Enteric transport of chlordecone (Kepone) in the rat

Design of a generic model based on physiology for persistent organic pollutants in laying hens: Applications on chlordecone and chlorinated paraffins

A Physiology Based Pharmacokinetic (PBPK) model has been developed to predict the kinetics of Persistent Organic Pollutants (POPs) in laying hens. Different datasets have enabled the calibration of the model for chlordecone (CLD), an organochlorine pesticide used in the French West Indies between 1972 and 1993, as well as for chlorinated paraffins (CPs), widely used for various industrial applications worldwide. For this purpose, the sensitivity analysis showed that intake parameters, laying rate, partition coefficients of yolk, hepatic clearance, percentage of metabolism and age were key parameters. Applied to CLD and CPs, this model shows a good capacity for prediction, with 88 % of the experimental values ranging within 1.5-fold of the predicted value at steady state for CPs and 100 % for CLD. The fine modelling of the physiology and the laying process contributes to precision of the model and gives genericity, enabling the switch from one bird species to another. The model can be implemented with other POPs if the clearance and partition coefficient are known.

Chlordecone: development of a physiologically based pharmacokinetic tool to support human health risks assessments

Chlordecone (CD; Kepone™) is a carcinogenic organochlorine insecticide with neurological, reproductive, and developmental toxicity that was widely used in the French West Indies (FWI) from 1973 to 1993 to fight banana weevils. Although CD has not been used there for more than 25 years, it still persists in the environment and has polluted the waterways and soil of current and older banana fields. Today, human exposure to CD in the FWI mainly arises from consuming contaminated foodstuffs. The aims of this study were to develop a physiologically based pharmacokinetic (PBPK) model in the rat and extrapolate it to humans based on available pharmacokinetic data in the literature. A comparison of simulations using the rat model with published experimental datasets showed reasonable predictability for single and repetitive doses, and, thus, it was extrapolated to humans. The human PBPK model, which has seven compartments, is able to simulate the blood concentrations of CD in human populations and estimate the corresponding external dose using the reverse dosimetry approach. The human PBPK model will make it possible to improve quantitative health risk assessments for CD contamination and reassess the current chronic toxicological reference values to protect the FWI population.

Comparison of chlordecone and NDL-PCB decontamination dynamics in growing male kids after cessation of oral exposure: Is there a potential to decrease the body levels of these pollutants by dietary supplementation of activated carbon or paraffin oil?

Sixteen weaned male Alpine kids (Capra hircus) were subjected to a 21-day oral daily exposure of 0.05 mg kg^-1 BW. d^-1 of chlordecone (CLD) and 0.30 μg kg^-1 BW. d^-1 of each non-dioxin-like polychlorinated biphenyls (NDL-PCBs, congeners 28, 52, 101, 138, 153 and 180). Four kids, identified as the CONTA group, were slaughtered at the end of the exposure, while the remaining animals (n = 12) were fed with specific diets for an additional 21-day decontamination period before slaughtering. Kids from the DECONTA (n = 4) group were fed a control diet, while those from the AC10% and PO8% group received pellets supplemented with 10% activated carbon (AC) and 8% paraffin oil (PO), respectively. CLD and NDL-PCB levels in blood, liver, peri-renal fat and muscles from different groups were analysed to compare the decontamination dynamics of the pollutants and to determine the efficiency of AC and PO to decrease the body levels of pollutants. After the decontamination period, the CLD levels considerably decreased (more than 60%) in blood, liver, muscles and fat. Concerning NDL-PCBs, the decontamination process was much lower. Overall, CLD appeared to be less retained in kids' organism compared with NDL-PCBs, and the decontamination dynamics of these pollutants appeared to be different because of their specific physicochemical properties and lipophilicity. Furthermore, the dietary supplementation with AC or PO did not significantly affect the decontamination dynamics.

Determination of ADME and bioavailability following intravenous, oral, and dermal routes of exposure

Humans are exposed to chemicals either voluntarily or involuntarily through several routes. Therapeutic drugs are introduced into the human system via a number of routes including, but not limited to, oral, inhalation, intravenous (i.v.), topical, and subcutaneous. For occupational and environmental chemicals, the major routes of human exposure are inhalation, dermal, and oral. To determine the extent of exposure to chemicals, the concentration of the active molecules is measured in a biological medium. Determination of absolute and/or relative bioavailability of occupational and environmental chemical exposure through different routes is critical in understanding the risk to the general population of a low-level exposure to these chemicals. This unit describes typical protocol designs to generate data for the calculation of absorption, distribution, metabolism, and elimination (ADME) and absolute and relative bioavailability of chemicals when exposed through i.v., oral, and dermal routes.

