Lymphatic and portal vein absorption of organochlorine compounds in rats

Metabolic Consequences of the Water We Drink: A Study Based on Field Evidence and Animal Model Experimentation

The effect of the chronic consumption of water contaminated with residual concentrations of DDT's metabolites (DDD-dichlorodiphenyldichloroethane and DDE-dichlorodiphenyldichloroethylene) found in the environment were evaluated on the biometric, hematological and antioxidant system parameters of the hepatic, muscular, renal and nervous tissues of Wistar rats. The results showed that the studied concentrations (0.002 mg.L^-1 of DDD plus 0.005 mg.L^-1 of DDE) could not cause significant changes in the hematological parameters. However, the tissues showed significant alteration in the activity of the antioxidant system represented by the increase in the activity of the enzymes gluthathione S-transferases in the liver, superoxide dismutase in the kidney, gluthathione peroxidase in the brain, and several changes in enzymatic activity in muscle (SOD, GPx and LPO). The enzymes alanine aminotransaminase (ALT) and aspartate aminotransaminase (AST) were also evaluated for the amino acids' metabolism in the liver, with ALT showing a significant increase in the exposed animals. In the integrative analysis of biomarkers (Permanova and PCOA), the studied concentrations showed possible metabolic changes and damage to cellular structures evidenced by increased oxidative stress and body weight gain among the treated animals. This study highlights the need for further studies on the impact of banned pesticides still present in soils that may induce adverse effects in organisms that may prevail in future generations and the environment.

Partitioning of Persistent Organic Pollutants between Adipose Tissue and Serum in Human Studies

Blood is the most widely used matrix for biomonitoring of persistent organic pollutants (POPs). It is assumed that POPs are homogenously distributed within body lipids at steady state; however, the variability underlying the partitioning of POPs between fat compartments is poorly understood. Hence, the objective of this study was to review the state of the science about the relationships of POPs between adipose tissue and serum in humans. We conducted a narrative literature review of human observational studies reporting concentrations of POPs in paired samples of adipose tissue with other lipid-based compartments (e.g., serum lipids). The searches were conducted in SCOPUS and PUBMED. A meta-regression was performed to identify factors responsible for variability. All included studies reported high variability in the partition coefficients of POPs, mainly between adipose tissue and serum. The number of halogen atoms was the physicochemical variable most strongly and positively associated with the partition ratios, whereas body mass index was the main biological factor positively and significantly associated. To conclude, although this study provides a better understanding of partitioning of POPs to refine physiologically based pharmacokinetic and epidemiological models, further research is still needed to determine other key factors involved in the partitioning of POPs.

Development and Application of a Life-Stage Physiologically Based Pharmacokinetic (PBPK) Model to the Assessment of Internal Dose of Pyrethroids in Humans

To address concerns around age-related sensitivity to pyrethroids, a life-stage physiologically based pharmacokinetic (PBPK) model, supported by in vitro to in vivo extrapolation (IVIVE) was developed. The model was used to predict age-dependent changes in target tissue exposure of 8 pyrethroids; deltamethrin (DLM), cis-permethrin (CPM), trans-permethrin, esfenvalerate, cyphenothrin, cyhalothrin, cyfluthrin, and bifenthrin. A single model structure was used based on previous work in the rat. Intrinsic clearance (CLint) of each individual cytochrome P450 or carboxylesterase (CES) enzyme that are active for a given pyrethroid were measured in vitro, then biologically scaled to obtain in vivo age-specific total hepatic CLint. These IVIVE results indicate that, except for bifenthrin, CES enzymes are largely responsible for human hepatic metabolism (>50% contribution). Given the high efficiency and rapid maturation of CESs, clearance of the pyrethroids is very efficient across ages, leading to a blood flow-limited metabolism. Together with age-specific physiological parameters, in particular liver blood flow, the efficient metabolic clearance of pyrethroids across ages results in comparable to or even lower internal exposure in the target tissue (brain) in children than that in adults in response to the same level of exposure to a given pyrethroid (Cmax ratio in brain between 1- and 25-year old = 0.69, 0.93, and 0.94 for DLM, bifenthrin, and CPM, respectively). Our study demonstrated that a life-stage PBPK modeling approach, coupled with IVIVE, provides a robust framework for evaluating age-related differences in pharmacokinetics and internal target tissue exposure in humans for the pyrethroid class of chemicals.

