Passive lipoidal diffusion and carrier-mediated cell uptake are both important mechanisms of membrane permeation in drug disposition.

Recently, it has been proposed that drug permeation is essentially carrier-mediated only and that passive lipoidal diffusion is negligible. This opposes the prevailing hypothesis of drug permeation through biological membranes, which integrates the contribution of multiple permeation mechanisms, including both carrier-mediated and passive lipoidal diffusion, depending on the compound's properties, membrane properties, and solution properties. The prevailing hypothesis of drug permeation continues to be successful for application and prediction in drug development. Proponents of the carrier-mediated only concept argue against passive lipoidal diffusion. However, the arguments are not supported by broad pharmaceutics literature. The carrier-mediated only concept lacks substantial supporting evidence and successful applications in drug development.

Pharmacokinetic and pharmacogenetic factors influencing plasma and cellular antiretroviral drug disposition

Abstract: The improvement in antiretroviral drug therapy has transformed HIV infection into a chronic disease. However, treatment failure and drug toxicity are frequent. Inadequate response to treatment is clearly multifactorial and, therefore, dosage individualisation based on demographic factors, genetic markers and measurement of cellular and plasma drug level may enhance both drug efficacy and tolerability. At present, antiretroviral drugs levels are monitored in plasma, whereas only drugs penetrating into cells are able to exert an antiviral activity, suggesting that cellular drug determination may more confidently reflect drug exposure at the site of pharmacological action. The overall objective of this thesis is to provide a better understanding of the Pharmacokinetic and pharmacogenetic factors influencing the plasma and cellular disposition of antiretroviral drugs. To that endeavour, analytical methods for the measurements of plasma and cellular drug levels have been developed and validated using liquid chromatography methods coupled with ultraviolet and tandem mass spectrometry detection, respectively. Correlations between plasma and cellular exposures were assessed during observational and experimental studies. Cytochrome (CYP) 2B6, efflux transporters (ABCB1, ABCC1, ABCC2 and ABCG2) and orosomucoid (ORM) polymorphisms were determined and were related to plasma and cellular exposures, as well as toxicity of antiretroviral drugs. A Pharmacokinetic population model was developed to characterise inter- and intra-patient variability of atazanavir pharmacokinetics, and to identify covariates influencing drug disposition. In that context, a Pharmacokinetic interaction study between atazanavir and lopinavir, both boosted with ritonavir, has beén conducted to assess the safety and pharmacokinetics of this boosted double-protease inhibitors regimen. Well to moderately-correlated cellular and plasma drug levels are .observed or protease inhibitors, whereas for efavirenz and nevirapine these correlations are weak. Cellular exposure, and CYP2B6 genotype (516G>T) are predictors of efavirenz neuropsychological toxicity. Nevirapine plasma exposure is also influenced by CYPZB6 polymorphism. Nelfinavir cellular exposure appears to be significantly associated only with ABCB1 genotype (3435C>T and intron 26 + 80T>C). Indinavir and lopinavir clearance and lopinavir cellular/plasma exposure ratio are influenced by the concentration of the variant S of ORM, suggesting-a specific binding of these drugs to this variant. Nelfinavir and efavirenz are not influenced by ORM concentration and phenotype. The Pharmacokinetic parameters of atazanavir are adequately described by our population model. The atazanavir-lopinavir interaction study indicates no influence on plasma and cellular atazanavir pharmacokinetics, while limited decrease in lopinavir concentrations was observed after atazanavir addition. The residual variability unexplained by the considered variables suggests that other covariates either uncontrolled at present or remaining to be identified, such as genetic and environmental factors influence antiretroviral drug pharmacokinetics, with substantial impact on treatment efficacy and tolerability. In that context, a comprehensive approach taking into account drug pharmacokinetics and patient genetic background is expected to contribute to increase treatment success, and to reduce the occurrence of adverse drug reactions by stratifying patients in an individualised antiretroviral therapy approach. Résumé Facteurs pharmacocinétiques et pharmacogénétiques influençant l'exposition plasmatique et cellulaire des antirétroviraux Les progrès de la thérapie antirétrovirale ont transformé l'infection par le VIH d'une affection mortelle à une maladie chronique. En dépit de ce succès, l'échec thérapeutique et la toxicité médicamenteuse restent fréquents. Une réponse inadéquate au traitement est clairement multifactorielle et une individualisation de la posologie des médicaments qui se baserait sur les facteurs démographiques et génétiques des patients et sur les taux sanguins des médicaments pourrait améliorer à la fois l'efficacité et la tolérance de la thérapie. Par ailleurs, seules les concentrations plasmatiques sont actuellement considérées pour le suivi thérapeutique des médicaments, alors que les taux cellulaires pourraient mieux refléter l'activité de ses médicaments qui agissent au niveau intracellulaire. L'objectif global de cette thèse était de mieux comprendre les facteurs pharmacocinétiques et pharmacocénétiques