Physiologically based pharmacokinetic/toxicokinetic modeling

Physiologically based pharmacokinetic (PBPK) models differ from conventional compartmental pharmacokinetic models in that they are based to a large extent on the actual physiology of the organism. The application of pharmacokinetics to toxicology or risk assessment requires that the toxic effects in a particular tissue are related in some way to the concentration time course of an active form of the substance in that tissue. The motivation for applying pharmacokinetics is the expectation that the observed effects of a chemical will be more simply and directly related to a measure of target tissue exposure than to a measure of administered dose. The goal of this work is to provide the reader with an understanding of PBPK modeling and its utility as well as the procedures used in the development and implementation of a model to chemical safety assessment using the styrene PBPK model as an example.

Reduced oral itraconazole bioavailability by antacid suspension

AIMS

To investigate the effects of antacid suspension on oral absorption of itraconazole.

METHODS

A randomized, open-labelled, two-period, crossover study with a 1-week washout period was conducted in 12 healthy Thai male volunteers. The participants were allocated in either treatment A or B in the first period. In treatment A, the volunteers were orally administered with 200 mg of itraconazole alone. In treatment B, the volunteers were administered orally with 200 mg of itraconazole co-administered with antacid suspension. Serial serum samples were collected over the period of 24 h and subsequently analysed by using a validated high-pressure liquid chromatographic method with ultraviolet detection. Pharmacokinetic parameters were determined by non-compartmental analysis.

RESULTS

Time to reach maximal concentration (Tmax), maximal concentration (Cmax) and area under the curve (AUC0-infinity) were markedly decreased in antacid-treated group. Tmax for treatment A was 3.0 +/- 0.4 and 5.1 +/- 2.7 h for treatment B. Cmax and AUC0-infinity of treatments A and B were 146.3 +/- 70.5 vs. 43.6 +/- 16.9 (ng/mL) and 1928.5 +/- 1114.6 vs. 654.8 +/- 452.2 (ng x h/mL) respectively. 90% Confidence interval (90% CI) of Cmax and AUC0--infinity were 24.1-42.1 and 16.2-65.9 respectively.

CONCLUSIONS

Rate and extent of itraconazole oral absorption were markedly decreased by concurrent use of antacid suspension. Hence, co-administration of itraconazole and antacid suspension should be avoided.

Pharmacokinetic–pharmacodynamic modelling of the schedule-dependent effect of the anti-cancer agent CHS 828 in a rat hollow fibre model

N-(6-Chlorophenoxyhexyl)-N'-cyano-N''-4-pyridylguanidine (CHS 828) is a novel anticancer agent that shows schedule-dependent effects in vitro and in vivo, as well as in Phase I clinical trials. A rat hollow fibre model was used to investigate whether this dependency is due to pharmacokinetic and/or pharmacodynamic factors. The effect on two cell lines, MDA-MB-231 (breast cancer) and CCRF-CEM (leukaemia) were studied after CHS 828 was administered orally as a single dose or in a 5-day schedule, at different total dose levels. The 5-day schedules were associated with greater effects on both cell lines compared with single doses. A one-compartment pharmacokinetic model, with a half-life of 2.3h and a consecutive zero- and first-order process to describe dissolution and absorption, fit the concentration data. Pharmacokinetics were dose-dependent, as the fraction absorbed decreased with increasing dose. Clearance increased with accumulative exposure. Twenty hours after administration, concentrations started to increase again, probably due to coprophagy. Pharmacokinetic-pharmacodynamic models characterized the cell growth and cell kill over time and showed that schedule-dependent antitumour effects were present also when the dose-dependent pharmacokinetics were accounted for. The prolonged schedules of CHS 828 were therefore associated with greater antitumour effects than single doses of the same total exposure.

