Un modèle pharmacocinétique à base physiologique (PBPK) d’exposition par inhalation à l’éthanol a antérieurement été développé en se basant sur des données provenant d’une étude chez des volontaires exposés par inhalation à plus de 5000 ppm. Cependant, une incertitude persiste sur la capacité du modèle PBPK à prédire les niveaux d’éthanolémie pour des expositions à de faibles concentrations. Ces niveaux sont fréquemment rencontrés par une large partie de la population et des travailleurs suite à l’utilisation de produits tels que les vernis et les solutions hydroalcooliques (SHA). Il est ainsi nécessaire de vérifier la validité du modèle existant et de déterminer l’exposition interne à l’éthanol dans de telles conditions. Les objectifs du mémoire sont donc 1) de documenter les niveaux d’éthanolémie résultant de l’exposition par inhalation à de faibles concentrations d’éthanol (i.e., ≤ 1000 ppm) et de valider/raffiner le modèle PBPK existant pour ces concentrations ; et 2) de déterminer les concentrations d’éthanol atmosphérique provenant d’utilisation de SHA et de vernis et de prédire les niveaux d’éthanolémie découlant de leur utilisation. Les données toxicocinétiques récoltées chez des volontaires nous suggèrent qu’il est insuffisant de limiter au foie la clairance métabolique de l’éthanol lors d’exposition à de faibles niveaux d’éthanol, contrairement aux expositions à de plus forts niveaux. De plus, il a clairement été démontré qu’un effort physique léger (50 W) influençait à la hausse (2-3 fois) l’éthanolémie des volontaires exposés à 750 ppm. L’ajout au modèle PBPK d’une clairance métabolique de haute affinité et de faible capacité associée aux tissus richement perfusés a permis de simuler plus adéquatement la cinétique de l’éthanolémie pour des expositions à des concentrations inférieures à 1000 ppm. Des mesures de concentrations d’éthanol dans l’air inhalé générées lors d’utilisation de SHA et de vernis ont permis de simuler des expositions lors de l’utilisation de ces produits. Pour l’utilisation de 1,5 g et 3 g de SHA dans un local peu ventilé, des concentrations sanguines maximales (Cmax) de 0.383 et 0.366 mg.L-1 ont été respectivement simulées. Dans un local bien ventilé, les Cmax simulées étaient de 0.264 et 0.414 mg.L-1. Selon les simulations, une application de vernis résulterait en une Cmax respectivement de 0.719 mg.L-1 et de 0.729 mg.L-1, chez les hommes et femmes. Les Cmax sanguines d’éthanol estimées suites aux différentes simulations sont inférieures à la concentration toxique pour les humains (100 mg.L-1). Ainsi, de telles expositions ne semblent pas être un danger pour la santé. Les résultats de cette étude ont permis de mieux décrire et comprendre les processus d’élimination de l’éthanol à faibles doses et permettront de raffiner l’évaluation du risque associé à l’inhalation chronique de faibles niveaux d’éthanol pour la population, particulièrement chez les travailleurs. / A physiologically based pharmacokinetic model (PBPK) on inhalation exposure to ethanol has previously been developed based on data from an inhalation study in volunteers exposed to more than 5000 ppm. However, there remains uncertainty about the ability of the PBPK model to predict the blood levels of ethanol (BLE) for exposure to low concentrations. These levels are frequently encountered by a large part of the population and workers by using products such as varnishes and alcoholic solutions (HAS). It is therefore necessary to verify the validity of the existing model and determine the internal exposure to ethanol in such conditions. The objectives of this master’s thesis are 1) to document the BLE resulting from inhalation exposure to low concentrations of ethanol (i.e., ≤ 1000 ppm) and validate/refine the existing PBPK model for these concentrations, and 2) to determine the atmospheric concentrations of ethanol following the use of alcoholic solutions (HAS) and varnish as well as to predict the BLE resulting from their use. Toxicokinetic data collected from volunteers suggest that it is insufficient to limit metabolic clearance of ethanol to the liver during exposures to low levels of ethanol, unlike exposures to stronger levels. In addition, it was clearly demonstrated that light exercise (50W) increased (2-3 fold) the BLE in volunteers exposed to 750 ppm. An addition to the PBPK model of a metabolic clearance of high affinity and low capacity associated with richly perfused tissue was performed to simulate more accurately the toxicokinetic data from low and high ethanol exposure