Torsemide renal clearance and genetic variation in luminal and basolateral organic anion transporters

Detection of potential drug-drug interactions for risk of acute kidney injury: a population-based case-control study using interpretable machine-learning models

Background: Acute kidney injury (AKI), with an increase in serum creatinine, is a common adverse drug event. Although various clinical studies have investigated whether a combination of two nephrotoxic drugs has an increased risk of AKI using traditional statistical models such as multivariable logistic regression (MLR), the evaluation metrics have not been evaluated despite the fact that traditional statistical models may over-fit the data. The aim of the present study was to detect drug-drug interactions with an increased risk of AKI by interpreting machine-learning models to avoid overfitting. Methods: We developed six machine-learning models trained using electronic medical records: MLR, logistic least absolute shrinkage and selection operator regression (LLR), random forest, extreme gradient boosting (XGB) tree, and two support vector machine models (kernel = linear function and radial basis function). In order to detect drug-drug interactions, the XGB and LLR models that showed good predictive performance were interpreted by SHapley Additive exPlanations (SHAP) and relative excess risk due to interaction (RERI), respectively. Results: Among approximately 2.5 million patients, 65,667 patients were extracted from the electronic medical records, and assigned to case (N = 5,319) and control (N = 60,348) groups. In the XGB model, a combination of loop diuretic and histamine H₂ blocker [mean (|SHAP|) = 0.011] was identified as a relatively important risk factor for AKI. The combination of loop diuretic and H₂ blocker showed a significant synergistic interaction on an additive scale (RERI 1.289, 95% confidence interval 0.226-5.591) also in the LLR model. Conclusion: The present population-based case-control study using interpretable machine-learning models suggested that although the relative importance of the individual and combined effects of loop diuretics and H₂ blockers is lower than that of well-known risk factors such as older age and sex, concomitant use of a loop diuretic and histamine H₂ blocker is associated with increased risk of AKI.

Risk Factors of Renal Tubular Dysfunction in Thai People Living with HIV Receiving Tenofovir Disoproxil Fumarate

Tenofovir disoproxil fumarate (TDF) associates with renal tubular dysfunction (RTD) in some people living with HIV (PLWH). We studied clinical and genetic factors associated with RTD in Thai PLWH receiving TDF. RTD was diagnosed in 13 of 65 (20%) patients. The median (interquartile range) age and CD4 cell counts were 43.8 (40.4-50.9) years and 554 (437-716) cells/mm³, respectively. The median duration of TDF use was 46.9 (31.5-54.1) months. Univariate logistic regression demonstrated body mass index (BMI), concomitant use of protease inhibitor (PI), hyperlipidemia, and homozygous C/C SNP rs1059751 of ABCC4 gene as predisposing factors of RTD. In multivariate model, concomitant use of PI [adjusted odds ratio (aOR) 11.39; 95% confidence interval (CI), 1.59- 81.56; P = 0.015], hyperlipidemia (aOR 8.59; 95% CI, 1.46-50.40; P = 0.017), and BMI (aOR 0.76; 95% CI, 0.59-0.98; P = 0.037) remained associated with RTD in patients receiving TDF. PLWH receiving TDF with the presence of these factors should be closely monitored for RTD.

Population Pharmacokinetic (Pop-PK) Analysis of Torsemide in Healthy Korean Males Considering CYP2C9 and OATP1B1 Genetic Polymorphisms

Torsemide is a diuretic drug used for several cardiovascular and chronic diseases. With regard to the clinical application of torsemide, studies on individualized pharmacotherapy and modeling that take variability in pharmacokinetics (PKs) within a population into account have been rarely reported. Thus, the objective of this study was to perform population pharmacokinetic (Pop-PK) modeling and to identify effective covariates that could explain the inter-individual variability (IIV) of torsemide PK. Pop-PK modeling for torsemide was performed based on serum concentration data obtained from 112 healthy Korean males and analysis of various genetic and physicochemical parameters. Modeling was performed with nonlinear mixed-effects (NLME) using Phoenix NLME. The finally developed model was fully verified. The model was also reconfirmed using NONMEM software. As a basic model, the PKs of torsemide within the population were well described by a two-compartment model reflecting the lag-time on oral absorption. According to the genetic polymorphisms of OATP1B1 and CYP2C9, significant associations were found in the V/F, CL/F, and CL₂/F of torsemide. These were reflected as effective covariates in the final Pop-PK model of torsemide, resulting in an approximately 5–10% improvement in the model parameter IIV values. Considering that torsemide is a substrate for CYP2C9 and OATP1B1, it was important to search for genetic polymorphisms in CYP2C9 and OATP1B1 as covariates to explain the PK diversity of torsemide between individuals. The differences in CL/F and CL₂/F between the phenotypes of CYP2C9 were approximately 36.5–51%. The difference in V/F between the phenotypes of OATP1B1 was approximately 41–64.6%. These results suggested that the phenotypes of CYP2C9 and OATP1B1 produced significant differences in torsemide PKs. Considering that CYP2C9 and OATP1B1 phenotypes as covariates affected different PK parameters of torsemide, it could be inferred that torsemide’s cell membrane permeation process by OATP1B1 and the metabolic process by CYP2C9 could independently affect each other in vivo without interplay. There was no significant difference in the parameter estimates between modeling software (Phoenix NLME vs. NONMEM). In this study, the torsemide PK variability between individuals was largely explained. In the future, individualized effective drug therapy of torsemide taking individual patient’s genotypes into account might become possible.