Physiologically based pharmacokinetic modeling of glycyrrhizic acid, a compound subject to presystemic metabolism and enterohepatic cycling

Glycyrrhizic acid is currently of clinical interest for treatment of chronic hepatitis. It is also applied as a sweetener in food products and chewing tobacco. In some highly exposed subgroups of the population, serious side effects such as hypertension and electrolyte disturbances have been reported. In order to analyze the health risks of exposure to this compound, the kinetics of glycyrrhizic acid and its active metabolites were evaluated quantitatively. Glycyrrhizic acid and its metabolites are subject to complex kinetic processes, including enterohepatic cycling and presystemic metabolism. In humans, detailed information on these processes is often difficult to obtain. Therefore, a model was developed that describes the systemic and gastrointestinal tract kinetics of glycyrrhizic acid and its active metabolite glycyrrhetic acid in rats. Due to the physiologically based structure of the model, data from earlier in vitro and in vivo studies on absorption, enterohepatic cycling, and presystemic metabolism could be incorporated directly. The model demonstrates that glycyrrhizic acid and metabolites are transported efficiently from plasma to the bile, possibly by the hepatic transfer protein 3-alpha-hydroxysteroid dehydrogenase. Bacterial hydrolysis of the biliary excreted metabolites following reuptake of glycyrrhetic acid causes the observed delay in the terminal plasma clearance of glycyrrhetic acid. These mechanistic findings, derived from analysis of experimental data through physiologically based pharmacokinetic modeling, can eventually be used for a quantitative health risk assessment of human exposure to glycyrrhizic acid containing products.

Percutaneous absorption and disposition of [14C]chlordecone in young and adult female rats

The objective of this study was to evaluate the effect of age and dosage on percutaneous absorption and disposition of [14C]chlordecone (Kepone) and to describe results using a physiological based pharmacokinetic (PBPK) model. Female Fischer 344 rats 33 and 82 days old were used as the young and adult animal models, respectively, and were studied over a 10-fold dose range. [14C]Chlordecone (0.286 micromol/cm2) was applied to dorsal skin (2. 3% BSA) and radioactivity was quantified in selected tissues and excreta up to 120 h. Absorption and disposition were also determined at three dose levels up to 2.68 micromol/cm2; fraction absorbed decreased as dose increased. In vitro percutaneous absorption was measured by static and flow-through methods; these yielded similar penetration rates, which were lower than those obtained in vivo. In vivo percutaneous absorption over 120 h was 14.4+/-0.99 and 14.2+/-1. 5% dose in young and adults, respectively. Organ and tissue content increased over time (carcass>liver>kidney), indicating prolonged absorption. Statistical differences between young and old were found for liver, skin, and urine, but not for absorption. Excretion occurred primarily in feces, but also in urine. A biophysically based percutaneous model was fitted to both young and adult in vivo absorption data. This was embedded in a whole body PBPK model which, upon optimization with SAAM II, estimated apparent tissue partition coefficients, urinary and fecal excretion rates, and parameters characterizing hepatic nonlinear uptake of bound chlordecone. The model reasonably predicted tissue chlordecone content at higher doses, when decreased absorption was accounted for.

Physiologically based pharmacokinetic (PB-PK) models in the study of the disposition and biological effects of xenobiotics and drugs

Physiologically based pharmacokinetic (PB-PK) models have been used to study the mechanisms of disposition of drugs and xenobiotics for almost 70 years. Their widespread application in toxicology began 15 years ago with models for polychlorinated biphenyls and other persistent lipophilic compounds. Quantitative applications of PB-PK moels in carcinogen risk assessment date to the development of a number of PB-PK models for dichloromethane in the mid 1980s. The expanding use of these models is primarily related to their ability to make more accurate predictions of target tissue dose for different exposure situations in different animal species, including humans, and to evaluate quantitatively the mechanisms of disposition of chemicals within the body. This paper discusses contemporary uses of PB-PK modeling in the context of risk assessment with xenobiotics and of safety assessment with drugs.

ATSDR evaluation of health effects of chemicals. II. Mirex and chlordecone: health effects, toxicokinetics, human exposure, and environmental fate

This document provides public health officials, physicians, toxicologists, and other interested individuals and groups with an overall perspective of the toxicology of mirex and chlordecone. It contains descriptions and evaluations of toxicological studies and epidemiological investigations and provides conclusions, where possible, on the relevance of toxicity and toxicokinetic data to public health. Additional substances will be profiled in a series of manuscripts to follow.

