemicals (PSCs). However, the physiological mechanisms of PSC absorption have not been extensively explored. In particular, the absorption of PSCs via intestinal lymphatic absorption has been largely overlooked in herbivores, even though this pathway is well recognized for pharmaceutical uptake. Here, we investigated for the first time whether PSCs might be absorbed by lymphatic transport. We fed woodrats (Neotoma albigula) diets with increasing concentrations of terpene-rich juniper (Juniperus monosperma) either with or without a compound that blocks intestinal lymphatic absorption (Pluronic L-81). Woodrats consuming diets that contained the intestinal lymphatic absorption blocker exhibited increased food intakes and maintained higher body masses on juniper diets. Our study represents the first demonstration that PSCs may be absorbed by intestinal lymphatic absorption. This absorption pathway has numerous implications for the metabolism and distribution of PSCs in the systemic circulation, given that compounds absorbed via lymphatic transport bypass first-pass hepatic metabolism. The area of lymphatic transport of PSCs represents an understudied physiological pathway in plant-herbivore interactions.

Chiral polychlorinated biphenyls: absorption, metabolism and excretion--a review

Seventy eight out of the 209 possible polychlorinated biphenyl (PCB) congeners are chiral, 19 of which exist under ambient conditions as stable rotational isomers that are non-superimposable mirror images of each other. These congeners (C-PCBs) represent up to 6 % by weight of technical PCB mixtures and undergo considerable atropisomeric enrichment in wildlife, laboratory animals, and humans. The objective of this review is to summarize our current knowledge of the processes involved in the absorption, metabolism, and excretion of C-PCBs and their metabolites in laboratory animals and humans. C-PCBs are absorbed and excreted by passive diffusion, a process that, like other physicochemical processes, is inherently not atropselective. In mammals, metabolism by cytochrome P450 (P450) enzymes represents a major route of elimination for many C-PCBs. In vitro studies demonstrate that C-PCBs with a 2,3,6-trichlorosubstitution pattern in one phenyl ring are readily oxidized to hydroxylated PCB metabolites (HO-PCBs) by P450 enzymes, such as rat CYP2B1, human CYP2B6, and dog CYP2B11. The oxidation of C-PCBs is atropselective, thus resulting in a species- and congener-dependent atropisomeric enrichment of C-PCBs and their metabolites. This atropisomeric enrichment of C-PCBs and their metabolites likely plays a poorly understood role in the atropselective toxicity of C-PCBs and, therefore, warrants further investigation.

The role of caveolae in endothelial cell dysfunction with a focus on nutrition and environmental toxicants

Complications of vascular diseases, including atherosclerosis, are the number one cause of death in Western societies. Dysfunction of endothelial cells is a critical underlying cause of the pathology of atherosclerosis. Lipid rafts, and especially caveolae, are enriched in endothelial cells, and down-regulation of the caveolin-1 gene may provide protection against the development of atherosclerosis. There is substantial evidence that exposure to environmental pollution is linked to cardiovascular mortality, and that persistent organic pollutants can markedly contribute to endothelial cell dysfunction and an increase in vascular inflammation. Nutrition can modulate the toxicity of environmental pollutants, and evidence suggests that these affect health and disease outcome associated with chemical insults. Because caveolae can provide a regulatory platform for pro-inflammatory signalling associated with vascular diseases such as atherosclerosis, we suggest a link between atherogenic risk and functional changes of caveolae by environmental factors such as dietary lipids and organic pollutants. For example, we have evidence that endothelial caveolae play a role in uptake of persistent organic pollutants, an event associated with subsequent production of inflammatory mediators. Functional properties of caveolae can be modulated by nutrition, such as dietary lipids (e.g. fatty acids) and plant-derived polyphenols (e.g. flavonoids), which change activation of caveolae-associated signalling proteins. The following review will focus on caveolae providing a platform for pro-inflammatory signalling, and the role of caveolae in endothelial cell functional changes associated with environmental mediators such as nutrients and toxicants, which are known to modulate the pathology of vascular diseases.