levels. Measurements of ethanol concentrations in inhaled air generated during the use of HAS and varnishes were used to simulate the exposure during the use of these products. The simulation for HAS, for 1.5 g and 3 g, gave a maximum blood concentration (Cmax) of 0.383 and 0.366 mg.L-1 respectively in a poorly ventilated room. In a well-ventilated room, the simulated Cmax for 1.5 g and 3 g of HAS were 0.264 and 0.414 mg.L-1, respectively. The simulation results from the use of ethanol-based varnish yielded a Cmax for men and women of 0.719 and 0.729 mg.L-1 respectively. The blood Cmax of ethanol previously listed for the various simulations are well below the toxic dose for humans (50 mg.L-1). Thus, such exposures do not seem to be a health hazard. The results of this study helped to better describe and understand the elimination of ethanol at low doses and refine the evaluation process associated with chronic inhalation of low levels of ethanol to the population risk, particularly in workers.

Un modèle pharmacocinétique à base physiologique (PBPK) d’exposition par inhalation à l’éthanol a antérieurement été développé en se basant sur des données provenant d’une étude chez des volontaires exposés par inhalation à plus de 5000 ppm. Cependant, une incertitude persiste sur la capacité du modèle PBPK à prédire les niveaux d’éthanolémie pour des expositions à de faibles concentrations. Ces niveaux sont fréquemment rencontrés par une large partie de la population et des travailleurs suite à l’utilisation de produits tels que les vernis et les solutions hydroalcooliques (SHA). Il est ainsi nécessaire de vérifier la validité du modèle existant et de déterminer l’exposition interne à l’éthanol dans de telles conditions. Les objectifs du mémoire sont donc 1) de documenter les niveaux d’éthanolémie résultant de l’exposition par inhalation à de faibles concentrations d’éthanol (i.e., ≤ 1000 ppm) et de valider/raffiner le modèle PBPK existant pour ces concentrations ; et 2) de déterminer les concentrations d’éthanol atmosphérique provenant d’utilisation de SHA et de vernis et de prédire les niveaux d’éthanolémie découlant de leur utilisation. Les données toxicocinétiques récoltées chez des volontaires nous suggèrent qu’il est insuffisant de limiter au foie la clairance métabolique de l’éthanol lors d’exposition à de faibles niveaux d’éthanol, contrairement aux expositions à de plus forts niveaux. De plus, il a clairement été démontré qu’un effort physique léger (50 W) influençait à la hausse (2-3 fois) l’éthanolémie des volontaires exposés à 750 ppm. L’ajout au modèle PBPK d’une clairance métabolique de haute affinité et de faible capacité associée aux tissus richement perfusés a permis de simuler plus adéquatement la cinétique de l’éthanolémie pour des expositions à des concentrations inférieures à 1000 ppm. Des mesures de concentrations d’éthanol dans l’air inhalé générées lors d’utilisation de SHA et de vernis ont permis de simuler des expositions lors de l’utilisation de ces produits. Pour l’utilisation de 1,5 g et 3 g de SHA dans un local peu ventilé, des concentrations sanguines maximales (Cmax) de 0.383 et 0.366 mg.L-1 ont été respectivement simulées. Dans un local bien ventilé, les Cmax simulées étaient de 0.264 et 0.414 mg.L-1. Selon les simulations, une application de vernis résulterait en une Cmax respectivement de 0.719 mg.L-1 et de 0.729 mg.L-1, chez les hommes et femmes. Les Cmax sanguines d’éthanol estimées suites aux différentes simulations sont inférieures à la concentration toxique pour les humains (100 mg.L-1). Ainsi, de telles expositions ne semblent pas être un danger pour la santé. Les résultats de cette étude ont permis de mieux décrire et comprendre les processus d’élimination de l’éthanol à faibles doses et permettront de raffiner l’évaluation du risque associé à l’inhalation chronique de faibles niveaux d’éthanol pour la population, particulièrement chez les travailleurs. / A physiologically based pharmacokinetic model (PBPK) on inhalation exposure to ethanol has previously been developed based on data from an inhalation study in volunteers exposed to more than 5000 ppm. However, there remains uncertainty about the ability of the PBPK model to predict the blood levels of ethanol (BLE) for exposure to low concentrations. These levels are frequently encountered by a large part of the population and workers by using products such as varnishes and alcoholic solutions (HAS). It is therefore necessary to verify the validity of the existing model and determine the internal