Development of physiologically based pharmacokinetic and physiologically based pharmacodynamic models for applications in toxicology and risk assessment

Pharmacokinetics (PK) involves the study of the rates of absorption, distribution, excretion, and biotransformation of chemicals and their metabolites. PK models can be used to reconstruct extensive time-course data sets based on a small number of kinetic parameters. These models can be used to predict the results of new experiments and integrate studies on kinetics, disposition and metabolism in various animal species [1]. The 2 main approaches that have been pursued in developing PK models are: (1) data-based compartmental modeling; and (2) physiologically based compartmental modeling. Data-based models rely on the collection of time-course concentration data and fitting these data with mathematical models. Compartments in these models do not necessarily reflect the anatomy and physiology of the animal, and the kinetic constants derived from these models do not have obvious physiological or biochemical counterparts. In physiologically based pharmacokinetic (PBPK) models, compartments correspond more closely to actual anatomical structures, defined with respect to their volumes, blood flows, chemical binding (partitioning) characteristics, and ability to metabolize or excrete the compounds of interest. Because the kinetic parameters of these models reflect tissue blood flows, partitioning, and biochemical constants, these models are more readily scaled from one animal species to another [2]. PBPK models have been used to understand the disposition of chemicals in the body for almost 70 years. Their more widespread application in toxicology dates back only 15 years or so to models developed for polychlorinated biphenyls and other persistent lipophilic compounds. Quantitative applications of PBPK models in risk assessment date to the development of a number of PBPK models for methylene chloride in the mid 1980s. The burgeoning use of PBPK models in toxicology research and chemical risk assessment today is primarily related to their ability to make more accurate predictions of target tissue dose for different exposure situations in different animal species, including humans. This overview includes a discussion of the development of these PBPK models in toxicology and speculates about future applications of PBPK and physiologically based pharmacodynamic (PBPD) models in chemical risk assessment.

Physiologically based pharmacokinetic and pharmacodynamic modeling in health risk assessment and characterization of hazardous substances

Recent advances in physiologically based pharmacokinetic and pharmacodynamic (PBPK/PD) modeling have introduced novel approaches for evaluating toxicological problems. Because PBPK models are amenable to extrapolation of tissue dosimetry, they are increasingly being applied to chemical risk assessment. A comprehensive listing of PBPK/PD models for environmental chemicals developed to date is referenced. Salient applications of PBPK/PD modeling to health risk assessments and characterization of hazardous substances are illustrated with examples.

Disposition of phenol in rat after oral, dermal, intravenous, and intratracheal administration

The absorption and elimination of [14C]-phenol (63.5 nmol) after oral, dermal, intratracheal, or intravenous administration in rat was rapid and extensive. Urinary elimination of radioactivity predominated, with a range of 75-95% of the dose detected in urine by 72 h post-exposure. Washing the dermal site 72 h post-exposure removed 14% of the dose. Two per cent of the dose was detected in the skin. The urinary metabolites at 4 and 8 h after administration by the four routes included phenyl sulphate and lower amounts of phenyl glucuronide. Phenol was poorly retained in the body after administration by the four routes. Phenol remaining in the body was widely distributed, with accumulation primarily in the liver, lung, and kidney.

Physiologically-based pharmacokinetic modeling and bioactivation of xenobiotics

This paper describes the development and implementation of physiologically-based pharmacokinetic (PB-Pk) models to examine the disposition of xenobiotics and their bioactivation. In a PB-Pk model, the structure of the model is based, to as great extent as practicable, on the actual physiological and biochemical structure of the animal system being described. This paper provides an overview of the PB-Pk modeling approach using a series of models as examples. PB-Pk models for styrene and the dihalomethanes are discussed in relation to their ability to predict the kinetics of uptake, distribution, metabolism (bioactivation), and elimination in both rodents and humans. Three models are discussed which demonstrate the process of describing increasing complexity in bioactivation with reference to saturation of metabolism (methylene chloride), suicide enzyme inactivation (trans-1,2-dichloroethylene), and glutathione depletion (allyl chloride). Experimental studies to quantify these particular examples of non-linear kinetics were conducted by closed chamber gas uptake techniques. All of these behaviors can be quantitatively expressed within the framework of a PB-Pk model.