Enantioselective disposition of PCB 136 (2,2',3,3',6,6'-hexachlorobiphenyl) in C57BL/6 mice after oral and intraperitoneal administration

Studies of xenobiotic disposition in rodents often employ experimental designs using differing routes of administration. In an effort to investigate the effects of route of administration on enantioselective disposition of xenobiotics, a chiral polychlorinated biphenyl (PCB), racemic PCB 136, was administered as a single dose (50 mg/kg body weight) to male or female C57BL/6 mice either orally or via intraperitoneal injection. Mice were sacrificed after either 3 or 6 days, and blood and organs were collected for PCB analysis. Intraperitoneal injection of PCB 136 produced statistically higher PCB levels in blood and organs than did the oral administration. Tissue levels were higher after 3 days than those after 6 days. Enantioselective analysis showed that (+)-PCB 136 was enriched in most organs, with the most pronounced enrichment found in the liver and the brain of animals dosed orally or by intraperitoneal injection, respectively. Significantly higher retained enantiomeric fractions of PCB 136 were found in the oral treatment groups compared with those found in intraperitoneal treatment groups, possibly as a result of the lower PCB levels in oral treatment groups. Therefore, the choice of administration route may well have implications for the enantioselective disposition of PCB 136 and other chiral substances.

Effect of Chlorella pyrenoidosa on fecal excretion and liver accumulation of polychlorinated dibenzo-p-dioxin in mice

The effect of Chlorella pyrenoidosa on fecal excretion and liver accumulation of polychlorinated dibenzo-p-dioxin in C57BL/6N mice administered dioxin was examined. Mice were administered 2.2 microg of 1,2,3,4,7,8-hexachlorodibenzo-p-dioxin (H6CDD) dissolved in corn oil once after a period of acclimatization, after which they were fed either a basal diet, a 10% C. pyrenoidosa diet, or a 10% Spinach diet, for five weeks. Among mice fed the 10% C. pyrenoidosa diet, cumulative fecal excretion of H6CDD over the first week following administration was significantly greater (9.2-fold) than that observed among mice fed the basal diet. Moreover, excretion during the fifth week following administration of H6CDD was still significantly greater (3.1-fold) among mice fed the 10% C. pyrenoidosa diet than among mice fed the basal diet. Five weeks after administration of H6CDD, liver accumulation of H6CDD in mice fed the 10% C. pyrenoidosa diet was significantly less than that observed among mice fed either the basal diet and the Spinach diet (by 27.9% and 34.8%, respectively). These findings suggest that C. pyrenoidosa may be useful in inhibiting the absorption of dioxins via food and the reabsorption of dioxins stored already in the body in the intestinal tract, thus preventing accumulation of dioxins within the body.

Enhancement of oral moxidectin bioavailability in rabbits by lipid co-administration

Moxidectin is a member of the macrocyclic lactone family of drugs widely used for the control of internal and external parasites. Because moxidectin is highly lipophilic, we suspect that lymphatic transport influences the intestinal absorption of oral formulations of the drug. We studied the influence of lipid co-administration on the pharmacokinetics of an oral formulation of moxidectin in rabbits. Ten rabbits were orally administered 0.3 mg kg(-1) moxidectin with or without sunflower oil. Moxidectin and triglyceride were analyzed in plasma over 23 days. Sunflower oil co-administration significantly increased the area under the plasma concentration-time curve of moxidectin (98%, P<0.05) and prolonged its mean residence time from 1.52 days to 2.12 days (P<0.04). Simultaneously, an increase in plasma triglyceride was observed in response to oil administration. It is suggested that lipid administration increases the systemic availability of oral moxidectin by enhancing the extent of intestinal lymphatic transport of the drug. Lipid-based formulations should improve the bioavailability of moxidectin in rabbits.

A stepwise surgical procedure to investigate the lymphatic transport of lipid-based oral drug formulations: Cannulation of the mesenteric and thoracic lymph ducts within the rat

INTRODUCTION

A number of animal models have been described for the assessment of intestinal lymphatic drug transport. Lymphatic transport studies are commonly first conducted in the laboratory rat, with larger more complicated models (i.e., dog or pig) subsequently investigated. However, the utility of lymph fistulation in large animals is limited by considerable logistical and economic constraints.