Differential lymphatic versus portal vein uptake of the synthetic pyrethroids deltamethrin and cis-permethrin in rats

The objective of this study was to obtain data on pathways of absorption of the synthetic pyrethroids deltamethrin (DLM) and cis-permethrin (CPM) following oral administration to rats. Adult male Sprague-Dawley rats with cannulated mesenteric lymph ducts and hepatic portal veins were given single doses of either 5 mg/kg DLM or 60 mg/kg CPM via the duodenum and lymph and portal blood samples collected for up to 300 min. The pyrethroid dosing vehicles (5 mL/kg body weight) were either corn oil or glycerol formal. Levels of DLM and CPM in lymph and portal blood samples were determined by high-performance liquid chromatography-mass spectrometry-mass spectrometry. Over the time period studied, levels of both DLM and CPM following administration in either corn oil or glycerol formal were greater in lymph than in portal blood. Lymphatic uptake of both DLM and CPM was enhanced following dosing in glycerol formal than in corn oil. The results of this study suggest that after oral administration to rats, these two pyrethroids are predominantly absorbed via the lymphatic system rather than via portal blood. The data obtained in this study thus support a recently developed physiologically-based pharmacokinetic (PBPK) model to evaluate age-related differences in pyrethroid pharmacokinetics in the rat, where it was assumed that absorption of pyrethroids was predominantly via lymphatic uptake.

The challenging use and interpretation of blood biomarkers of exposure related to lipophilic endocrine disrupting chemicals in environmental health studies

The use of exposure biomarkers has been growing during the last decades, being considered the 'gold-standard' approach for individual exposure assessment to environmental chemicals. However, lipophilic endocrine disrupting chemicals (LEDC) have specific physicochemical and biological properties implying particular analytical challenges and interpretative caveats. The epidemiological literature is therefore afflicted by methodological inconsistencies and results divergences, in part due to recognised sources of exposure measurement error and misinterpretation of results. The aim of the present review is to identify external and endogenous sources of variability and uncertainty associated with the LEDC blood biomarkers in epidemiological studies. The dynamic nature of blood and an overview of the known mechanisms of transport, storage and partition of LEDCs in the organism are first described. The external sources of variability and uncertainty introduced at pre-analytical and analytical level are subsequently presented. Subsequently, we present some specific cases where the dynamics of lipids and LEDCs may be substantially modified and thus, the interpretation of biomarkers can be particularly challenging. The environmental obesogens as source of biomarkers variability is also discussed in the light of the most recent findings. Finally, different modelling approaches (statistical and pharmacokinetic models) proposed to improve the use and interpretation of biomarkers are appraised.

Colonic Absorption of Low-Molecular-Weight Metabolites Influenced by the Intestinal Microbiome: A Pilot Study

Low-molecular-weight metabolites produced by the intestinal microbiome play a direct role in health and disease. However, little is known about the ability of the colon to absorb these metabolites. It is also unclear whether these metabolites are bioavailable. Here, metabolomics techniques (capillary electrophoresis with time-of-flight mass spectrometry, CE-TOFMS), germ-free (GF) mice, and colonized (Ex-GF) mice were used to identify the colonic luminal metabolites transported to colonic tissue and/or blood. We focused on the differences in each metabolite between GF and Ex-GF mice to determine the identities of metabolites that are transported to the colon and/or blood. CE-TOFMS identified 170, 246, 166, and 193 metabolites in the colonic feces, colonic tissue, portal plasma, and cardiac plasma, respectively. We classified the metabolites according to the following influencing factors: (i) the membrane transport system of the colonocytes, (ii) metabolism during transcellular transport, and (iii) hepatic metabolism based on the similarity in the ratio of each metabolite between GF and Ex-GF mice and found 62 and 22 metabolites that appeared to be absorbed from the colonic lumen to colonocytes and blood, respectively. For example, 11 basic amino acids were transported to the systemic circulation from the colonic lumen. Furthermore, many low-molecular-weight metabolites influenced by the intestinal microbiome are bioavailable. The present study is the first to report the transportation of metabolites from the colonic lumen to colonocytes and somatic blood in vivo, and the present findings are critical for clarifying host-intestinal bacterial interactions.