Sex-related differences in the pharmacological treatment of heart failure

Heart failure (HF) represents a leading cause of morbidity and mortality. However, HF trials highlighted many differences between men and women with HF. Thus, women represent approximately a quarter of people with HF with reduced ejection fraction (HFrEF), while they account for over half of those with HF with preserved EF (HFpEF). There are also sex-related differences (SRDs) in the pharmacokinetics, pharmacodynamics and safety profile of some guideline-recommended drugs for the treatment of HF. As compared with men, women with HFrEF are less often treated with guideline-recommended HF drugs, experience more frequent and severe adverse reactions when these drugs are prescribed at the same doses in both sexes, and recent evidence suggests that women might need lower doses than men, bringing into question which are the optimal doses of HF drugs in women and men separately. However, information on SRDs in drug efficacy and safety in patients with HFrEF is very limited due to the underrepresentation of women and the lack of sex-specific evaluations of drug efficacy and safety in HF clinical trials. As a consequence, current clinical guidelines do not provide sex-specific recommendations, even when significant differences exist, at least, in drug safety. The aim of this article is to review the SRDs in the pharmacokinetics, efficacy and safety of guideline-recommended HF drugs and to identify emerging areas of research to improve our understanding of the SRDs, because a better understanding of these differences is the first step to achieve a personalized treatment of HF in women and men.

Pharmacogenetics-Based Preliminary Algorithm to Predict the Incidence of Infection in Patients Receiving Cytotoxic Chemotherapy for Hematological Malignancies: A Discovery Cohort

Introduction: Infections in hematological cancer patients are common and usually life-threatening; avoiding them could decrease morbidity, mortality, and cost. Genes associated with antineoplastics’ pharmacokinetics or with the immune/inflammatory response could explain variability in infection occurrence.

Objective: To build a pharmacogenetic-based algorithm to predict the incidence of infections in patients undergoing cytotoxic chemotherapy.

Methods: Prospective cohort study in adult patients receiving cytotoxic chemotherapy to treat leukemia, lymphoma, or myeloma in two hospitals in Santiago, Chile. We constructed the predictive model using logistic regression. We assessed thirteen genetic polymorphisms (including nine pharmacokinetic—related genes and four inflammatory response-related genes) and sociodemographic/clinical variables to be incorporated into the model. The model’s calibration and discrimination were used to compare models; they were assessed by the Hosmer-Lemeshow goodness-of-fit test and area under the ROC curve, respectively, in association with Pseudo-R².

Results: We analyzed 203 chemotherapy cycles in 50 patients (47.8 ± 16.1 years; 56% women), including 13 (26%) with acute lymphoblastic and 12 (24%) with myeloblastic leukemia.

Pharmacokinetics-related polymorphisms incorporated into the model were CYP3A4 rs2242480C>T and OAT4 rs11231809T>A. Immune/inflammatory response-related polymorphisms were TLR2 rs4696480T>A and IL-6 rs1800796C>G. Clinical/demographic variables incorporated into the model were chemotherapy type and cycle, diagnosis, days in neutropenia, age, and sex. The Pseudo-R² was 0.56, the p-value of the Hosmer-Lemeshow test was 0.98, showing good goodness-of-fit, and the area under the ROC curve was 0.93, showing good diagnostic accuracy.

Conclusions: Genetics can help to predict infections in patients undergoing chemotherapy. This algorithm should be validated and could be used to save lives, decrease economic costs, and optimize limited health resources.

