Ultrastructural, protein, and lipid changes in liver associated with chlordecone treatment of mice

Compartmental models for apical efflux by P-glycoprotein--part 1: evaluation of model complexity

PURPOSE

With the goal of quantifying P-gp transport kinetics, Part 1 of these manuscripts evaluates different compartmental models and Part 2 applies these models to kinetic data.

METHODS

Models were developed to simulate the effect of apical efflux transporters on intracellular concentrations of six drugs. The effect of experimental variability on model predictions was evaluated. Several models were evaluated, and characteristics including membrane configuration, lipid content, and apical surface area (asa) were varied.

RESULTS

Passive permeabilities from MDCK-MDR1 cells in the presence of cyclosporine gave lower model errors than from MDCK control cells. Consistent with the results in Part 2, model configuration had little impact on calculated model errors. The 5-compartment model was the simplest model that reproduced experimental lag times. Lipid content and asa had minimal effect on model errors, predicted lag times, and intracellular concentrations. Including endogenous basolateral uptake activity can decrease model errors. Models with and without explicit membrane barriers differed markedly in their predicted intracellular concentrations for basolateral drug exposure. Single point data resulted in clearances similar to time course data.

CONCLUSIONS

Compartmental models are useful to evaluate the impact of efflux transporters on intracellular concentrations. Whereas a 3-compartment model may be sufficient to predict the impact of transporters that efflux drugs from the cell, a 5-compartment model with explicit membranes may be required to predict intracellular concentrations when efflux occurs from the membrane. More complex models including additional compartments may be unnecessary.

DDT and Other Chlorinated Insecticides

The use of organochlorine insecticides such as DDT, lindane and cyclodieneshas declined markedly worldwide over the last decades. Most are now banned or not used. At an acute toxicity level they have been relatively safe in use for humans. However, the greatest concerns are their persistence in people, wildlife and the environment due to their slow metabolism. Although their carcinogenicity for humans has not been supported by strong epidemiological evidence, their potential to be modulators of endocrine and immune function at levels remaining in the environment or associated with residual spraying of DDT continue to be of concern. At present, DDT is still allowed by the United Nations for combating malaria, with continual monitoring and assessment where possible. The toxicological consequences of exposure of animals and people to DDT is discussed as well as some analogues and other insecticides such as lindane, dieldrin and chlordecone that, although little used, continue to persist in surroundings and people. Because of circumstances of world health brought about by climate change or human activities that have yet to develop, there may come a time when the importance of some may re-emerge.

Chlordecone, a mixed pregnane X receptor (PXR) and estrogen receptor alpha (ERalpha) agonist, alters cholesterol homeostasis and lipoprotein metabolism in C57BL/6 mice

Chlordecone (CD) is one of many banned organochlorine (OC) insecticides that are widespread persistent organic pollutants. OC insecticides alter lipid homeostasis in rodents at doses that are not neurotoxic or carcinogenic. Pretreatment of mice or rats with CD altered tissue distribution of a subsequent dose of [(14)C]CD or [(14)C]cholesterol (CH). Nuclear receptors regulate expression of genes important in the homeostasis of CH and other lipids. In this study, we report that CD suppresses in vitro reporter systems for human liver X receptors (LXRs) and activates those for human farnesoid X receptor (FXR), pregnane X receptor (PXR) and estrogen receptor alpha (ERalpha) in a concentration-dependent manner (0-50 muM). Consistent with human PXR activation in vitro, three days after a single dose of CD (15 mg/kg) hepatic microsomal CYP3A11 protein increases in C57BL/6 mice. CD decreases hepatic CH ester content without altering total CH concentration. Apolipoprotein A-I (apoA-I) contents of hepatic lipoprotein-rich and microsomal fractions of CD-treated mice are higher than controls. There is a significant reduction in non-high density lipoprotein CH but not apolipoprotein B-48/100 (apoB-48/100) in plasma from CD-treated mice after a 4 h fast. At 14 days after 15 mg CD/kg apoA-I and apoB-100 proteins but not CYP3A11 protein in hepatic microsomes are similar to controls. This work indicates that altered CH homeostasis is a mode of OC insecticide action of relevance after a single dose. This at least partially explains altered CH tissue distribution in CD-pretreated mice.

An environmentally-relevant mixture of organochlorines and its vehicle control, dimethylsulfoxide, induce ultrastructural alterations in porcine oocytes

Organochlorine chemicals accumulate in the environment, particularly in the Arctic, and constitute potential developmental hazards to wildlife and human health. Although some of their harmful effects are recognized, their mechanisms of action within the target cells need to be better understood. This study was designed to test the hypothesis that an environmentally-relevant organochlorine mixture alters oocyte ultrastructure in the porcine model. Immature cumulus-oocyte complexes (COCs), partially cultured (18 hr) COCs without treatment or exposed to the organochlorine mixture or its vehicle (0.1% dimethysulfoxide; DMSO) during culture were processed for light and transmission electronic microscopy (TEM). The organochlorines induced major ultrastructural changes in the COCs: decreased density of the lipid droplets, increased smooth endoplasmic reticulum (SER) volume and increased interactions among SER, mitochondria, lipid droplets and vesicles. We suggest that these ultrastructural changes facilitate energy formation necessary to produce metabolizing enzymes. Other ultrastructural changes may reflect some degree of organochlorine toxicity: fewer gap junctions and decreased electron density of the cortical granules. Unexpectedly, the DMSO control treatment also induced similar ultrastructural changes, but to a lesser degree than the organochlorine mixture. This study is the first to demonstrate the effect of environmental contaminants on mammalian oocyte ultrastructure.