Absorption of methylmercury from hair ingested by rats

Hair taken from rats dosed with 203Hg-labeled methylmercury was fed to previously untreated rats in order to determine if the organomercurial was available for release from the hair matrix within the gut lumen and for subsequent systemic absorption. Cumulative fecal excretion data were consistent with an absorption of about 80% of the ingested methylmercury. The relative amounts of methylmercury and of its metabolite, inorganic mercury, in the feces indicated that the percentage of the parent compound released from hair within the intestine equaled or exceeded the estimated bioavailability. Radioactivity in tissues of animals killed 42 hr following hair consumption confirmed that mercury absorption had occurred.

Development and utilization of physiologically based pharmacokinetic models for toxicological applications

Recent advances in physiologically based pharmacokinetic (PB-PK) modeling have introduced novel approaches for evaluating toxicological problems. Because PB-PK models are amenable to extrapolation of tissue dosimetry, they are increasingly being applied to chemical risk assessment. This paper reviews the development of PB-PK modeling for toxicological applications. It briefly compares and contrasts the fundamental differences between conventional compartmental analysis and PB-PK modeling. The theory and principles, data requirements and the methodologies to obtain them, and the steps to construct PB-PK models are described. A comprehensive listing of PB-PK models for environmental chemicals developed to date is referenced. Salient applications of PB-PK modeling to toxicological problems are illustrated with examples. Finally, the uncertainties and limitations in PB-PK modeling are also discussed.

A physiologically based pharmacokinetic model for 2,3,7,8-tetrachlorodibenzo-p-dioxin in C57BL/6J and DBA/2J mice

A five-compartment physiologically based pharmacokinetic (PB-PK) model was developed to describe the time course of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the tissues of both C57BL/6J and DBA/2J mice. The PB-PK model included binding in blood and two hepatic binding sites, one in the cytosol and the other in the microsomes. First-order metabolism occurred in the liver. Model simulations were compared to literature results for the disposition of a single intraperitoneal dose of 10 micrograms/kg of [3H]TCDD, reported by Gasiewicz et al. [Drug Metab. Dispos. 11 (1983) 397-403]. In contrast to previous speculation, the greater accumulation of TCDD in the liver of the C57BL/6J mouse, as compared to the DBA/2J mouse, was not attributable to the higher fat content in the DBA/2J mouse. Instead, the disposition of TCDD in these mice was more dependent on the affinity of the microsomal binding proteins than on fat content. The microsomal dissociation constant in the C57BL/6J mouse estimated by the PB-PK model was about one-third its value in the DBA/2J mouse (20 versus 75 nM), i.e. there is more avid microsomal binding in the liver of the C57BL/6J mouse. In the concentration range covered in these time-course studies, the cytosolic receptor, with its low capacity and very high affinity binding characteristics, does not play a major role in determining the overall tissue distribution pattern. The concentration and affinity of the microsomal binding protein in the liver appear to be primarily responsible for explaining the differences in the liver/fat concentration ratios between various strains and species of laboratory animals.

Dermal penetration of carbofuran in young and adult Fischer 344 rats

Dermal penetration of carbofuran was determined in young (33 d) and adult (82 d) female Fischer 344 rats employing in vivo and in vitro methods. In vivo dermal penetration at 120 h was 43% for young and 18% for adult rats. The half-time for carbofuran skin penetration (in vivo) was 128 h for the young and 400 h for the adults. The young to adult ratio of dermal penetration was greater than 1 at all time points (average 2.9) and had a maximum of 4.2 at 24 h. Cumulative urinary excretion approached about 95% of the absorbed dose in both the young and adult animals at 120 h. Whole-body retention was slightly higher in adults. Kidney showed the highest tissue-to-blood concentration ratio (4.6 in adult, 2.3 in young). The ratio for the carcass was 2.8 in the adult and 2.4 in the young. The urine/blood concentration ratio was high, 435 in the adult and 573 in the young. The feces/blood ratio was 44 in the adult and 65 in the young. Skin absorption by the in vitro continuous-flow system was 41% for the young and 11% for the adult at 72 h, compared to 36% and 13% by the in vivo method. The static in vitro method gave consistently lower skin penetration values of 12% for the young and 8.8% for the adult. Differences in the kinetics of retention and excretion were observed between the young and adult animals.