Pharmacogenetics as a Way for Personalizing Diuretic Therapy: Focus on Torasemide

Optimizing diuretic therapy in patients with chronic heart failure is a complicated problem with many unresolved questions. Diuretics take an important place in the treatment of heart failure, which are used in almost 80% of cases. Currently, there are not enough clinical studies, which comparative effectiveness of loop diuretics, as well as studies aimed at personalizing diuretic therapy. Torasemide has several advantages over other loop diuretics; high bioavailability, longer half-life and duration of action provide predictable diuresis. The presence of favorable neurohormonal effects, consisting in a decrease of sympathetic activity and inhibition of the renin-angiotensin-aldosterone system, leads to the fact that hypokalemia rarely occurs. In addition, torasemide slows development of myocardial fibrosis and fosters reverse ventricular remodelling. The use of personalization methods is one of the ways to increase the efficiency and safety of pharmacotherapy with diuretics. The polymorphism of genes encoding systems of biotransformation and transporters of drug is an important factor that determines the individual characteristics of a patient. Pharmacogenetics of torasemide may be of significant importance for pharmacokinetics and pharmacodynamics, influencing the intensity of the diuretic effect and side effects. The clearance of torasemide after oral administration may vary by 47% due to genetic characteristics: the participation of the OATP1B1 polymorphism is approximately 15.5%, the CYP2C9 polymorphism is 20%, and the OAT1 and OAT4 polymorphisms are 10%. Due to the significant differences in the pharmacokinetics of torasemide, further study of the pharmacodynamic characteristics of torasemide in patients with genetic polymorphism is necessary.

The effects of drug transporters on the efficacy of methotrexate in the treatment of rheumatoid arthritis

The ATP-binding cassette (ABC) and solute carrier (SLC) transporter families consist of common drug transporters that mediate the efflux and uptake of drugs, respectively, and play an important role in the absorption, distribution, metabolism and excretion of drugs in vivo. Rheumatoid arthritis (RA) is an autoimmune disease characterized by erosive arthritis, and there are many RA patients worldwide. Methotrexate (MTX), the first-choice treatment for RA, can reduce the level of inflammation, prevent joint erosion and functional damage, and greatly reduce pain in RA patients. However, many patients show resistance to MTX, greatly affecting the efficacy of MTX. Many factors, such as irrational drug use and heredity, are associated with drug resistance. Considering the effect of drug transporters on drugs, many studies have compared the expression of drug transporters in drug-resistant and drug-sensitive patients, and abnormal transporter expression and transport activity have been found in patients with MTX resistance. Thus, drug transporters are involved in drug resistance. This article reviews the effects of transporters on the efficacy of MTX in the treatment of RA.

Physiologically Based Pharmacokinetic Models of Probenecid and Furosemide to Predict Transporter Mediated Drug-Drug Interactions

Purpose

To provide whole-body physiologically based pharmacokinetic (PBPK) models of the potent clinical organic anion transporter (OAT) inhibitor probenecid and the clinical OAT victim drug furosemide for their application in transporter-based drug-drug interaction (DDI) modeling.

Methods

PBPK models of probenecid and furosemide were developed in PK-Sim®. Drug-dependent parameters and plasma concentration-time profiles following intravenous and oral probenecid and furosemide administration were gathered from literature and used for model development. For model evaluation, plasma concentration-time profiles, areas under the plasma concentration–time curve (AUC) and peak plasma concentrations (C_max) were predicted and compared to observed data. In addition, the models were applied to predict the outcome of clinical DDI studies.

Results

The developed models accurately describe the reported plasma concentrations of 27 clinical probenecid studies and of 42 studies using furosemide. Furthermore, application of these models to predict the probenecid-furosemide and probenecid-rifampicin DDIs demonstrates their good performance, with 6/7 of the predicted DDI AUC ratios and 4/5 of the predicted DDI C_max ratios within 1.25-fold of the observed values, and all predicted DDI AUC and C_max ratios within 2.0-fold.

Conclusions

Whole-body PBPK models of probenecid and furosemide were built and evaluated, providing useful tools to support the investigation of transporter mediated DDIs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11095-020-02964-z.

