Os transportadores de membrana do tipo ATP Binding Cassette (ABC) e solute carriers (SLC) regulam a homeostase intracelular de fármacos, modificando a biodisponibilidade e possivelmente a eficácia terapêutica. A variabilidade na resposta a hipolipemiantes, como as vastatinas, tem sido associada a vários fatores genéticos e ambientais. Com a finalidade de avaliarmos os mecanismos de regulação da expressão dos transportadores pela atorvastatina, a expressão de RNAm de transportadores ABC (ABCB1, ABCG2 e ABCC2) e SLC (SLCO1B1, SLCO2B1 e SLC22A1) foi avaliada por RT-PCRq em células mononucleares do sangue periférico (CMSP) de 18 indivíduos normolipidêmicos (NL) e 22 pacientes hipercolesterolêmicos (HC) tratados com atorvastatina (10mg/dia/4 semanas). A possível associação entre o polimorfismo ABCB1 C3435T e a expressão de RNAm também foi avaliada. Os estudos in vitro foram realizados com as células das linhagens HepG2 e Caco-2. Foram avaliados os efeitos da atorvastatina na ativação de fatores de transcrição (NF-kappaB, NF-Y, c-jun, SP-1 e PXR) por ensaio de mobilidade eletroforética retardada em gel de poliacrilamida (EMSA) e na meia-vida do RNAm do gene ABCB1 por RT-PCRq, e a expressão e atividade funcional da proteína ABCB1 por Western blot, imunohistoquimica e citometria de fluxo. A proteina ABCB1 foi localizada por imunohistoquimica na membrana apical do canalículo biliar das celulas HepG2 e na membrana apical das Caco-2. O tratamento das células HepG2 com atorvastatina causou redução da expressão de RNAm do gene ABCB1 e aumento na expressão dos genes ABCG2 e ABCC2. Esses efeitos foram dose e tempo dependentes. O tratamento com atorvastatina das células Caco-2 não modificou a expressão dos transportadores de efluxo após 30 a 120 min. Nas células HepG2, as concentrações de 10 e 20 M de atorvastatina causaram diminuição da expressão de ABCB1 (0 &#181;M: 1,00 ± 0,06; 10 &#181;M: 0,69 ± 0,25, p< 0,05; 20 &#181;M: 0,69 ± 0,06, p< 0,05). A atividade da ABCB1, avaliada pelo efluxo de Rh123, mostrou-se estar reduzida em 41% nas células HepG2, após tratamento com atorvastatina 20 &#181;M. Embora a diminuição da expressão do ABCB1 não tenha sido decorrente de uma menor ativação transcricional, avaliada indiretamente por EMSA, estudos de mecanismos de regulação pós-transcricionais, revelaram que a atorvastatina diminui a estabilidade de RNAm do gene ABCB1. Esse resultado parece estar de acordo com o ocorrido nas CMSP, já que o tratamento com atorvastatina diminuiu a expressão de RNAm do gene ABCB1 nos indivíduos HC. Essa modulação, no entanto não está associada à presença do polimorfismo ABCB1 C3435T. Em relação aos transportadores de captação, a expressão do SLC22A1 nas células Caco-2 diminui após tratamento com atorvastatina por 30 min e não foi modificada nas células HepG2. Já o gene SLCO2B1 encontrou-se muito aumentado após 24 h de tratamento nas células HepG2. Estudos in vivo nas CMSP, mostrou que a expressão de mRNA basal dos transportadores nos HC foi 10 vezes maior que nos NL e diminuiu após tratamento com atorvastatina nos HC. Com os resultados obtidos podemos sugerir que diferenças no efeito da atorvastatina nos tipos celulares podem ser em decorrência da expressão tecido-específica de fatores de transcrição. No modelo de hepatócito, HepG2, a atorvastatina é um inibidor do transporte mediado pela ABCB1 e é capaz de diminuir a síntese e a função da ABCB1, via aumento da degradação de RNAm do gene ABCB1. Em conseqüência ocorre uma redução do efluxo pelo sistema biliar, causando aumento da concentração intracelular. Ainda, podemos concluir que em CMSP o colesterol