exposure to ethanol in such conditions. The objectives of this master’s thesis are 1) to document the BLE resulting from inhalation exposure to low concentrations of ethanol (i.e., ≤ 1000 ppm) and validate/refine the existing PBPK model for these concentrations, and 2) to determine the atmospheric concentrations of ethanol following the use of alcoholic solutions (HAS) and varnish as well as to predict the BLE resulting from their use. Toxicokinetic data collected from volunteers suggest that it is insufficient to limit metabolic clearance of ethanol to the liver during exposures to low levels of ethanol, unlike exposures to stronger levels. In addition, it was clearly demonstrated that light exercise (50W) increased (2-3 fold) the BLE in volunteers exposed to 750 ppm. An addition to the PBPK model of a metabolic clearance of high affinity and low capacity associated with richly perfused tissue was performed to simulate more accurately the toxicokinetic data from low and high ethanol exposure levels. Measurements of ethanol concentrations in inhaled air generated during the use of HAS and varnishes were used to simulate the exposure during the use of these products. The simulation for HAS, for 1.5 g and 3 g, gave a maximum blood concentration (Cmax) of 0.383 and 0.366 mg.L-1 respectively in a poorly ventilated room. In a well-ventilated room, the simulated Cmax for 1.5 g and 3 g of HAS were 0.264 and 0.414 mg.L-1, respectively. The simulation results from the use of ethanol-based varnish yielded a Cmax for men and women of 0.719 and 0.729 mg.L-1 respectively. The blood Cmax of ethanol previously listed for the various simulations are well below the toxic dose for humans (50 mg.L-1). Thus, such exposures do not seem to be a health hazard. The results of this study helped to better describe and understand the elimination of ethanol at low doses and refine the evaluation process associated with chronic inhalation of low levels of ethanol to the population risk, particularly in workers.

Les pyréthrinoïdes sont des insecticides auxquels la population est quotidiennement exposée. Le composé parent est suspecté d’induire des perturbations neuronales et hormonales chez l’homme. Au sein de cette famille, la perméthrine (mélange d’isomère cis et trans) est le composé le plus utilisé dans le traitement des intérieurs de maison. Dans ce travail de thèse, nous proposons de développer un modèle PBPK pour la perméthrine et certains de ses métabolites urinaires, utilisés comme biomarqueurs d’exposition, et d’évaluer les interactions métaboliques des deux isomères. Trois étapes ont été suivies. Une méthode analytique par GC-MS/MS a été développée pour doser simultanément les composés dans les différentes matrices. Un modèle PBPK de la perméthrine chez le rat a été associé à un modèles PBPK réduit du DCCA et empirique du 4’-OH-PBA et du 3-PBA. Les paramètres toxicocinétiques de chaque composé ont été estimés dans un cadre Bayésien à partir d’expériences in vivo menées à la dose orale de 25 mg/kg de cis- ou trans-perméthrine chez le rat. Le modèle PBPK de la perméthrine a été vérifié sur des données de cinétique d’un mélange cis/trans. Le métabolisme hépatique de chaque composé a été quantifié chez l’homme sur des hépatocytes primaires dans des conditions optimales pour l’extrapolation in vitro-in vivo, en incubant les isomères séparément et en mélange. Ce travail de thèse souligne la possibilité d’établir un modèle PBPK générique pour les pyréthrinoïdes. L’absence d’interaction entre les isomères au niveau in vitro et lors de la vérification du modèle PBPK de la perméthrine pourrait simplifier la caractérisation de l’exposition à un mélange de pyréthrinoïdes. / Population is largely exposed to pyrethroids, an insecticide family. The parent compound is suspected to induce neuronal and hormonal modifications in humans. Among this family, permethrin, a mixture of isomers cis/trans, is mainly used in house tratments. In this PhD project, we developed a PBK model of permethrin and some urinary metabolites uses as biomarkers of exposure. The matabolic interactions between the two isomers were also evaluated. A three steps strategy was followed. An analytical method by GC-MS/MS was developed to measure these compounds simultaneously in the different matrices. A PBPK of permethrin in rat was associated to a reduced PBPK model of DCCA and a 2-compartment model of 4'-OH-PBA and 3-PBA. The toxicokinetics parameters of each compound were estimated in a Bayesian framework from in vivo experiments in rats orally dosed with 25 mg/kg of cis- or trans permethrin. The PBPK model of permethrin was validated on the kinetic data of a mixture of permethrin. The hepatic metabolism was quantified in humans in primary hepatocytes in optimal conditions for in vitro-in vivo extrapolation, by incubating the isomers separately and as a mixture. This work underlines that a general PBPK model for Type 2 pyrethroids can be considered for the parent compound The lack of interaction between isomers during in vitro experiments and the validation of the PBPK model of permethrin could simplify the characterization of the exposure to a mixture of pyrethroids.