Pathophysiology of Diuretic Resistance and Its Implications for the Management of Chronic Heart Failure

Diuretic resistance implies a failure to increase fluid and sodium (Na+) output sufficiently to relieve volume overload, edema, or congestion, despite escalating doses of a loop diuretic to a ceiling level (80 mg of furosemide once or twice daily or greater in those with reduced glomerular filtration rate or heart failure). It is a major cause of recurrent hospitalizations in patients with chronic heart failure and predicts death but is difficult to diagnose unequivocally. Pharmacokinetic mechanisms include the low and variable bioavailability of furosemide and the short duration of all loop diuretics that provides time for the kidneys to restore diuretic-induced Na+ losses between doses. Pathophysiological mechanisms of diuretic resistance include an inappropriately high daily salt intake that exceeds the acute diuretic-induced salt loss, hyponatremia or hypokalemic, hypochloremic metabolic alkalosis, and reflex activation of the renal nerves. Nephron mechanisms include tubular tolerance that can develop even during the time that the renal tubules are exposed to a single dose of diuretic, or enhanced reabsorption in the proximal tubule that limits delivery to the loop, or an adaptive increase in reabsorption in the downstream distal tubule and collecting ducts that offsets ongoing blockade of Na+ reabsorption in the loop of Henle. These provide rationales for novel strategies including the concurrent use of diuretics that block these nephron segments and even sequential nephron blockade with multiple diuretics and aquaretics combined in severely diuretic-resistant patients with heart failure.

The role of solute carrier (SLC) transporters in actinomycin D pharmacokinetics in paediatric cancer patients

BACKGROUND

Actinomycin D is used for treatment of paediatric cancers; however, a large inter-patient pharmacokinetic (PK) variability and hepatotoxicity are significant limitations to its use and warrant further investigation. Elimination of actinomycin D may be mediated by transporters, as the drug does not seem to undergo significant metabolism. We investigated the role of solute carrier (SLC) transporters in actinomycin D PK.

METHODS

Fourteen key SLCs were screened through probe substrate uptake inhibition by actinomycin D in HEK293 cells. Uptake of actinomycin D was further studied in candidate SLCs by measuring intracellular actinomycin D using a validated LCMS assay. Pharmacogenetic analysis was conducted for 60 patients (Clinical trial: NCT00900354), who were genotyped for SNPs for OAT4 and PEPT2.

RESULTS

OAT4, OCT2, OCT3 and PEPT2 showed significantly lower probe substrate uptake (mean ± SD 75.0 ± 3.5% (p < 0.0001), 74.8 ± 11.2% (p = 0.001), 81.2 ± 14.0% (p = 0.0083) and 70.7 ± 5.7% (p = 0.0188)) compared to that of control. Intracellular accumulation of actinomycin D was greater compared to vector control in OAT4-transfected cells by 1.5- and 1.4-fold at 10 min (p = 0.01) and 20 min (p = 0.03), and in PEPT2-transfected cells by 1.5- and 1.7-fold at 10 min (p = 0.047) and 20 min (p = 0.043), respectively. Subsequent clinical study did not find a significant association between OAT4 rs11231809 and PEPT2 rs2257212 genotypes, and actinomycin D PK parameters such as clearance (CL) and volume of distribution (V_d).

CONCLUSION

Transport of actinomycin D was mediated by OAT4 and PEPT2 in vitro. There was a lack of clinical significance of OAT4 and PEPT2 genotypes as predictors of actinomycin D disposition in paediatric cancer patients.

Genetic Heterogeneity of SLC22 Family of Transporters in Drug Disposition

An important aspect of modern medicine is its orientation to achieve more personalized pharmacological treatments. In this context, transporters involved in drug disposition have gained well-justified attention. Owing to its broad spectrum of substrate specificity, including endogenous compounds and xenobiotics, and its strategical expression in organs accounting for drug disposition, such as intestine, liver and kidney, the SLC22 family of transporters plays an important role in physiology, pharmacology and toxicology. Among these carriers are plasma membrane transporters for organic cations (OCTs) and anions (OATs) with a marked overlap in substrate specificity. These two major clades of SLC22 proteins share a similar membrane topology but differ in their degree of genetic variability. Members of the OCT subfamily are highly polymorphic, whereas OATs have a lower number of genetic variants. Regarding drug disposition, changes in the activity of these variants affect intestinal absorption and target tissue uptake, but more frequently they modify plasma levels due to enhanced or reduced clearance by the liver and secretion by the kidney. The consequences of these changes in transport-associated function markedly affect the effectiveness and toxicity of the treatment in patients carrying the mutation. In solid tumors, changes in the expression of these transporters and the existence of genetic variants substantially determine the response to anticancer drugs. Moreover, chemoresistance usually evolves in response to pharmacological and radiological treatment. Future personalized medicine will require monitoring these changes in a dynamic way to adapt the treatment to the weaknesses shown by each tumor at each stage in each patient.