Monosodium glutamate inhibits the lymphatic transport of lipids in the rat

It is not well understood how monosodium glutamate (MSG) affects gastrointestinal physiology, especially regarding the absorption and the subsequent transport of dietary lipids into lymph. Thus far, there is little information about how the ingestion of MSG affects the lipid lipolysis, uptake, intracellular esterification, and formation and secretion of chylomicrons. Using lymph fistula rats treated with the infusion of a 2% MSG solution before a continuous infusion of triglyceride, we show that MSG causes a significant decrease in both triglyceride and cholesterol secretion into lymph. Intriguingly, the diminished lymphatic transport of triglyceride and cholesterol was not caused by an accumulation of these labeled lipids in the intestinal lumen or in the intestinal mucosa. Rather, it is a result of increased portal transport in the animals fed acutely the lipid plus 2% MSG in the lipid emulsion. This is a first demonstration of MSG on intestinal lymphatic transport of lipids.

Endocrine Disruptor DDE Associated with a High-Fat Diet Enhances the Impairment of Liver Fatty Acid Composition in Rats

The banned pesticide dichlorodiphenyltrichloroethane (DDT) and its main metabolite, p,p'-dichlorodiphenyldichloroethylene (DDE), are commonly found in the food chain and in all tissues of living organisms. DDE is associated with metabolic diseases acting as an endocrine disruptor and more recently with the obesity pandemic. This study focuses on using fatty acid analysis to relate DDE exposure and metabolic dysfunction: liver and adipose tissue (visceral and subcutaneous) composition from male Wistar rats fed a standard (STD) or high-fat (HF) diet versus the addition of DDE in water. DDE exposure increased liver levels of palmitic, stearic, oleic, trans fatty, and linoleic acids having altered the n6 and n3 pathways leading to high concentrations of arachidonic acid and DHA (C22:6 n3). The results of this study confirm the close relationship between this pesticide metabolite and hepatic lipid dysfunction, underscoring its role as an emerging target for the prevention and therapy of nonalcoholic fatty liver disease (NAFLD).

An assessment of the intestinal lumen as a site for intervention in reducing body burdens of organochlorine compounds

Many individuals maintain a persistent body burden of organochlorine compounds (OCs) as well as other lipophilic compounds, largely as a result of airborne and dietary exposures. Ingested OCs are typically absorbed from the small intestine along with dietary lipids. Once in the body, stored OCs can mobilize from adipose tissue storage sites and, along with circulating OCs, are delivered into the small intestine via hepatic processing and biliary transport. Retained OCs are also transported into both the large and small intestinal lumen via non-biliary mechanisms involving both secretion and desquamation from enterocytes. OCs and some other toxicants can be reabsorbed from the intestine, however, they take part in enterohepatic circulation(EHC). While dietary fat facilitates the absorption of OCs from the small intestine, it has little effect on OCs within the large intestine. Non-absorbable dietary fats and fat absorption inhibitors, however, can reduce the re-absorption of OCs and other lipophiles involved in EHC and may enhance the secretion of these compounds into the large intestine—thereby hastening their elimination. Clinical studies are currently underway to determine the efficacy of using non-absorbable fats and inhibitors of fat absorption in facilitating the elimination of persistent body burdens of OCs and other lipophilic human contaminants.

Mesenteric lymphatic absorption and the pharmacokinetics of naringin and naringenin in the rat

The hypothesis for this study was that flavanoids and their glycoside are absorbed mainly through the portal vein to enter the liver for biotransformation and are only partially absorbed through the lymphatic duct. To verify this hypothesis, an unconscious, mesenteric lymphatic/portal vein/jugular vein/bile duct/duodenum-cannulated rat model was developed. Naringin was administered at dosages of 600 and 1000 mg/kg, and naringenin was given at 100 and 300 mg/kg by intraduodenal administration. Blood samples collected from the portal vein and jugular vein as well as lymphatic fluid were prepared by protein precipitation and then analyzed by high-performance liquid chromatography with photodiode array detection (HPLC-DAD). Analyses of these samples were doubly confirmed by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). The results show that, after intraduodenal administration, both compounds were mainly absorbed into portal blood rather than mesenteric lymph, and most of the intact analyte would be eliminated through bile excretion. The area under the concentration (AUC) ratio was defined to represent the absorption ratio for portal vein [AUC(portal)/AUC((portal+lymph))] and lymph fluid [AUC(lymph)/AUC((portal+lymph))]. The results indicate that the portal and lymphatic absorptions for naringin were around 95 and 5.0%, respectively. The respective absorptions for naringenin were around 98 and 2%, respectively.