pode ser o responsável pela modulação dos genes dos transportadores de membrana e que isso pode implicar em diferenças na eficácia da atorvastatina. / Specific membrane transporters have a significant impact on drug absorption and disposition. Most of them belong to two super-families, ABC (ATP-binding cassette) and SLC (solute-linked carrier). Statins are important therapeutic agents in the management of hypercholesterolemia, and considerable inter-individual variation exists in response to its therapy. The effects of atorvastatin expression of efflux (ABCG2 and ABCC2) and uptake (SLCO1B1, SLCO2B1 and SLC22A1) drug transporters were investigated by qPCR in Caco-2 and HepG2 cell lines and in peripheral blood mononuclear cells (PBMCs) of eighteen normolipidemic (NL) and twenty two hypercholesterolemic (HC) individuals treated with atorvastatin (10mg/day/4 weeks). The possible involvement of ABCB1 C3435T polymorphism in ABCB1 mRNA expression was also evaluated. In vitro studies with the cell lines HepG2 and Caco-2 were also performed. The effect of atorvastatin on the activation of the promoter of ABCB1 by transcription factors (NF-kappaB, NF-Y, c-jun, SP-1, and PXR) was evaluated by electrophoretic mobility shift assay (EMSA), and ABCB1 mRNA half-life were measured by PCRq. The expression and functional activity of ABCB1 were investigated by Western blot, imunohistochemistry and flow cytometry. Immunohystochemical analysis revealed that ABCB1 is located at the apical membrane of the bile canaliculi in HepG2, and in apical membrane of Caco-2 cells. Atorvastatin treatment of HepG2 cells caused a decreased in ABCB1 and an increase in ABCC2 and ABCG2 transcript levels. These effects were time and dose-dependent. Treatment of Caco-2 cells did not present any differences in efflux transporters mRNA levels. Treatment of HepG2 cells with 10 and 20 M atorvastatin caused a reduction on ABCB1 expression (0 &#181;M: 1,00 ± 0,06; 10 &#181;M: 0,69 ± 0,25, p< 0,05; 20 &#181;M: 0,69 ± 0,06, p< 0,05), and a 41% decrease in ABCB1-mediated efflux of Rhodamine123 (p < 0.01). Although reduced ABCB1 mRNA expression was not due to any repressor protein suppressing ABCB1 promoter activation, mRNA stability studies revealed that mRNA stability of ABCB1 was markedly decreased by atorvastatin treatment (2h versus 7h for control). In agrrement with these results, in PBMCs of HC individuals, atorvastatin treatment also reduced ABCB1 mRNA expression. However, the down-regulation was not associated with the presence of 3435T allele. For the uptake transporters, atorvastatin decreased SLC22A1 transcript levels after 30min-treatment and it was not regulated in HepG2. On the other hand, SLCO2B1 was up-regulated after 24h-treatment of HepG2 cells. In vivo studies with PBMCs revealed that during hypercholesterolemia all the drug transporters analyzed were increased almost 10-fold (p< 0.05), and after atorvastatin therapy the efflux and uptake transporters transcript levels were all down-regulated. These findings suggest that atorvastatin exhibits differential effects on mRNA expression of drug transporters depending on the cell type, which may be related to tissue-specific expression of transcription factors. Atorvastatin leads to decreased ABCB1 function and synthesis in HepG2 cells by increasing degradation of ABCB1 mRNA. Therefore, inhibition of ABCB1 may reduce atorvastatin elimination via bile, increasing its cellular concentrations. We also may suggest that in PBMCs cholesterol modulates mRNA expression of drug transporters, and this may contribute to the variability of response to atorvastatin.