influençant l'exposition plasmatique et cellulaire des médicaments antirétroviraux. A cet effet, des méthodes pour quantifier les concentrations plasmatiques et cellulaires des antirétroviraux ont été développées et validées en utilisant la chromatographie liquide couplée à la détection ultraviolette et la spectrométrie de masse en tandem, respectivement. La corrélation entre l'exposition cellulaire et plasmatique de ces médicaments a été étudiée lors d'études observationnelles et expérimentales. Les polymorphismes du cytochrome (CYP) 2B6, ainsi que des transporteurs d'efflux (ABCB1, ABCC1, ABCC2 et ABCG2) et de l'orosomucoïde (ORM) ont été déterminés et corrélés avec l'exposition plasmatique et cellulaire des antirétroviraux, ainsi qu'à leur toxicité. Un modèle de pharmacocinétique de population a été établi afin de caractériser la variabilité inter- et intra-individuelle de l'atazanavir, et d'identifier les covariables pouvant influencer le devenir de ce médicament. Dans ce contexte, une étude d'interaction entre l'atazanavir et le lopinavir a été effectuée afin de déterminer la sécurité et le profil pharmacocinétique de ce régime thérapeutique. Des corrélations modérées à bonnes ont été observées entre les taux cellulaires et plasmatiques des inhibiteurs de protéase, alors que pour l'efavirenz et la névirapine ces corrélations sont faibles. L'exposition cellulaire, ainsi que le génotype du CYP2B6 (516G>T) sont des indices de la toxicité neuropsychologique de l'efavirenz. L'exposition plasmatique de la névirapine est également influencée par le polymorphisme du CYPZB6. L'exposition cellulaire du nelfinavir est significativement associée au génotype du ABCB1 (3435C>T et intron 26 + 80T>C). La clairance de l'indinavir et du lopinavir, ainsi que le rapport entre exposition cellulaire et plasmatique du lopinavir sont influencés par la concentration du variant S de l'ORM, suggérant une liaison spécifique de ces médicaments à ce variant. La clairance du nelfinavir et de l'efavirenz n'est pas influencée ni par la concentration ni par le phénotype de l'ORM. Les paramètres pharmacocinétiques de l'atazanavir ont été décrits de façon adéquate par le modèle de population proposé. De plus, le lopinavir n'influence pas les concentrations plasmatiques et cellulaires de l'atazanavir; alors que celui-ci conduit à une baisse limitée des taux de lopinavir. L'importante variabilité pharmacocinétique des antirétroviraux suggère que d'autres facteurs génétiques et environnementaux -qui restent encore à découvrir- influencent également leur disponibilité. Dans un proche futur, une prise en charge qui tienne. compte de la pharmacocinétique des médicaments et des caractéristiques génétiques du patient devrait permettre d'individualiser le traitement, contribuant certainement à une amélioration de la réponse thérapeutique et à une diminution de la toxicité. Résumé grand public Facteurs pharmacocinétiques et pharmacogénétiques influençant l'exposition plasmatique et cellulaire des antirétroviraux Les progrès effectués dans le traitement de l'infection par le virus de l'immunodéficience humaine acquise (VIH), ont permis de transformer une maladie avec un pronostic sombre, en une maladie chronique traitable avec des médicaments de plus en plus efficaces. Malgré ce succès, de nombreux patients ne répondent pas de façon optimale à leur traitement et/ou souffrent d'effets indésirables médicamenteux entraînant fréquemment une modification de leur thérapie. Actuellement, le suivi de la réponse au traitement s'effectue par la mesure chez les patients de la quantité de virus et du nombre des cellules immunitaires dans le sang, ainsi que par la concentration sanguine des médicaments administrés. Cependant, comme le virus se réplique à l'intérieur de la cellule, la mesure des concentrations médicamenteuses au niveau intracellulaire pourrait mieux refléter l'activité pharmacologique au site d'action. De plus, il a été possible de mettre en évidence la grande variabilité des concentrations plasmatiques de médicaments chez des patients prenant pourtant la même dose de médicament. Comme cette variabilité est notamment due à des facteurs génétiques qui sont susceptibles d'influencer la réponse au traitement antirétroviral, des analyses génétiques ont été également effectuées chez ces patients. Cette thèse a eu pour objectif de mieux comprendre les facteurs pharmacologiques et génétiques influençant l'activité et la toxicité des médicaments antirétroviraux afin de réduire la variabilité de la réponse thérapeutique. A cet effet, une méthode de dosage permettant la quantification des médicaments anti-HIV au niveau intracellulaire a été développée. Par ailleurs, nos études ont également porté .sur les variations génétiques influençant la quantité et l'activité des protéines impliquées dans le métabolisme et dans le transport des médicaments antirétroviraux. Enfin, les conséquences de ces variations sur la réponse clinique et la toxicité du traitement ont été évaluées. Nos études ont mis en évidence des associations significatives entre les variations génétiques considérées et la concentration sanguine, cellulaire et la toxicité de quelques médicaments antirétroviraux. La complémentarité des connaissances pharmacologiques, génétiques et virales pourrait aboutir à une stratégie globale permettant d'individualiser le traitement et la dose administrée, en fonction des caractéristiques propres de chaque patient. Cette approche pourrait contribuer à une optimisation du traitement antirétroviral dans la perspective d'une meilleure- efficacité thérapeutique à long terme et d'une diminution des effets indésirables rencontrés.