Methods for studying rodent intestinal lipoprotein production and metabolism

Lipid absorption begins with the digestion of dietary triacylglycerol and ultimately results in the secretion of triacylglycerol in chylomicrons into the lymphatics. Additionally, the intestine also secretes numerous proteins and peptides involved in lipid and lipoprotein metabolism in response to food. Ultimately, chylomicrons and these proteins, peptides, and hormones are found in lymph. The lymph fistula rat model has traditionally been used to study this intestinal absorption of nutrients, especially lipids, but recently, this model has also been used for studying the secretion of hormones by the small intestine. The protocols described in this article include the lymph fistula rat and mouse model, as well as in vivo chylomicron metabolism studies. These experimental models are helpful for the study of metabolic phenotypes, the characterization of intestinal lipid absorption and transport, and determining peripheral metabolism of intestinally derived lipoproteins.

The transport of DDT from chylomicrons to adipocytes does not mimic triacylglycerol transport

Despite being banned in the U.S., organochlorine toxins such as DDT are frequently detected in human adipose tissue. The main route of exposure is through the consumption of contaminated foods and subsequent intestinal packaging of DDT into chylomicrons. These chylomicrons, which also contain dietary triacylglycerol (TG), are delivered directly to peripheral tissues without first being metabolized by the liver. The physiological process by which these compounds are delivered from chylomicrons to adipose is not well understood, but is clinically relevant since it bypasses first-pass metabolism. Based on its highly lipophilic nature, it has been assumed that DDT is transferred to peripheral tissues similar to TG; however, this has not been measured. Here, we use the lymph fistula rat to isolate chylomicrons containing both DDT and TG. These chylomicrons are the in vivo DDT delivery vehicle. Using 3T3-L1 adipocytes, we investigated the rate at which DDT transfers from chylomicrons to adipocytes, and mediators of this process. This novel approach closely approximates the in vivo DDT exposure route. We show that: 1) DDT repartitions from chylomicrons to adipocytes, 2) this transport does not require hydrolysis of TG within the chylomicron, and is stimulated by the inhibition of LPL, 3) albumin does not inhibit DDT uptake, 4) DDT dissolved in DMSO does not appropriately mimic in vivo DDT transport; and most importantly, 5) DDT uptake from chylomicrons does not mimic the uptake of TG from the same particles. Understanding these factors is important for designing interventions for human populations exposed to DDT.

Using the lymphatics to study nutrient absorption and the secretion of gastrointestinal hormones

The lymph fistula rat model has traditionally been used to study the intestinal absorption of nutrients, especially lipids, but recently this model has also been used for studying the secretion of incretin hormones by the small intestine. The small intestine is not only responsible for the digestion and transport of dietary triacylglycerol, through the formation of chylomicrons, but it also secretes the incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) from enteroendocrine cells. Ultimately, both chylomicrons and incretins are found in lymph. Advantages of the lymph fistula rat model in studying chylomicron and incretin secretion are numerous and include: 1) the concentrations of incretin hormones are higher in lymph than in peripheral or portal plasma; 2) there is reduced degradation of incretin hormones by DPP-IV in the lymph compartment; 3) less dilution by the circulating fluid; 4) this model allows the continuous collection of lymph from conscious animals, eliminating any potential side effects on lymph flow and gastrointestinal function due to anesthesia; and finally, and perhaps most importantly, and 5) the concentration in the intestinal lymph provides a physiologically accurate representation of the hormonal milieu within the intestinal mucosa where incretins may interact with enteroendocrine and/or dendritic cells and signal through the enteric or autonomic neurons. The importance of GIP and GLP-1 in health and disease is becoming more apparent, especially as the prevalence of type 2 diabetes and other metabolic disorders increases. This review focuses on the use of the lymph fistula rat as a model to study the secretion of incretins, as well as dietary lipid.

Intestinal lymphatic transport for drug delivery

Intestinal lymphatic transport has been shown to be an absorptive pathway following oral administration of lipids and an increasing number of lipophilic drugs, which once absorbed, diffuse across the intestinal enterocyte and while in transit associate with secretable enterocyte lipoproteins. The chylomicron-associated drug is then secreted from the enterocyte into the lymphatic circulation, rather than the portal circulation, thus avoiding the metabolically-active liver, but still ultimately returning to the systemic circulation. Because of this parallel and potentially alternative absorptive pathway, first-pass metabolism can be reduced while increasing lymphatic drug exposure, which opens the potential for novel therapeutic modalities and allows the implementation of lipid-based drug delivery systems. This review discusses the physiological features of the lymphatics, enterocyte uptake and metabolism, links between drug transport and lipid digestion/re-acylation, experimental model (in vivo, in vitro, and in silico) of lymphatic transport, and the design of lipid- or prodrug-based drug delivery systems for enhancing lymphatic drug transport.