METHODS

This paper describes a stepwise surgical procedure for cannulating the thoracic and mesenteric lymph ducts in male Sprague-Dawley rats.

RESULTS

Following surgery, thoracic and mesenteric lymph flow rates during the 24-h period immediately following surgery averaged 12.5+/-2.5 and 2.4+/-1.1 ml/h, respectively. This flow rate is greater than that obtained with previously described methods, which require restraint of the animals and/or a 24-h recovery period and are reported to produce average intestinal lymph flow rates of 2 ml/h.

DISCUSSION

This animal model can be utilized for the assessment of drug transport by the lymphatics and for determining what percentage of lymphatic transport is a result of only intestinal lymphatics.

Polychlorinated biphenyls in broiler diets: their digestibility and incorporation in body tissues

The influence of dietary amounts of polychlorinated biphenyls (PCBs) was studied on performance, apparent PCB digestibility and PCB accumulation in broiler chickens that were maintained until 42 days of age. Dietary concentrations of supplemented PCBs, based on the sum of seven reference congeners, ranged from 0 to 12 ng/g, which was below the legal maximum of 200 ng PCBs/g fat in Belgian feeds. PCB ingestion did not significantly affect body weight and feed intake. Apparent PCB digestibility was not influenced by dietary levels of added fat varying between 4% and 8%, but was significantly higher in broilers fed diets containing added PCBs. Accumulation of PCBs in the fat fraction of abdominal adipose tissue and breast and thigh muscle greatly depended upon PCB intake. However, PCB contents in the various body fat fractions within the same animal differed, even within muscle tissues, indicating an unequal PCB distribution in body fats.

The role of lymphatic transport in enhancing oral protein and peptide drug delivery

The gastrointestinal lymphatic system is a specific transport pathway through which dietary lipids, fat-soluble vitamins, and water-insoluble peptide-type molecules (e.g., cyclosporine A) can gain access to the systemic circulation. Drugs transported by way of the gastrointestinal lymphatic system bypass the liver and avoid potential hepatic first-pass metabolism. Lymphatic delivery of immunomodulatory and low therapeutic index protein and peptide drugs used in the treatment of cancer cell metastases and HIV presents an opportunity to maximize therapeutic benefit while minimizing general systemic drug exposure. Furthermore, lymphatic drug transport may promote drug incorporation into the body's lipid-handling system, thus offering the potential to manipulate drug distribution and residence time within the body. This review article will discuss the potential utilization of lymphatic transport in enhancing the oral absorption of protein- and peptide-like drugs.

Factors affecting the storage and excretion of toxic lipophilic xenobiotics

Lipophilic toxins have been introduced into the environment both as functional compounds, such as pesticides, and as industrial waste from incineration or the manufacture of electrical transformer components. Among these substances are compounds that are carcinogenic and that affect the endocrine system. Accidental high exposures of humans to some lipophilic toxins have produced overt disease symptoms including chloracne and altered liver function. These toxic materials have been the recent focus of international effort to reduce or eliminate classes of halogenated hydrocarbons from the environment. Evidence of the widespread distribution of lipophilic toxins in the biosphere has been obtained by analyses of human tissues and human milk. The principal route of entry of lipophilic toxins into humans is through the food chain, and most of them are stored in adipose tissue. A common route of excretion is in bile, but there is also evidence of nonbiliary excretion into the intestine. Enterohepatic circulation of many of these compounds slows their removal from the body. Substances that interrupt the enterohepatic circulation of compounds that enter the intestine by the biliary and nonbiliary routes increase the rate of their removal from the body and reduce their storage half-lives. Reduction in body fat, along with these dietary substances that interrupt enterohepatic circulation, further enhances the excretion rate. Areas for further research include optimizing regimens for body burden reductions, understanding the nature of nonbiliary excretion, and following the effects of tissue redistribution during loss of body fat.