Tuberculosis, the leading cause of death by a single infection disease caused by bacteria, requires long treatments and the bacteria are prone to develop drug resistance. Therefore, new efficient treatment regiments needs developing, which requires new tools for drug development. A major reason for discontinuance of a drug under development is undesired pharmacokinetic properties. Therefore, it is important to have early information of this, preferably the first time the drug is tested in animals. The first in vivo pharmacokinetic experiment is often done in mice and the only information present at this stage are often in vitro values and physicochemical properties. Physiological-based pharmacokinetic modelling can be used to extrapolate from in vitro to in vivo values. From this, the first in vivo pharmacokinetic experiment can be designed, often with the goal of reducing the amount of mice. This goal is one of the three R.s and it is called Reduction. To explore the Reduction of an experiment population pharmacokinetic modelling can be utilized via exploration of the imprecision, bias and probability of an informative experiment to evaluate if a design meets the goal of Reduction. In this report a recommendation of the first in vivo pharmacokinetic experiment is presented. This is based on in vitro values and physicochemical properties that are common in anti-tuberculosis drugs. If the probability of an informative experiment is critical, a terminal sampling of 40 mice is recommended. If imprecision and bias are necessary, zipper sampling of 10 mice is recommended.

Predicting drug concentrations in the blood and at the site of action is the hottest topic in pharmacokinetics (PK). In vitro-in vivo extrapolation (IVIVE) and physiological based pharmacokinetics (PBPK) models are two major PK prediction strategies. However, both IVIVE and PBPK models are considered as immature methodologies due to their poor predictability. The goal of the research is to investigate the discrepancies within IVIVE and PBPK predictions according to first-principles: convection, diffusion, metabolism, and carrier-mediated transport. In Chapter 2, non-permeability limited hepatic elimination under perfusion steady state is examined. The well-stirred model is re-derived from the convection-dispersion-elimination equation when both dispersion and concentration gradient are ignored and re-named as the zero-gradient model. Pang and Rowland’s lidocaine data are re-analyzed. Their data analysis was based on an unfair comparison of the zero-gradient and parallel- tube models at two different efficiency number ranges. The interference of sensitivity greatly biased the comparison. I also show that both theoretical discussions and experimental results indicate that apparent intrinsic clearance and intrinsic clearance could be affected by blood flow and protein binding. In Chapter 3, I discuss permeability limited hepatic elimination under perfusion steady state. Permeability limited elimination is classified to diffusion dominated, carrier-mediated transport mediated, and mixed effects based on drug passage mechanisms. Each of these three drug passage classes is sub-divided to sink condition and finite volume condition based on the boundary conditions of drug passage. In Chapter 4, the discrepancies within IVIVE for both non-permeability limited and permeability limited drugs are explored. The deficiencies in assay design and data analysis of common in vitro metabolism assays are investigated. The scaling/converting equations for both non-permeability limited and permeability limited drugs are derived. In Chapter 5, I focus on transient PK models. Numerical analysis using finite difference and finite volume methods are introduced into the derivation and discussion of transient PBPK models. In addition, the use of partition coefficient in the non-eliminating tissue/organ models is discussed.