Impact of cholesterol on ABC and SLC transporters expression and function and its role in disposition variability to lipid-lowering drugs

This report focuses on the effects of cholesterol on the expression and function of the ATP-binding cassette (ABCB1, ABCG2 and ABCC2) and solute-linked carrier (SLCO1B1 and SLCO2B1) drug transporters with a particular focus on the potential impact of cholesterol on lipid-lowering drug disposition. Statins are the most active agents in the treatment of hypercholesterolemia. However, considerable interindividual variation exists in the response to statin therapy. Therefore, it would be huge progress if factors were identified that reliably differentiate between responders and nonresponders. Many studies have suggested that plasma lipid concentrations can affect drug disposition of compounds, such as ciclosporin and amphotericin B. Both compounds are able to affect the expression and function of ABC transporters. Although still speculative, these effects might be owing to the regulation of drug transporters by plasma cholesterol levels. Studies with normo- and hyper-cholesterolemic individuals, before and after atorvastatin treatment, have demonstrated that plasma cholesterol levels are correlated with drug transporter expression, as well as being related to atorvastatin`s cholesterol-lowering effect. The mechanism influencing the correlation between cholesterol levels and the expression and function of drug transporters remains unclear. Some studies provide strong evidence that nuclear receptors, such as the pregnane X receptor and the constitutive androstane receptor, mediate this effect. In the near future, pharmacogenomic studies with individuals in a pathological state should be performed in order to identify whether high plasma cholesterol levels might be a factor contributing to interindividual oral drug bioavailability.

Cationic drug pharmacokinetics in diseased livers determined by fibrosis index, hepatic protein content, microsomal activity, and nature of drug

The disposition kinetics of six cationic drugs in perfused diseased and normal rat livers were determined by multiple indicator dilution and related to the drug physicochemical properties and liver histopathology. A carbon tetrachloride (CCl4)induced acute hepatocellular injury model had a higher fibrosis index (FI), determined by computer-assisted image analysis, than did an alcohol-induced chronic hepatocellular injury model. The alcohol-treated group had the highest hepatic alpha(1)- acid glycoprotein, microsomal protein (MP), and cytochrome P450 (P450) concentrations. Various pharmacokinetic parameters could be related to the octanol-water partition coefficient (log P-app) of the drug as a surrogate for plasma membrane partition coefficient and affinity for MP or P450, the dependence being lower in the CCl4-treated group and higher in the alcohol-treated group relative to controls. Stepwise regression analysis showed that hepatic extraction ratio, permeability-surface area product, tissue-binding constant, intrinsic clearance, partition ratio of influx (k(in)) and efflux rate constant (k(out)), and k(in)/k(out) were related to physicochemical properties of drug (log P-app or pK(a)) and liver histopathology (FI, MP, or P450). In addition, hepatocyte organelle ion trapping of cationic drugs was evident in all groups. It is concluded that fibrosis-inducing hepatic disease effects on cationic drug disposition in the liver may be predicted from drug properties and liver histopathology.