Gastrointestinal uptake and vascular transport of 2,4'-dichlorobiphenyl

Absorption from the gastrointestinal tract and subsequent vascular transport of [3H]-2,4'-dichlorobiphenyl (Aroclor 1232; DCB) was investigated in an ovine model system. Rapid uptake of DCB and transport as a component of blood plasma without prior occurrence in thoracic duct lymph indicates that DCB was absorbed directly via the gastric mucosa with water soluble compounds. [3H]-DCB did not circulate associated with plasma lipid fractions in vivo, and did not bind to or sequester within plasma lipids in vitro. HPLC analysis of plasma fractions treated in vitro showed DCB to elute within a molecular weight range consistent with unbound product. Further, [3H]-DCB-derived label was associated with low molecular weight plasma components in vivo. Essentially the same elution profile was seen for [3H]-DCB-derived label found in urine. Metabolism of DCB as a function of time resulted in the apparent formation of a biotransformed product(s) that circulated with a plasma fraction(s) at the low end of the albumin molecular size range. These data suggest that DCB was not absorbed and transported in a manner typical of polychlorinated biphenyls with a higher chlorine content; rather, that it was absorbed, transported within the vascular system, and excreted in a pattern typical of a water soluble compound.

Distribution of toxaphene, DDT, and PCB among lipoprotein fractions in rat and human plasma

The distribution of 14C-toxaphene, 14C-DDT, and 14C-PCB among lipoprotein fractions was studied in vitro and in vivo using rat and human plasma. The association of these substances with rat plasma fractions was similar in both in vitro and in vivo experiments. Thirty-seven to fifty-two per cent of the total radioactivity was associated with the cholesterol-rich high density lipoproteins (HDL2, d = 1.075-1.21 g/ml) and 18-52% was recovered in the albumin-rich bottom fraction (BF, d greater than 1.21 g/ml). A time-dependent redistribution of the radioactivity from the lipoprotein fractions to the BF was also observed in the in vivo studies. In human plasma, the distribution of the three compounds was different and uncorrelated to the cholesterol level of the individual lipoprotein fractions. Toxaphene was almost equally distributed between BF (d greater than 1.21 ml), HDL (d = 1.063-1.21 g/ml) and low density lipoproteins (LDL, d = 1.006-1.063 g/ml) (26%, 27% and 29%, respectively), while only 18% appeared in the very low density lipoprotein (VLDL, d less than 1.006) fraction. In contrast, a large proportion of DDT and PCB radioactivity was recovered in the BF (52% and 62%, respectively) while only 38-48% was present in lipoprotein fractions. The complex nature of the interaction between xenobiotics and plasma lipoproteins is discussed.

Lipoprotein-mediated transfer of 2,4,5,2',4',5'-hexachlorobiphenyl into cultured human cells

1. The very low density, low density and high density lipoproteins (VLDL, LDL, HDL), centrifugally separated from human plasma treated with 2,4,5,2',4',5'-hexachloro[14C]biphenyl (14C-HCB) contained approximately 50% of the 14C-HCB. 2. Normal skin fibroblasts were incubated at 4 degrees C for 37 degrees C for varying times with medium containing 10% serum, LDL or HDL labelled with 14C-HCB. Cellular incorporation of 14C-HCB from serum was temperature-dependent and occurred mainly during the first 30 minutes. Cellular accumulation of 14C-HCB from isolated lipoproteins was also rapid and was more efficient from HDL than from LDL or serum. Accumulation from HDL was concentration-dependent and temperature-dependent. 3. The efflux of 14C-HCB from cells into serum- or lipoprotein-containing medium occurred very rapidly and was most effective in the presence of 20% serum. The order of efficiency in removal of HCB from cells was 20% serum, 50 micrograms LDL protein/ml, and 120 micrograms HDL protein/ml. Little or no efflux from cells occurred into serum-free, lipoprotein-free medium. 4. HDL may be involved in the delivery of HCB to cells, a role in contrast to the generally accepted theory that HDL transports lipids from cells.