Cotutelle Québec-France. J'ai effectué une cotutelle de thèse entre l'Université de Montréal (Québec) et l'Université de Poitiers (France). / Les dérivés chlorés du Bisphénol A (ClxBPA) sont des polluants émergents qui possèdent des effets perturbateurs endocriniens. Lors du traitement de l’eau potable par chloration, le Bisphénol A (BPA) présent dans l’environnement peut réagir avec les molécules de chlore pour former des dérivés chlorés (ClBPA, Cl2BPA, Cl3BPA et Cl4BPA) ou ClxBPA. Ils sont présents dans divers milieux aquatiques tels que eaux usées et l’eau potable. Ces polluants émergents ont également été retrouvés chez l’humain, dans l’urine, le colostrum et le tissu placentaire. Dans une étude transversale, la présence de concentrations urinaires élevées de ClxBPA chez l’humain a été positivement associée au diabète de type 2. Les ClxBPA ont aussi été associés à l’obésité et à l’infarctus du myocarde. Dans la littérature, il n’existait que très peu de données sur la toxicocinétique des ClxBPA chez l’animal ou chez l’humain. Cette recherche doctorale vise à évaluer le risque lié à ces polluants émergents en déterminant les constantes métaboliques des ClxBPA, puis en élaborant une méthode analytique des métabolites du 3,3’-Cl2BPA par HPLC-MS/MS pour finalement valider un modèle pharmacocinétique à base physiologique (PBPK) chez l’animal. Dans un premier temps, les constantes métaboliques (Km, Vmax et la clairance intrinsèque) ont été déterminées à l’aide d’expérience in vitro avec des hépatocytes de rats et d’humain. Les essais ont révélé que les constantes métaboliques des ClxBPA peuvent varier considérablement en fonction des substances et des espèces. Ces expériences in vitro ont montré que la chloration avait un impact sur la clairance intrinsèque hépatique des ClxBPA chez les rats et les humains. Deuxièmement, nous avons développé une méthode analytique pour les métabolites du 3,3’-Cl2BPA par HPLC-MS/MS dans le plasma à l’Université de Poitiers. Nous avons pu valider cette méthode avec des échantillons de rats et d’humain. Les résultats ont montré que chez le rat Sprague-Dawley après administration i.v., le 3,3’-Cl2BPA-glucuronide est largement présent par rapport au 3,3’-Cl2BPA-sulfate. Pour l'humain, seul le 3,3’-Cl2BPA-G-d12 a été quantifié. Finalement, nous avons utilisé des méthodes in vitro (dialyse à l’équilibre) et in silico pour les paramètres physico-chimiques de chaque ClxBPA. Enfin, nous avons construit des modèles PBPK afin de simuler la pharmacocinétique i.v. chez le rat Sprague-Dawley pour chaque dérivé chloré. Deux modèles PBPK ont été développés : un avec le ClBPA, le Cl2BPA et le Cl3BPA versus le Cl4BPA avec un modèle à diffusion limitée. Il a été validé par une expérience in vivo sur 80 rats Sprague-Dawley. Le modèle calibré a prédit les concentrations mesurées des ClxBPA dans le plasma, le cerveau et les muscles après l’administration de 4 et 40 mg/kg pour ClBPA et Cl2BPA; 0,4 et 4 mg/kg pour Cl3BPA et Cl4BPA. Ce projet doctoral a contribué à 1) déterminer les constantes métaboliques (Km, Vmax, Clairance