Le rein joue un rôle essentiel dans l’élimination des médicaments et de leurs métabolites, de ce fait il assure la défense de l'organisme contre de potentiels xénobiotiques toxiques. Particulièrement, les transporteurs des tubules proximaux rénaux qui ont un rôle dans la sécrétion tubulaire des médicaments. Ainsi, ils sont des déterminants important de la biodisponibilité des xénobiotiques dans l’organisme.Dans cette thèse nous nous sommes intéressés à l’implication des transporteurs rénaux humains hOAT1 et hOAT3 dans des interactions médicamenteuses moyennant des modèles in vitro. Après construction et validation des modèles d’études cellulaires HEK-hOAT1 et HEK-hOAT3, nous avons testé l’effet des inhibiteurs de la pompe à protons sur le transport du méthotrexate par les OATs ainsi que l’effet des antiviraux sur l’influx du tenofovir par ces mêmes transporteurs. Grâce à nos modèles cellulaires nous avons tenté d’expliquer in vitro de probables interactions médicamenteuses décrites en clinique. / The kidney plays an essential role in the elimination of drugs and their metabolites, thus it ensures the defense of the body against potential toxic xenobiotic. Particularly, the secretory transporters in the proximal tubule are major determinants of the disposition of xenobiotic in the body.In this thesis we investigated the involvement of human organic anions transporters hOAT1 and hOAT3 in drug drug interactions through study on in vitro cell models. After construction and validation of cells models studies HEK-hOAT1 and HEK-hOAT3, we tested the effect of proton pump inhibitors on methotrexate transport by OATs and the effect of antivirals on the influx of tenofovir by these two transporters. With our models we tried to explain in vitro probable drug interactions described in the clinic.

Biliary excretion is an important elimination route for many drugs and metabolites. For such compounds, it is important to know the extent of excretion and drug exposure in the bile, e.g., for the risk assessment of drug interactions, liver toxicity and the effects of genetic variants. In this thesis, duodenal aspiration of bile was performed in healthy volunteers and complemented with experiments in an in vivo model in pigs to increase the understanding of the intestinal and hepatobiliary disposition of two direct thrombin inhibitors. The compounds investigated, ximelagatran and AZD0837, are both prodrugs that require bioactivation to exert their pharmacological effect. Upon co-administration with erythromycin and ketoconazole, respectively, altered plasma exposure to ximelagatran and AZD0837 and their respective metabolites has been observed. The main objective of this thesis was to characterize the biliary excretion of the compounds, and investigate whether this elimination route explains the observed drug-drug interactions. High plasma-to-bile AUC ratios were observed, in particular for ximelagatran, its active metabolite melagatran, and AR-H067637, the active metabolite of AZD0837. These high ratios indicate the involvement of active transporters in the biliary excretion of the compounds, which is important since transporters constitute possible sites for drug interactions. The effects of erythromycin and ketoconazole on the plasma exposure of the prodrugs and metabolites were confirmed in both the pig and the clinical studies. The changes seen in plasma for ximelagatran and its metabolites were partly explained by reduced biliary clearance. Inhibited CYP3A4 metabolism likely caused the elevated plasma levels of AZD0837, whereas reduced biliary clearance was seen for AR-H067637 suggesting an effect on its excretion into bile. In summary, the studies led to mechanistic insights in the hepatobiliary disposition of ximelagatran and AZD0837, and demonstrate the value of combined clinical and animal studies for the investigation of the biliary drug excretion.

Thesis (Ph.D.). / Written for the Institute of Parasitology. Title from title page of PDF (viewed 2008/02/12). Includes bibliographical references.