Importance of influx and efflux systems and xenobiotic metabolizing enzymes in intratumoral disposition of anticancer agents.

In this review, intratumoral drug disposition will be integrated into the wide range of resistance mechanisms to anticancer agents with particular emphasis on targeted protein kinase inhibitors. Six rules will be established: 1. There is a high variability of extracellular/intracellular drug level ratios; 2. There are three main systems involved in intratumoral drug disposition that are composed of SLC, ABC and XME enzymes; 3. There is a synergistic interplay between these three systems; 4. In cancer subclones, there is a strong genomic instability that leads to a highly variable expression of SLC, ABC or XME enzymes; 5. Tumor-expressed metabolizing enzymes play a role in tumor-specific ADME and cell survival and 6. These three systems are involved in the appearance of resistance (transient event) or in the resistance itself. In addition, this article will investigate whether the overexpression of some ABC and XME systems in cancer cells is just a random consequence of DNA/chromosomal instability, hypo- or hypermethylation and microRNA deregulation, or a more organized modification induced by transposable elements. Experiments will also have to establish if these tumor-expressed enzymes participate in cell metabolism or in tumor-specific ADME or if they are only markers of clonal evolution and genomic deregulation. Eventually, the review will underline that the fate of anticancer agents in cancer cells should be more thoroughly investigated from drug discovery to clinical studies. Indeed, inhibition of tumor expressed metabolizing enzymes could strongly increase drug disposition, specifically in the target cells resulting in more efficient therapies.

Implementation of bayesian therapeutic drug monitoring in modern patient care

The variability observed in drug exposure has a direct impact on the overall response to drug. The largest part of variability between dose and drug response resides in the pharmacokinetic phase, i.e. in the dose-concentration relationship. Among possibilities offered to clinicians, Therapeutic Drug Monitoring (TDM; Monitoring of drug concentration measurements) is one of the useful tool to guide pharmacotherapy. TDM aims at optimizing treatments by individualizing dosage regimens based on blood drug concentration measurement. Bayesian calculations, relying on population pharmacokinetic approach, currently represent the gold standard TDM strategy. However, it requires expertise and computational assistance, thus limiting its large implementation in routine patient care. The overall objective of this thesis was to implement robust tools to provide Bayesian TDM to clinician in modern routine patient care. To that endeavour, aims were (i) to elaborate an efficient and ergonomic computer tool for Bayesian TDM: EzeCHieL (ii) to provide algorithms for drug concentration Bayesian forecasting and software validation, relying on population pharmacokinetics (iii) to address some relevant issues encountered in clinical practice with a focus on neonates and drug adherence. First, the current stage of the existing software was reviewed and allows establishing specifications for the development of EzeCHieL. Then, in close collaboration with software engineers a fully integrated software, EzeCHieL, has been elaborated. EzeCHieL provides population-based predictions and Bayesian forecasting and an easy-to-use interface. It enables to assess the expectedness of an observed concentration in a patient compared to the whole population (via percentiles), to assess the suitability of the predicted concentration relative to the targeted concentration and to provide dosing adjustment. It allows thus a priori and a posteriori Bayesian drug dosing individualization. Implementation of Bayesian methods requires drug disposition characterisation and variability quantification trough population approach. Population pharmacokinetic analyses have been performed and Bayesian estimators have been provided for candidate drugs in population of interest: anti-infectious drugs administered to neonates (gentamicin and imipenem). Developed models were implemented in EzeCHieL and also served as validation tool in comparing EzeCHieL concentration predictions against predictions from the reference software (NONMEM®). Models used need to be adequate and reliable. For instance, extrapolation is not possible from adults or children to neonates. Therefore, this work proposes models for neonates based on the developmental pharmacokinetics concept. Patients' adherence is also an important concern for drug models development and for a successful outcome of the pharmacotherapy. A last study attempts to assess impact of routine patient adherence measurement on models definition and TDM interpretation. In conclusion, our results offer solutions to assist clinicians in interpreting blood drug concentrations and to improve the appropriateness of drug dosing in routine clinical practice.