Extravascular transport in normal and tumor tissues

The transport characteristics of the normal and tumor tissue extravascular space provide the basis for the determination of the optimal dosage and schedule regimes of various pharmacological agents in detection and treatment of cancer. In order for the drug to reach the cellular space where most therapeutic action takes place, several transport steps must first occur: (1) tissue perfusion; (2) permeation across the capillary wall; (3) transport through interstitial space; and (4) transport across the cell membrane. Any of these steps including intracellular events such as metabolism can be the rate-limiting step to uptake of the drug, and these rate-limiting steps may be different in normal and tumor tissues. This review examines these transport limitations, first from an experimental point of view and then from a modeling point of view. Various types of experimental tumor models which have been used in animals to represent human tumors are discussed. Then, mathematical models of extravascular transport are discussed from the prespective of two approaches: compartmental and distributed. Compartmental models lump one or more sections of a tissue or body into a "compartment" to describe the time course of disposition of a substance. These models contain "effective" parameters which represent the entire compartment. Distributed models consider the structural and morphological aspects of the tissue to determine the transport properties of that tissue. These distributed models describe both the temporal and spatial distribution of a substance in tissues. Each of these modeling techniques is described in detail with applications for cancer detection and treatment in mind.

Risk assessment extrapolations and physiological modeling

The process of assessing the risk associated with human exposure to environmental chemicals inevitably relies on a number of assumptions, estimates and rationalizations. One of the more challenging aspects of risk assessment involves the need to extrapolate beyond the range of conditions used in experimental animal studies to predict anticipated human risks. The most obvious extrapolation required is that from the tested animal species to humans; but others are also generally required, including extrapolating from high dose to low dose, from one route of exposure to another and from one exposure timeframe to another. Several avenues are available for attempting these extrapolations, ranging from the assumption of strict correspondence of dose to the use of statistical correlations. One promising alternative for conducting more scientifically sound extrapolations is that of using physiologically based pharmacokinetic models that contain sufficient biological detail to allow pharmacokinetic behavior to be predicted for widely different exposure scenarios. In recent years, successful physiological models have been developed for a variety of volatile and nonvolatile chemicals, and their ability to perform the extrapolations needed in risk assessment has been demonstrated. Techniques for determining the necessary biochemical parameters are readily available, and the computational requirements are now within the scope of even a personal computer. In addition to providing a sound framework for extrapolation, the predictive power of a physiologically based pharmacokinetic model makes it a useful tool for more reliable dose selection before beginning large-scale studies, as well as for the retrospective analysis of experimental results.

The pharmacokinetics of chlortetracycline orally administered to turkeys: influence of citric acid and Pasteurella multocida infection

A physiologically based pharmacokinetic model was developed to describe the absorption and disposition of chlortetracyline (CTC) in the healthy and diseased (fowl cholera) turkey. The CTC was given (with and without citric acid) as an oral (15 mg/kg) or i.v. (1 mg/kg) dose. When minerals (0.3 g/L Ca2+, 0.1 g/L Mg2+) were dissolved in the bird's drinking water, the model indicated that the addition of citric acid (mass ratio of 10 citrate: 1 CTC) increased the fraction of dose absorbed from 0.06 to 0.16; once absorbed, the fractions of drug eliminated by renal excretion, biliary secretion, and chemical decomposition were 50, 46, and 4%, respectively. The presence of fowl cholera appeared to increase plasma levels by increasing the intestinal permeability and lowering the hepatic and/or renal clearance.

Pharmacokinetics and toxicity testing

The pharmacokinetic basis for the design of toxicity tests is discussed with reference to the absorption and clearance of drugs. The absorption and clearance of a wide range of drugs by laboratory animals and man has been examined and reviewed to provide a firm basis against which new drugs can be compared. Some pitfalls in either the empirical approach to toxicology or the incorrect interpretation of kinetic data are highlighted. An approach is outlined for the rational application of animal pharmacokinetic data in the assessment of the safety in man of a new therapeutic agent.