intrinsèque) des ClxBPA, 2) de développer et valider une méthode analytique par HPLC-MS/MS des métabolites du Cl2BPA dans le plasma animal et humain et 3) de valider deux modèles PBPK chez le rat afin de connaitre la distribution plasmatique et tissulaire des ClxBPA. / Chlorinated derivatives of Bisphenol A (ClxBPA) are emerging pollutants with endocrine disrupting effects. During the treatment of drinking water by chlorination, Bisphenol A (BPA) present in the environment can react with chlorine molecules to form chlorinated derivatives (ClBPA, Cl2BPA, Cl3BPA and Cl4BPA) or ClxBPA. They are present in various aquatic environments such as wastewater and drinking water. These emerging pollutants have also been found in humans, in urine, colostrum and placental tissue. In a cross-sectional study, high urinary ClxBPA levels in humans were positively associated with type 2 diabetes. ClxBPA has also been associated with obesity and myocardial infarction. In the literature, there was very limited data on the toxicokinetics of ClxBPA in animals or in humans. This doctoral research aims to assess the risk related to these emerging pollutants by determining the metabolic constants of ClxBPA and then developing an analytical method for 3,3'-Cl2BPA metabolites by HPLC-MS/MS to validate a physiologically based pharmacokinetic (PBPK) model in animals. First, metabolic constants (Km, Vmax, and intrinsic clearance) were determined using in vitro experiments with rat and human hepatocytes. The tests revealed that the metabolic constants of ClxBPA can vary considerably between substances and species. These in vitro experiments showed that chlorination impacted the intrinsic hepatic clearance of ClxBPA in rats and humans. Second, we developed an analytical method for 3,3'-Cl2BPA metabolites by HPLC-MS/MS in plasma at the University of Poitiers. We were able to validate this method with rat and human samples. The results demonstrated that in Sprague-Dawley rats after an i.v. administration, 3,3'-Cl2BPA-glucuronide is largely present compared to 3,3'-Cl2BPA-sulfate. For humans, only 3,3'-Cl2BPA-G-d12 was quantified. Finally, we used in vitro (equilibrium dialysis) and in silico methods for the physicochemical parameters of each ClxBPA. Finally, we constructed PBPK models to simulate the i.v. pharmacokinetics in Sprague-Dawley rats for each chlorinated derivative. Two PBPK models were developed: one with ClBPA, Cl2BPA and Cl3BPA versus Cl4BPA with a diffusion- limited model. It was validated by an in vivo experiment on 80 Sprague-Dawley rats. The calibrated model predicted measured ClxBPA concentrations in plasma, brain, and muscle after administration of 4 and 40 mg/kg for ClBPA and Cl2BPA: 0.4 and 4 mg/kg for Cl3BPA and Cl4BPA. This doctoral project contributed to 1) determine the metabolic constants (Km, Vmax, Intrinsic Clearance) of ClxBPA, 2) develop and validate an analytical method by HPLC-MS/MS of Cl2BPA metabolites in animal and human plasma and 3) validate two PBPK models in rats to understand the plasma and tissue distribution of ClxBPA.