Renal Drug Transporters and Drug Interactions

Transporters in proximal renal tubules contribute to the disposition of numerous drugs. Furthermore, the molecular mechanisms of tubular secretion have been progressively elucidated during the past decades. Organic anions tend to be secreted by the transport proteins OAT1, OAT3 and OATP4C1 on the basolateral side of tubular cells, and multidrug resistance protein (MRP) 2, MRP4, OATP1A2 and breast cancer resistance protein (BCRP) on the apical side. Organic cations are secreted by organic cation transporter (OCT) 2 on the basolateral side, and multidrug and toxic compound extrusion (MATE) proteins MATE1, MATE2/2-K, P-glycoprotein, organic cation and carnitine transporter (OCTN) 1 and OCTN2 on the apical side. Significant drug-drug interactions (DDIs) may affect any of these transporters, altering the clearance and, consequently, the efficacy and/or toxicity of substrate drugs. Interactions at the level of basolateral transporters typically decrease the clearance of the victim drug, causing higher systemic exposure. Interactions at the apical level can also lower drug clearance, but may be associated with higher renal toxicity, due to intracellular accumulation. Whereas the importance of glomerular filtration in drug disposition is largely appreciated among clinicians, DDIs involving renal transporters are less well recognized. This review summarizes current knowledge on the roles, quantitative importance and clinical relevance of these transporters in drug therapy. It proposes an approach based on substrate-inhibitor associations for predicting potential tubular-based DDIs and preventing their adverse consequences. We provide a comprehensive list of known drug interactions with renally-expressed transporters. While many of these interactions have limited clinical consequences, some involving high-risk drugs (e.g. methotrexate) definitely deserve the attention of prescribers.

Recent advance in the pharmacogenomics of human Solute Carrier Transporters (SLCs) in drug disposition

Drug pharmacokinetics is influenced by the function of metabolising enzymes and influx/efflux transporters. Genetic variability of these genes is known to impact on clinical therapies. Solute Carrier Transporters (SLCs) are the primary influx transporters responsible for the cellular uptake of drug molecules, which consequently, impact on drug efficacy and toxicity. The Organic Anion Transporting Polypeptides (OATPs), Organic Anion Transporters (OATs) and Organic Cation Transporters (OCTs/OCTNs) are the most important SLCs involved in drug disposition. The information regarding the influence of SLC polymorphisms on drug pharmacokinetics is limited and remains a hot topic of pharmaceutical research. This review summarises the recent advance in the pharmacogenomics of SLCs with an emphasis on human OATPs, OATs and OCTs/OCTNs. Our current appreciation of the degree of variability in these transporters may contribute to better understanding the inter-patient variation of therapies and thus, guide the optimisation of clinical treatments.

Additive composite ABCG2, SLC2A9 and SLC22A12 scores of high-risk alleles with alcohol use modulate gout risk

The aim of the present study was to evaluate the contribution of urate transporter genes and alcohol use to the risk of gout/tophi. Eight variants of ABCG2, SLC2A9, SLC22A12, SLC22A11 and SLC17A3 were genotyped in male individuals in a case-control study with 157 gout (33% tophi), 106 asymptomatic hyperuricaemia and 295 control subjects from Taiwan. The multilocus profiles of the genetic risk scores for urate gene variants were used to evaluate the risk of asymptomatic hyperuricaemia, gout and tophi. ABCG2 Q141K (T), SLC2A9 rs1014290 (A) and SLC22A12 rs475688 (C) under an additive model and alcohol use independently predicted the risk of gout (respective odds ratio for each factor=2.48, 2.03, 1.95 and 2.48). The additive composite Q141K, rs1014290 and rs475688 scores of high-risk alleles were associated with gout risk (P<0.0001). We observed the supramultiplicative interaction effect of genetic urate scores and alcohol use on gout and tophi risk (P for interaction=0.0452, 0.0033). The synergistic effect of genetic urate score 5-6 and alcohol use indicates that these combined factors correlate with gout and tophi occurrence.

A pharmacogenetic investigation of intravenous furosemide in decompensated heart failure: a meta-analysis of three clinical trials

We conducted a meta-analysis of pharmacogenomic substudies of three randomized trials conducted in patients with decompensated heart failure (HF) that were led by National Heart Lung and Blood Institute (NHLBI)-funded HF Network to test the hypothesis that candidate genes modulate net fluid loss and weight change in patients with decompensated HF treated with a furosemide-based diuretic regimen. Although none of the genetic variants previously shown to modulate the effects of loop diuretics in healthy individuals were associated with net fluid loss after 72 h of treatment, a set of rare variants in the APOL1 gene, which codes for apolipoprotein L1 (P=0.0005 in the random effects model), was associated with this end point. Moreover, a common variant in the multidrug resistance protein-4 coding gene (ABCC4, rs17268282) was associated with weight loss with furosemide use (P=0.0001). Our results suggest that both common and rare genetic variants modulate the response to a furosemide-based diuretic regimen in patients with decompensated HF.