Spermotoxicity and tissue accumulation of chlordecone (Kepone) in male rats

Adult male rats were fed diets containing 0, 5, 15, and 30 ppm chlordecone for 90 d and then either bred to untreated females or sacrificed for terminal studies. Chlordecone residues in liver, fat, and serum were determined in the treated males. Reproductive performance was unaffected, and no histologic changes in the male sex organs could be attributed to chlordecone treatment. Reversible decreases in the motility and viability of epididymal spermatozoa and decreased sperm reserves in the cauda epididymidis were observed in rats fed 15 or 30 ppm. No effect on sperm morphology or on sperm concentration in epididymal fluid was detected. Chlordecone accumulation in tissues was linearly related to dietary levels, with the highest chlordecone concentration occurring in the liver.

Chlorinated paraffins: disposition of a highly chlorinated polychlorohexadecane in mice and quail

Uniformly 14C-labelled 1-chloro-polychlorohexadecane (PCHD) of high chlorine content (69% w/w) was given to Japanese quail and to C57Bl mice perorally (p.o.) and intravenously (i.v.). The degradation of PCHD to 14CO2, measured during 8 h, was found to be minute (about 1% of dose) in both species after either route of administration. In mice 66 and 43% of dose was eliminated in the feces during 96 h following p.o. and i.v. administration, respectively; the urinary excretion was about 3% in both cases. In quail, the combined fecal and urinary excretion during 96 h after p.o. administration was 58% of dose. The autoradiographic distribution following p.o. administration showed some general similarities between mice and quail; high radioactivities were present in bile, liver, kidney, and intestinal contents up to 24 h after administration. In addition, in quail high radioactivity was present in the hypophysis, retina, blood, and egg yolk. In mice strong accumulation and retention was observed in the corpora lutea up to 30 days after administration. A long time retention in fat occurred in both species.

Description and simulation of a physiological pharmacokinetic model for the metabolism and enterohepatic circulation of bile acids in man. Cholic acid in healthy man

A multicompartmental pharmacokinetic model based on physiological principles, experimental data, and the standard mathematical principles of compartmental analysis has been constructed that fully describes the metabolism and enterohepatic cycling in man of cholic acid, a major bile acid. The model features compartments and linear transfer coefficients. The compartments are aggregated into nine spaces based on physiological considerations (liver, gallbladder, bile ducts, jejunum, ileum, colon, portal blood sinusoidal blood, and general circulation). The transfer coefficients are also categorized according to function: flow, i.e., emptying of gallbladder or intestinal spaces, and circulation of the blood; biotransformation, i.e., conjugation, deconjugation, or dehydroxylation; and transport, i.e., active or passive transport. The model is made time dependent by introducing meals, which trigger discrete increases in gallbladder emptying and intestinal flow. Each space contains three compartments. For cholic acid, these are unconjugated cholic acid, cholylglycine, and cholyltaurine. The model was then used with all existing experimental data to simulate cholic acid metabolism in healthy man over a 24-h period. Satisfactory agreement was obtained between simulated and experimental results for serum bile acid levels, hepatic bile acid secretion, and bile acid secretion into the intestine. The model was also used to classify 16 clinical instances in which the enterohepatic circulation of bile acids is altered by drugs or disease. The model can be extended to describe completely the metabolism and enterohepatic circulation of any bile acids in man in health and digestive disease. The model should also be broadly applicable to the description of the pharmacokinetics of all other drugs whose metabolism is similar to that of bile acids, i.e., drugs for which there are tissue and bacterial biotransformations, enterohepatic cycling, and appreciable first-pass clearance.

Physiological model for the pharmacokinetics of 2,3,7,8-tetrachlorodibenzofuran in several species

A flow-limited physiological model was developed to describe the time course of 2,3,7,8-tetrachlorodibenzofuran (TCDF) in the blood and tissues of rats, mice, and monkeys. The liver showed the greatest tendency to concentrate the material with tissue-to-blood distribution coefficients ranging from 30 in the monkey to 130 in the mouse. TCDF was also concentrated in the fat with tissue-to-blood distribution coefficients between 25 and 40 in all species. TCDF was eliminated by metabolism followed by excretion primarily to the feces. Urinary excretion was a minor route of elimination in all species. Metabolism was modeled as a linear process occurring in the liver. Intrinsic metabolic clearances ranged from 0.45 ml/min/kg in the monkey to 2.8 ml/min/kg in one species of mice. Fecal excretion of TCDF-derived radioactivity can be simulated with a series of well-mixed compartments which receive input of metabolites in the bile.