Renal Drug Transporters – Clinical Significance and Role in Drug-Drug Interactions

Thesis (Ph.D.)--University of Washington, 2016-07

Statin regulation of CYP3A4 and CYP3A5 expression

CYP3A4 and CYP3A5 are cytochrome P450 enzymes that are highly expressed in the liver and gut and metabolize endogenous compounds and xenobiotics. Statins are cholesterol-lowering drugs that are extensively metabolized by CYP3A4 and CYP3A5. The bioavailability of statins is affected by CYP3A4 and CYP3A5 and glucuronidases metabolism as well as uptake and efflux transporters that affect drug disposition. CYP3A4 and CYP3A5 variants have been demonstrated to influence the pharmacokinetics, efficacy and safety of statins. Inducers and inhibitors of CYP3A4 and CYP3A5 play an important role in reducing statin efficacy and increase the risk of adverse effects, respectively. Statins have been demonstrated to increase CYP3A expression in vitro, most likely because they are ligands to nuclear receptors (pregnane X receptor and constitutive androsterone receptor) that form heterodimers with retinoid X receptors and bind to responsive elements in the CYP3A4 and CYP3A5 promoter regions. This special report outlines the earlier studies on variability of response to statins owing to CYP3A variants and highlights findings on the induction of CYP3A4 and CYP3A5 expression by statins.

Stereoselective analysis of carvedilol in human plasma and urine using HPLC after chiral derivatization

An enantioselective high-performance liquid chromatographic method for the analysis of carvedilol in plasma and urine was developed and validated using (-)-menthyl chloroformate (MCF) as a derivatizing reagent. Chloroform was used for extraction, and analysis was performed by HPLC on a C18 column with a fluorescence detector. The quantitation limit was 0.25 ng/ml for S(-)-carvedilol in plasma and 0.5 ng/ml for R(+)-carvedilol in plasma and for both enantiomers in urine. The method was applied to the study of enantioselectivity in the pharmacokinetics of carvedilol administered in a multiple dose regimen (25mg/12h) to a hypertensive elderly female patient. The data obtained demonstrated highest plasma levels for the R(+)-carvedilol(AUCSS 75.64 vs 37.29ng/ml). The enantiomeric ratio R(+)/S(-) was 2.03 for plasma and 1.49 0 - 12 for urine (Aeo-12 17.4 vs 11.7 pg). Copyright (c) 2008 John Wiley & Sons, Ltd.

The pharmacokinetics of once-daily dosing of ceftriaxone in critically ill patients

The aim of this study was to determine the pharmacokinetic profile of the normal recommended dose of ceftriaxone in critically ill patients and to establish whether the current daily dosing recommendation maintains plasma concentrations adequate for antibacterial efficacy. Ceftriaxone at a recommended dose of 2 g iv was administered od to 12 critically ill patients with severe sepsis and normal serum creatinine concentrations. Blood samples were taken at predetermined intervals over the first 24 h and on day 3 for measurement of ceftriaxone concentrations. There was wide variability in drug disposition, explained by the presence of variable renal function and identified by the measurement of creatinine clearance. In nine patients with normal renal function, there was a high level of creatinine clearance(mean +/- S.D., 41 +/- 12 mL/min) and volume of distribution (20 +/- 3.3 L), which resulted in an elimination half-life of 6.4 +/- 1.1 h. In comparison with normal subjects, ceftriaxone clearance was increased 100%, volume of distribution increased 90% and the elimination half-life was similar. Three patients had substantially suboptimal plasma ceftriaxone concentrations. We confirm previous findings that ceftriaxone clearance in critically ill patients correlates with renal clearance by glomerular filtration. The elimination half-life is prolonged (21.4 +/- 9.8 h) in critically ill patients with renal failure when compared with previously published data in non-critically ill patients with renal failure. We conclude that in critically ill patients with normal renal function, inadequate plasma concentrations may result following od bolus dosing of ceftriaxone. Drug accumulation may occur in critically ill patients with renal failure.