Os transportadores de membrana do tipo ATP Binding Cassette (ABC) e solute carriers (SLC) regulam a homeostase intracelular de fármacos, modificando a biodisponibilidade e possivelmente a eficácia terapêutica. A variabilidade na resposta a hipolipemiantes, como as vastatinas, tem sido associada a vários fatores genéticos e ambientais. Com a finalidade de avaliarmos os mecanismos de regulação da expressão dos transportadores pela atorvastatina, a expressão de RNAm de transportadores ABC (ABCB1, ABCG2 e ABCC2) e SLC (SLCO1B1, SLCO2B1 e SLC22A1) foi avaliada por RT-PCRq em células mononucleares do sangue periférico (CMSP) de 18 indivíduos normolipidêmicos (NL) e 22 pacientes hipercolesterolêmicos (HC) tratados com atorvastatina (10mg/dia/4 semanas). A possível associação entre o polimorfismo ABCB1 C3435T e a expressão de RNAm também foi avaliada. Os estudos in vitro foram realizados com as células das linhagens HepG2 e Caco-2. Foram avaliados os efeitos da atorvastatina na ativação de fatores de transcrição (NF-kappaB, NF-Y, c-jun, SP-1 e PXR) por ensaio de mobilidade eletroforética retardada em gel de poliacrilamida (EMSA) e na meia-vida do RNAm do gene ABCB1 por RT-PCRq, e a expressão e atividade funcional da proteína ABCB1 por Western blot, imunohistoquimica e citometria de fluxo. A proteina ABCB1 foi localizada por imunohistoquimica na membrana apical do canalículo biliar das celulas HepG2 e na membrana apical das Caco-2. O tratamento das células HepG2 com atorvastatina causou redução da expressão de RNAm do gene ABCB1 e aumento na expressão dos genes ABCG2 e ABCC2. Esses efeitos foram dose e tempo dependentes. O tratamento com atorvastatina das células Caco-2 não modificou a expressão dos transportadores de efluxo após 30 a 120 min. Nas células HepG2, as concentrações de 10 e 20 M de atorvastatina causaram diminuição da expressão de ABCB1 (0 &#181;M: 1,00 ± 0,06; 10 &#181;M: 0,69 ± 0,25, p< 0,05; 20 &#181;M: 0,69 ± 0,06, p< 0,05). A atividade da ABCB1, avaliada pelo efluxo de Rh123, mostrou-se estar reduzida em 41% nas células HepG2, após tratamento com atorvastatina 20 &#181;M. Embora a diminuição da expressão do ABCB1 não tenha sido decorrente de uma menor ativação transcricional, avaliada indiretamente por EMSA, estudos de mecanismos de regulação pós-transcricionais, revelaram que a atorvastatina diminui a estabilidade de RNAm do gene ABCB1. Esse resultado parece estar de acordo com o ocorrido nas CMSP, já que o tratamento com atorvastatina diminuiu a expressão de RNAm do gene ABCB1 nos indivíduos HC. Essa modulação, no entanto não está associada à presença do polimorfismo ABCB1 C3435T. Em relação aos transportadores de captação, a expressão do SLC22A1 nas células Caco-2 diminui após tratamento com atorvastatina por 30 min e não foi modificada nas células HepG2. Já o gene SLCO2B1 encontrou-se muito aumentado após 24 h de tratamento nas células HepG2. Estudos in vivo nas CMSP, mostrou que a expressão de mRNA basal dos transportadores nos HC foi 10 vezes maior que nos NL e diminuiu após tratamento com atorvastatina nos HC. Com os resultados obtidos podemos sugerir que diferenças no efeito da atorvastatina nos tipos celulares podem ser em decorrência da expressão tecido-específica de fatores de transcrição. No modelo de hepatócito, HepG2, a atorvastatina é um inibidor do transporte mediado pela ABCB1 e é capaz de diminuir a síntese e a função da ABCB1, via aumento da degradação de RNAm do gene ABCB1. Em conseqüência ocorre uma redução do efluxo pelo sistema biliar, causando aumento da concentração intracelular. Ainda, podemos concluir que em CMSP o colesterol pode ser o responsável pela modulação dos genes dos transportadores de membrana e que isso pode implicar em diferenças na eficácia da atorvastatina. / Specific membrane transporters have a significant impact on drug absorption and disposition. Most of them belong to two super-families, ABC (ATP-binding cassette) and SLC (solute-linked carrier). Statins are important therapeutic agents in the management of hypercholesterolemia, and considerable inter-individual variation exists in response to its therapy. The effects of atorvastatin expression of efflux (ABCG2 and ABCC2) and uptake (SLCO1B1, SLCO2B1 and SLC22A1) drug transporters were investigated by qPCR in Caco-2 and HepG2 cell lines and in peripheral blood mononuclear cells (PBMCs) of eighteen normolipidemic (NL) and twenty two hypercholesterolemic (HC) individuals treated with atorvastatin (10mg/day/4 weeks). The possible involvement of ABCB1 C3435T polymorphism in ABCB1 mRNA expression was also evaluated. In vitro studies with the cell lines HepG2 and Caco-2 were also performed. The effect of atorvastatin on the activation of the promoter of ABCB1 by transcription factors (NF-kappaB, NF-Y, c-jun, SP-1, and PXR) was evaluated by electrophoretic mobility shift assay (EMSA), and ABCB1 mRNA half-life were measured by PCRq. The expression and functional activity of ABCB1 were investigated