Role of OAT4 in Uptake of Estriol Precursor 16α-Hydroxydehydroepiandrosterone Sulfate Into Human Placental Syncytiotrophoblasts From Fetus

Estriol biosynthesis in human placenta requires the uptake of a fetal liver-derived estriol precursor, 16α-hydroxydehydroepiandrosterone sulfate (16α-OH DHEAS), by placental syncytiotrophoblasts at their basal plasma membrane (BM), which faces the fetal circulation. The aim of this work is to identify the transporter(s) mediating 16α-OH DHEAS uptake at the fetal side of syncytiotrophoblasts by using human placental BM-enriched vesicles and to examine the contribution of the putative transporter to estriol synthesis at the cellular level, using choriocarcinoma JEG-3 cells. Organic anion transporter (OAT)-4 and organic anion transporting polypeptide 2B1 proteins were enriched in human placental BM vesicles compared with crude membrane fraction. Uptake of [(3)H]16α-OH DHEAS by BM vesicles was partially inhibited in the absence of sodium but was significantly increased in the absence of chloride and after preloading glutarate. Uptake of [(3)H]16α-OH DHEAS by BM vesicles was significantly inhibited by OAT4 substrates such as dehydroepiandrosterone sulfate, estrone-3-sulfate, and bromosulfophthalein but not by cyclosporin A, tetraethylammonium, p-aminohippuric acid, or cimetidine. These characteristics of vesicular [(3)H]16α-OH DHEAS uptake are in good agreement with those of human OAT4-transfected COS-7 cells as well as forskolin-differentiated JEG-3 cells. Estriol secretion from differentiated JEG-3 cells was detected when the cells were incubated with 16α-OH DHEAS for 8 hours but was inhibited in the presence of 50 μM bromosulfophthalein. Our results indicate that OAT4 at the BM of human placental syncytiotrophoblasts plays a predominant role in the uptake of 16α-OH DHEAS for placental estriol synthesis.

Genetic polymorphisms in low-dose methotrexate transporters: current relevance as methotrexate therapeutic outcome biomarkers

Methotrexate (MTX) is used in low doses to treat a variety of diseases. Although the mechanism responsible for its therapeutic action is unknown, MTX membrane transport proteins (influx and/or efflux) can be major determinants of pharmacokinetics, adverse drug reactions and clinical response profiles. With progess in pharmacogenomics, the improvement of the prediction of patients' therapeutic outcome treated with low doses of MTX will offer a powerful tool for the translation of transporter SNPs into clinical practice and will be essential to sustain a breakthrough in the field of personalized medicine. Therefore, this paper provides an update on the current data on SNPs in genes encoding low-dose MTX membrane transport proteins and their relevance as possible biomarkers of MTX therapeutic outcome.

Pharmacogenomics of Methotrexate Membrane Transport Pathway: Can Clinical Response to Methotrexate in Rheumatoid Arthritis Be Predicted?

Background: Methotrexate (MTX) is widely used for rheumatoid arthritis (RA) treatment. Single nucleotide polymorphisms (SNPs) could be used as predictors of patients’ therapeutic outcome variability. Therefore, this study aims to evaluate the influence of SNPs in genes encoding for MTX membrane transport proteins in order to predict clinical response to MTX. Methods: Clinicopathological data from 233 RA patients treated with MTX were collected, clinical response defined, and patients genotyped for 23 SNPs. Genotype and haplotype analyses were performed using multivariate methods and a genetic risk index (GRI) for non-response was created. Results: Increased risk for non-response was associated to SLC22A11 rs11231809 T carriers; ABCC1 rs246240 G carriers; ABCC1 rs3784864 G carriers; CGG haplotype for ABCC1 rs35592, rs2074087 and rs3784864; and CGG haplotype for ABCC1 rs35592, rs246240 and rs3784864. GRI demonstrated that patients with Index 3 were 16-fold more likely to be non-responders than those with Index 1. Conclusions: This study revealed that SLC22A11 and ABCC1 may be important to identify those patients who will not benefit from MTX treatment, highlighting the relevance in translating these results to clinical practice. However, further validation by independent studies is needed to develop the field of personalized medicine to predict clinical response to MTX treatment.