Causes développementales dans la variabilité de l'efficacité et de la toxicité des antalgiques en pédiatrie [Developmental causes in variability of efficacy and toxicity of analgesics in pediatrics]

The intensity of pain perception and its sensibility to analgesic drugs is highly variable and unpredictable between individuals. Drug disposition varies during development due to the physiological maturation of enzymatic systems and physiological processes responsible for the absorption, distribution, elimination and effect at the site of action. Many of those developmental variables are not yet clearly defined, but their consideration is important for avoiding potential risks of ineffective or toxic treatment. Implications of those developmental changes for day-to-day clinical practice depend on the age of the child, on the type of drug, on the underlying disease and on the potential co-administration of other chemicals.

In vitro biotransformation of imatinib by the tumor expressed CYP1A1 and CYP1B1.

The main objective of the study was to examine the biotransformation of the anticancer drug imatinib in target cells by incubating it with oxidoreductases expressed in tumor cells. The second objective was to obtain an in silico prediction of the potential activity of imatinib metabolites. An in vitro enzyme kinetic study was performed with cDNA expressed human oxidoreductases and LC-MS/MS analysis. The kinetic parameters (Km and Vmax) were determined for six metabolites. A molecular modeling approach was used to dock these metabolites to the target Abl or Bcr-Abl kinases. CYP3A4 isozyme showed the broadest metabolic capacity, whereas CYP1A1, CYP1B1 and FMO3 isozymes biotransformed imatinib with a high intrinsic clearance. The predicted binding modes for the metabolites to Abl were comparable to that of the parent drug, suggesting potential activity. These findings indicate that CYP1A1 and CYP1B1, which are known to be overexpressed in a wide range of tumors, are involved in the biotransformation of imatinib. They could play a role in imatinib disposition in the targeted stem, progenitor and differentiated cancer cells, with a possible contribution of the metabolites toward the activity of the drug.

Pharmacogenomics of HIV Therapy: Summary of a Workshop Sponsored by the National Institute of Allergy and Infectious Diseases

Approximately 1 million people in the United States and over 30 million worldwide are living with human immunodeficiency virus type 1 (HIV-1). While mortality from untreated infection approaches 100%, survival improves markedly with use of contemporary antiretroviral therapies (ART). In the United States, 25 drugs are approved for treating HIV-1, and increasing numbers are available in resource-limited countries. Safe and effective ART is a cornerstone in the global struggle against the acquired immunodeficiency syndrome. Variable responses to ART are due at least in part to human genetic variants that affect drug metabolism, drug disposition, and off-site drug targets. Defining effects of human genetic variants on HIV treatment toxicity, efficacy, and pharmacokinetics has far-reaching implications. In 2010, the National Institute of Allergy and Infectious Diseases sponsored a workshop entitled, Pharmacogenomics A Path Towards Personalized HIV Care. This article summarizes workshop objectives, presentations, discussions, and recommendations derived from this meeting.