by Western blot, imunohistochemistry and flow cytometry. Immunohystochemical analysis revealed that ABCB1 is located at the apical membrane of the bile canaliculi in HepG2, and in apical membrane of Caco-2 cells. Atorvastatin treatment of HepG2 cells caused a decreased in ABCB1 and an increase in ABCC2 and ABCG2 transcript levels. These effects were time and dose-dependent. Treatment of Caco-2 cells did not present any differences in efflux transporters mRNA levels. Treatment of HepG2 cells with 10 and 20 M atorvastatin caused a reduction on ABCB1 expression (0 &#181;M: 1,00 ± 0,06; 10 &#181;M: 0,69 ± 0,25, p< 0,05; 20 &#181;M: 0,69 ± 0,06, p< 0,05), and a 41% decrease in ABCB1-mediated efflux of Rhodamine123 (p < 0.01). Although reduced ABCB1 mRNA expression was not due to any repressor protein suppressing ABCB1 promoter activation, mRNA stability studies revealed that mRNA stability of ABCB1 was markedly decreased by atorvastatin treatment (2h versus 7h for control). In agrrement with these results, in PBMCs of HC individuals, atorvastatin treatment also reduced ABCB1 mRNA expression. However, the down-regulation was not associated with the presence of 3435T allele. For the uptake transporters, atorvastatin decreased SLC22A1 transcript levels after 30min-treatment and it was not regulated in HepG2. On the other hand, SLCO2B1 was up-regulated after 24h-treatment of HepG2 cells. In vivo studies with PBMCs revealed that during hypercholesterolemia all the drug transporters analyzed were increased almost 10-fold (p< 0.05), and after atorvastatin therapy the efflux and uptake transporters transcript levels were all down-regulated. These findings suggest that atorvastatin exhibits differential effects on mRNA expression of drug transporters depending on the cell type, which may be related to tissue-specific expression of transcription factors. Atorvastatin leads to decreased ABCB1 function and synthesis in HepG2 cells by increasing degradation of ABCB1 mRNA. Therefore, inhibition of ABCB1 may reduce atorvastatin elimination via bile, increasing its cellular concentrations. We also may suggest that in PBMCs cholesterol modulates mRNA expression of drug transporters, and this may contribute to the variability of response to atorvastatin.

No description available.

Glutamate, the predominant excitatory neurotransmitter in the central nervous system, is involved in almost all aspects of neurological function including cognition, motor function, memory, learning, decision making, and neuronal plasticity. For normal neurological function, glutamate signaling must be properly regulated. Disrupted glutamate regulation plays a pivotal role in the acute pathophysiology of traumatic brain injury (TBI), disrupting neuronal signaling, initiating secondary injury cascades, and producing excitotoxicity. Increases in extracellular glutamate have been correlated with unfavorable outcomes in TBI survivors, emphasizing the importance of glutamate regulation. The aim of this thesis was to examine disruptions in the regulation of extracellular glutamate after experimental TBI. In these studies, we used glutamate-sensitive microelectrode arrays (MEAs) to examine the regulation of extracellular glutamate two days after diffuse brain injury. First, we examined which brain regions were vulnerable to post-traumatic increases in extracellular glutamate. We detected significant increases in extracellular glutamate in the dentate gyrus and striatum, which correlated to the severity of brain injury. Second, we examined the regulation of extracellular glutamate by neurons and glia to determine the mechanisms responsible for post-traumatic increases in extracellular glutamate. In the striatum of brain-injured rats, we detected significant disruptions in release of glutamate by neurons and significant decreases in the removal of glutamate from the extracellular space by glia. Third, we examined if a novel therapeutic strategy, a viral-vector mediated gene delivery approach, could improve the regulation of extracellular glutamate. Infusion of an adeno-associated virus expressing a glutamate transporter into the rat striatum produced significant improvements in glutamate clearance, identifying a novel strategy to reduce excitotoxicity. Lastly, we examined the translational potential of MEAs as novel neuromonitoring device for clinical TBI research. Overall, these studies have demonstrated the translational potential of MEAs to aid in the diagnosis and treatment of TBI survivors.