Influence of ABCC2 and ABCC4 polymorphisms on tenofovir plasma concentrations in Thai HIV-infected patients

Tenofovir (TFV) is eliminated by renal excretion, which is mediated through multidrug-resistant protein 2 (MRP2) and MRP4, encoded by ABCC2 and ABCC4, respectively. Genetic polymorphisms of these transporters may affect the plasma concentrations of tenofovir. Therefore, the aim of this study was to investigate the influence of genetic and nongenetic factors on tenofovir plasma concentrations. A cross-sectional study was performed in Thai HIV-infected patients aged ≥18 years who had been receiving tenofovir disoproxil fumarate at 300 mg once daily for at least 6 months. A middose tenofovir plasma concentration was obtained. Multivariate analysis was performed to investigate whether there was an association between tenofovir plasma concentrations and demographic data, including age, sex, body weight, estimated glomerular filtration rate (eGFR), hepatitis B virus coinfection, hepatitis C virus coinfection, duration of tenofovir treatment, concomitant use of ritonavir-boosted protease inhibitors, and polymorphisms of ABCC2 and ABCC4. A total of 150 Thai HIV-infected patients were included. The mean age of the patients was 43.9 ± 7.2 years. The mean tenofovir plasma concentration was 100.3 ± 52.7 ng/ml. In multivariate analysis, a low body weight, a low eGFR, the concomitant use of ritonavir-boosted protease inhibitors, and the ABCC4 4131T → G variation (genotype TG or GG) were independently associated with higher tenofovir plasma concentrations. After adjusting for weight, eGFR, and the concomitant use of ritonavir-boosted protease inhibitors, a 30% increase in the mean tenofovir plasma concentration was observed in patients having the ABCC4 4131 TG or GG genotype. Both genetic and nongenetic factors affect tenofovir plasma concentrations. These factors should be considered when adjusting tenofovir dosage regimens to ensure the efficacy and safety of a drug. (This study has been registered at ClinicalTrials.gov under registration no. NCT01138241.).

Modeling the effects of commonly used drugs on human metabolism

Metabolism contributes significantly to the pharmacokinetics and pharmacodynamics of a drug. In addition, diet and genetics have a profound effect on cellular metabolism with respect to both health and disease. In the present study, we assembled a comprehensive, literature-based drug metabolic reconstruction of the 18 most highly prescribed drug groups, including statins, anti-hypertensives, immunosuppressants and analgesics. This reconstruction captures in detail our current understanding of their absorption, intracellular distribution, metabolism and elimination. We combined this drug module with the most comprehensive reconstruction of human metabolism, Recon 2, yielding Recon2_DM1796, which accounts for 2803 metabolites and 8161 reactions. By defining 50 specific drug objectives that captured the overall drug metabolism of these compounds, we investigated the effects of dietary composition and inherited metabolic disorders on drug metabolism and drug-drug interactions. Our main findings include: (a) a shift in dietary patterns significantly affects statins and acetaminophen metabolism; (b) disturbed statin metabolism contributes to the clinical phenotype of mitochondrial energy disorders; and (c) the interaction between statins and cyclosporine can be explained by several common metabolic and transport pathways other than the previously established CYP3A4 connection. This work holds the potential for studying adverse drug reactions and designing patient-specific therapies.

The SLC22 family with transporters of organic cations, anions and zwitterions

The SLC22 family contains 13 functionally characterized human plasma membrane proteins each with 12 predicted α-helical transmembrane domains. The family comprises organic cation transporters (OCTs), organic zwitterion/cation transporters (OCTNs), and organic anion transporters (OATs). The transporters operate as (1) uniporters which mediate facilitated diffusion (OCTs, OCTNs), (2) anion exchangers (OATs), and (3) Na(+)/zwitterion cotransporters (OCTNs). They participate in small intestinal absorption and hepatic and renal excretion of drugs, xenobiotics and endogenous compounds and perform homeostatic functions in brain and heart. Important endogeneous substrates include monoamine neurotransmitters, l-carnitine, α-ketoglutarate, cAMP, cGMP, prostaglandins, and urate. It has been shown that mutations of the SLC22 genes encoding these transporters cause specific diseases like primary systemic carnitine deficiency and idiopathic renal hypouricemia and are correlated with diseases such as Crohn's disease and gout. Drug-drug interactions at individual transporters may change pharmacokinetics and toxicities of drugs.