Pharmacogenetics of Antiviral Treatment

RESUME - FRANÇAISRésuméDans ce travail de thèse, l'importance de la pharmacogénétique des traitements antiviraux a été évaluée en déterminant, au moyen de trois différentes approches, l'impact de variations génétiques sur la pharmacocinétique de deux traitements antirétroviraux (à savoir l'efavirenz et le lopinavir) ainsi que sur la capacité de pouvoir éliminer le virus de l'hépatite C de façon naturelle ou suite à un traitement médicamenteux.L'influence des variations génétiques sur les taux plasmatiques de l'efavirenz et de ses métabolites primaires a été évaluée par l'analyse d'un seul gène candidat : le cytochrome P450 (CYP) 2A6, impliqué dans une voie métabolique accessoire de l'efavirenz. Cette étude a permis de démontrer que le génotype du CYP2A6 devient cliniquement déterminant en l'absence de fonction du CYP2B6, impliqué dans la voie métabolique principale, et que la perte simultanée des voies métaboliques principales et accessoires entraine une augmen¬tation du risque d'interruption du traitement, soulignant la valeur prédictive du génotypage.L'influence de la génétique sur la clairance du lopinavir a été évaluée par l'analyse à grande échelle de gènes candidats, à savoir les gènes potentiellement impliqués dans l'absorption, le métabolisme, la distribution et l'élimination d'un médicament. Cette étude a permis l'identification de 4 polymorphismes, dans des transporteurs et des enzymes métaboliques, associés à la clairance du lopinavir et expliquant 5% de la variabilité inter¬individuelle de ce phénotype.L'influence de la génétique sur la capacité d'éliminer le virus de l'hépatite C, de façon naturelle ou à la suite d'un traitement, a été évaluée par l'analyse du génome entier. Cette étude a permis l'identification d'un polymorphisme situé à proximité de l'interféron-X3. Quatre variations génétiques potentiellement causales ont ensuite pu être identifiées par reséquencage. Finalement, la contribution nette de ce gène sur l'élimination du virus a pu être évaluée dans une cohorte infectée par une seule et même source, permettant ainsi de contrôler l'effet de la diversité virale, du genre et de la présence de co-infections.Cette thèse a permis de mettre en évidence les diverses méthodes disponibles pour la recherche en pharmacogénétique, ainsi que l'importance du reséquencage pour l'identification de variations génétiques causales.SUMMARY - ENGLISHSummaryIn this thesis work the relevance of pharmacogenetics of antiviral treatment has been assessed by investigating, through three different approaches, the impact of host genetic variation on antiretroviral drug disposition (namely efavirenz and lopinavir) and on natural or treatment-induced clearance of hepatitis C virus.The influence of host genetic variation on efavirenz and its primary metabolite plasma levels was assessed by single candidate gene approach, through comprehensive analysis of cytochrome P450 (CYP) 2A6 - involved in efavirenz accessory metabolic pathway. The study could demonstrate that CYP2A6 genotype became increasingly relevant in the setting of limited CYP2B6 function - involved in efavirenz main metabolic pathway - and that individuals with both main and accessory metabolic pathways impaired were at higher risk for treatment discontinuation, overall emphasizing the predictive power of genotyping.The influence of host genetic variation on lopinavir clearance was assessed by large scale candidate gene approach, through analysis of genes involved in the absorption, distribution, metabolism and elimination. The study identified four genetic variants in drug transporters and metabolizing enzymes that explained 5% of the interindividual variability in lopinavir clearance.The influence of host genetic variation on hepatitis C virus (HCV) natural or treatment- induced clearance was assessed through genome-wide association study approach. This study identified an intergenic polymorphism, part of a linkage disequilibrium block encompassing the interferon-3 gene, as highly associated with treatment-induced and spontaneous HCV clearance. Resequencing and recombinant mapping lead to the identification of four potentially causal genetic variants. Finally, we could assess the net contribution of genetic variants in interferon-3 to clearance by controlling for viral diversity, gender and co-infection status in a single source infected cohort.This thesis highlights the various genetic tools available to pharmacogenetic discovery (candidate gene, pathway or and genome-wide approaches), and the importance of resequencing for mapping of causal variants.

High baseline serum total and LDL cholesterol levels are associated with MDR1 haplotypes in Brazilian hypercholesterolemic individuals of European descent

The MDR1 gene encodes the P-glycoprotein, an efflux transporter with broad substrate specificity. P-glycoprotein has raised great interest in pharmacogenetics because it transports a variety of structurally divergent drugs, including lipid-lowering drugs. The synonymous single-nucleotide polymorphism C3435T and the nonsynonymous single-nucleotide polymorphism G2677T/A in MDR1 have been indicated as potential determinants of variability in drug disposition and efficacy. In order to evaluate the effect of G2677T/A and C3435T MDR1 polymorphisms on serum levels of lipids before and after atorvastatin administration, 69 unrelated hypercholesterolemic individuals from São Paulo city, Brazil, were selected and treated with 10 mg atorvastatin orally once daily for four weeks. MDR1 polymorphisms were analyzed by PCR-RFLP. C3435T and G2677T polymorphisms were found to be linked. The allelic frequencies for C3435T polymorphism were 0.536 and 0.464 for the 3435C and 3435T alleles, respectively, while for G2677T/A polymorphism allele frequencies were 0.580 for the 2677G allele, 0.384 for the 2677T allele and 0.036 for the 2677A allele. There was no significant relation between atorvastatin response and MDR1 polymorphisms (repeated measures ANOVA; P > 0.05). However, haplotype analysis revealed an association between T/T carriers and higher basal serum total (TC) and LDL cholesterol levels (TC: 303 ± 56, LDL-C: 216 ± 57 mg/dl, respectively) compared with non-T/T carriers (TC: 278 ± 28, LDL-C: 189 ± 24 mg/dl; repeated measures ANOVA/Tukey test; P < 0.05). These data indicate that MDR1 polymorphism may have an important contribution to the control of basal serum cholesterol levels in Brazilian hypercholesterolemic individuals of European descent.