In pharmacotherapeutics, the term "correct dosing" is based on the concept that too high a systemic concentration will lead to drug toxicity, while drug levels that are too low may not produce the intended therapeutic effect. Often, the factors determining the ability of a patient to manage a given dose rely on their capacity to efficiently metabolize and eliminate drugs from the body. The liver plays a crucial role in the processing of many clinically relevant drugs via three stages of hepatic drug management. Drugs must first be taken into hepatocytes by uptake transporters. Drugs are then metabolized by phase I and phase II enzymes to make them more manageable. Finally, metabolites are removed from the hepatocyte by efflux transporters either into the bile for elimination or reintroduction to systemic blood. Alterations in one or more of the hepatic drug management stages increase the potential for adverse drug reactions (ADRs).In the United States, ADRs account for between 3%-12% of admissions to hospitals, and approximately 5% of deaths each year. While less than 20% of these cases are due to genetic polymorphisms, the vast majority of ADRs are due to environmental factors including disease. Non-alcoholic fatty liver disease (NAFLD) comprises a spectrum of conditions progressing from steatosis to non-alcoholic steatohepatitis (NASH) and often leading to cirrhosis. Presently, NASH patients represent the greatest population of candidates for liver transplant, illustrating the severity as well as the incidence of this disease. Patients with NAFLD are typically treated for co-existing conditions of the metabolic syndrome (i.e. hyperlipidemina or type II diabetes) and therefore represent a distinct population at risk for adverse drug reactions.The following studies show that experimental NAFLD affects both the signal transduction pathways regulating hepatic drug management genes as well as the hepatic uptake transporter function. Additionally, patient livers diagnosed with progressive stages of NAFLD, display altered CYP activity and efflux transporter expression similar to those previously reported in experimental NAFLD. Given that changes observed in experimental NAFLD result in functional changes in hepatic drug management, similar changes observed in patients with this disease suggest an increased risk for ADRs.

Bacteria have evolved sophisticated cellular transport mechanisms to maintain metal homeostasis to not only utilize metals as important cofactors but also to evade the toxicity of these ions. The delicate balance is maintained by several homeostatic mechanisms that range from active cytoplasmic export, modification, sequestration, and periplasmic detoxification of toxic metals to the extracellular milieu. One mechanism involves active periplasmic extrusion of toxic substrates via a transmembrane spanning tripartite protein complex. The mechanism of substrate binding and subsequent efflux has yet to be elucidated. However, genetic, comparative genomic, biochemical, and functional analyses of the components of the heavy-metal efflux family have allowed the development of proposed models for a substrate transport pathway. The goals of this research were to identify the roles these systems play and to further characterize these systems on a molecular level to ultimately understand the mechanism of substrate transport. Elucidating a transport pathway in metal transporters allows for the development of a revised working model, which ultimately can have implications for antimicrobial drug development.

The body encounters an innumerable amount of foreign substances, termed xenobiotics, which it must remove in order to prevent damage to cells and organs. This system of removal is a collection of processes known as ADME (absorption, distribution, metabolism, and excretion). The dynamics of ADME ultimately determine the fate, or pharmacokinetics, of a xenobiotic in the body whether it be an administered pharmaceutical or a potentially harmful toxicant. The major cellular effectors of ADME are the drug metabolizing enzymes (DMEs) and transporters. DMEs function to transform xenobiotics into a metabolite that is more suitable for excretion, whereas drug transporters serve a two-fold function. They may facilitate the uptake of the xenobiotic into the cell so that it can be acted upon by DMEs, or they may function to actively secrete xenobiotics and metabolites from the cell, encouraging their removal from the body. Any perturbations in the expression or function of these critical cellular effectors can result in the diminished therapeutic effect of a pharmaceutical via accelerated removal from the body, or increased toxicity of a pharmaceutical or toxicant due to retention in the body and increased exposure.Perturbations in the ADME processes may result in adverse drug reactions (ADRs) which are an unintended response to a pharmaceutical when administered at the recommended dose. In the last reporting year, the USFDA documented 471,291 serious ADRs causing hospitalization or permanent disabilities, of which 82,724 resulted in death. ADRs can be categorized as two types: dose-related ADRs, and those that are generally unpredictable and mostly occur in susceptible individuals. The major factors that make a person susceptible to ADRs are genetics and disease; however, genetics account for only a small proportion. This dissertation is focused on the contribution of an environmentally-derived component, particularly liver disease, to the occurrence of ADRs. Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease of industrialized nations. It represents a spectrum of damage progressing to the severe stage of nonalcoholic steatohepatitis (NASH), and is closely related to obesity and type 2 diabetes. The following studies have determined the effect of NAFLD and NASH on DMEs and transporters, and demonstrated the propensity for NASH to result in serious ADRs.