Nuclear receptors play significant roles in the regulation of transporters and enzymes to balance the level of endogenous molecules and to protect the body from foreign molecules. The vitamin D receptor (VDR) and its natural ligand, 1alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3], was shown to upregulate rat ileal apical sodium dependent bile acid transporter (Asbt) to increase the reclamation of bile acids, ligands of the farnesoid X receptor (FXR). FXR is considered to be an important, negative regulator of the cholesterol metabolizing enzyme, Cyp7a1, which metabolizes cholesterol to bile acids in the liver. In rats, decreased Cyp7a1 and increased P-glycoprotein/multidrug resistance protein 1 (P-gp/Mdr1) expressions pursuant to 1,25(OH)2D3 treatment was viewed as FXR effects in which hepatic VDR protein is poorly expressed. In contrast, changes in rat intestinal and renal transporters such as multidrug resistance associated proteins (Mrp2, Mrp3, and Mrp4), Asbt, and P-gp after administration of 1,25(OH)2D3 were attributed directly as VDR effects due to higher VDR levels expressed in these tissues. Higher VDR expressions were found among mouse hepatocytes compared to those in rats. Hence, fxr(-/-) and fxr(+/+) mouse models were used to discriminate between VDR vs. FXR effects in murine livers. Hepatic Cyp7a1 in mice was found to be upregulated with 1,25(OH)2D3 treatment, via the derepression of the short heterodimer partner (SHP). Putative VDREs, identified in mouse and human SHP promoters, were responsible for the inhibitory effect on SHP. The increase in hepatic Cyp7a1 expression and decreased plasma and liver cholesterol were observed in mice prefed with a Western diet. A strong correlation was found between tissue Cyp7a1 and P-gp changes and 1,25(OH)2D3 plasma and tissue concentrations, confirming that VDR plays an important role in the disposition of xenobiotics and cholesterol metabolism. Moreover, renal and brain Mdr1a/P-gp were found to be directly upregulated by the VDR in mice, and concomitantly, increased renal and brain secretion of digoxin, a P-gp substrate, in vivo. The important observations: the cholesterol lowering and increased brain P-gp efflux activity properties suggest that VDR is a therapeutic target for treatment of hypercholesterolemia and Alzheimer’s diseases, since beta amyloid, precursors of plague, are P-gp substrates.

Nuclear receptors play significant roles in the regulation of transporters and enzymes to balance the level of endogenous molecules and to protect the body from foreign molecules. The vitamin D receptor (VDR) and its natural ligand, 1alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3], was shown to upregulate rat ileal apical sodium dependent bile acid transporter (Asbt) to increase the reclamation of bile acids, ligands of the farnesoid X receptor (FXR). FXR is considered to be an important, negative regulator of the cholesterol metabolizing enzyme, Cyp7a1, which metabolizes cholesterol to bile acids in the liver. In rats, decreased Cyp7a1 and increased P-glycoprotein/multidrug resistance protein 1 (P-gp/Mdr1) expressions pursuant to 1,25(OH)2D3 treatment was viewed as FXR effects in which hepatic VDR protein is poorly expressed. In contrast, changes in rat intestinal and renal transporters such as multidrug resistance associated proteins (Mrp2, Mrp3, and Mrp4), Asbt, and P-gp after administration of 1,25(OH)2D3 were attributed directly as VDR effects due to higher VDR levels expressed in these tissues. Higher VDR expressions were found among mouse hepatocytes compared to those in rats. Hence, fxr(-/-) and fxr(+/+) mouse models were used to discriminate between VDR vs. FXR effects in murine livers. Hepatic Cyp7a1 in mice was found to be upregulated with 1,25(OH)2D3 treatment, via the derepression of the short heterodimer partner (SHP). Putative VDREs, identified in mouse and human SHP promoters, were responsible for the inhibitory effect on SHP. The increase in hepatic Cyp7a1 expression and decreased plasma and liver cholesterol were observed in mice prefed with a Western diet. A strong correlation was found between tissue Cyp7a1 and P-gp changes and 1,25(OH)2D3 plasma and tissue concentrations, confirming that VDR plays an important role in the disposition of xenobiotics and cholesterol metabolism. Moreover, renal and brain Mdr1a/P-gp were found to be directly upregulated by the VDR in mice, and concomitantly, increased renal and brain secretion of digoxin, a P-gp substrate, in vivo. The important observations: the cholesterol lowering and increased brain P-gp efflux activity properties suggest that VDR is a therapeutic target for treatment of hypercholesterolemia and Alzheimer’s diseases, since beta amyloid, precursors of plague, are P-gp substrates.

Kyoto University (京都大学) / 0048 / 新制・論文博士 / 博士(工学) / 乙第12491号 / 論工博第4045号 / 新制||工||1503(附属図書館) / 28241 / (主査)教授 小尻 利治, 教授 椎葉 充晴, 教授 堀 智晴 / 学位規則第4条第2項該当