Reduced renal clearance of cefotaxime in asians with a low-frequency polymorphism of OAT3 (SLC22A8)

Organic anion transporter 3 (OAT3, SLC22A8), a transporter expressed on the basolateral membrane of the proximal tubule, plays a critical role in the renal excretion of organic anions including many therapeutic drugs. The goal of this study was to evaluate the in vivo effects of the OAT3-Ile305Phe variant (rs11568482), present at 3.5% allele frequency in Asians, on drug disposition with a focus on cefotaxime, a cephalosporin antibiotic. In HEK293-Flp-In cells, the OAT3-Ile305Phe variant had a lower maximum cefotaxime transport activity, Vmax , [159 ± 3 nmol*(mg protein)(-1) /min (mean ± SD)] compared with the reference OAT3 [305 ± 28 nmol*(mg protein)(-1) /min, (mean ± SD), p < 0.01], whereas the Michaelis-Menten constant values (Km ) did not differ. In healthy volunteers, we found volunteers that were heterozygous for the Ile305Phe variant and had a significantly lower cefotaxime renal clearance (CLR ; mean ± SD: 84.8 ± 32.1 mL/min, n = 5) compared with volunteers that were homozygous for the reference allele (158 ± 44.1 mL/min, n = 10; p = 0.006). Furthermore, the net secretory component of cefotaxime renal clearance (CLsec ) was reduced in volunteers heterozygous for the variant allele [33.3 ± 31.8 mL/min (mean ± SD)] compared with volunteers homozygous for the OAT3 reference allele [97.0 ± 42.2 mL/min (mean ± SD), p = 0.01]. In summary, our study suggests that a low-frequency reduced-function polymorphism of OAT3 associates with reduced cefotaxime CLR and CL(sec) .

A urate gene-by-diuretic interaction and gout risk in participants with hypertension: results from the ARIC study

OBJECTIVE

To test for a urate gene-by-diuretic interaction on incident gout.

METHODS

The Atherosclerosis Risk in Communities Study is a prospective population-based cohort of 15 792 participants recruited from four US communities (1987-1989). Participants with hypertension and available single nucleotide polymorphism (SNP) genotype data were included. A genetic urate score (GUS) was created from common urate-associated SNPs for eight genes. Gout incidence was self-reported. Using logistic regression, the authors estimated the adjusted OR of incident gout by diuretic use, stratified by GUS median.

RESULTS

Of 3524 participants with hypertension, 33% used a diuretic and 3.1% developed gout. The highest 9-year cumulative incidence of gout was in those with GUS above the median and taking a thiazide or loop diuretic (6.3%). Compared with no thiazide or loop diuretic use, their use was associated with an OR of 0.40 (95% CI 0.14 to 1.15) among those with a GUS below the median and 2.13 (95% CI 1.23 to 3.67) for those with GUS above the median; interaction p=0.006. When investigating the genes separately, SLC22A11 and SLC2A9 showed a significant interaction, consistent with the former encoding an organic anion/dicarboxylate exchanger, which mediates diuretic transport in the kidney.

CONCLUSIONS

Participants who were genetically predisposed to hyperuricaemia were susceptible to developing gout when taking thiazide or loop diuretics, an effect not evident among those without a genetic predisposition. These findings argue for a potential benefit of genotyping individuals with hypertension to assess gout risk, relative in part to diuretic use.

Pharmacogenetics in chronic heart failure: new developments and current challenges

The individual patient responses to chronic heart failure (HF) pharmacotherapies are highly variable. This variability cannot be entirely explained by clinical characteristics, and genetic variation may play a role. Therefore, this review will summarize the background pharmacogenetic literature for major HF pharmacotherapy classes (ie, β-blockers, angiotensin-converting enzyme inhibitors, digoxin, and loop diuretics), evaluate recent advances in the HF pharmacogenetic literature in the context of previous findings, and discuss the challenges and conclusions for HF pharmacogenetic data and its clinical application.

Association of intergenic polymorphism of organic anion transporter 1 and 3 genes with hypertension and blood pressure response to hydrochlorothiazide

BACKGROUND

Organic anion transporter (OAT) 1 and OAT3, encoded by a tightly linked gene pair, play a key role in renal secretion of diuretics. However, no study has yet examined the influence of OAT1 and OAT3 polymorphisms on high blood pressure (BP) and the response to thiazide diuretics. We hypothesized that intergenic polymorphisms between OAT1 and OAT3 might be associated with adult hypertension and the antihypertensive effects of hydrochlorothiazide (HCTZ).

METHODS

The association of an intergenic polymorphism (rs10792367) with hypertension risk was investigated in two independent case-control studies (n = 1,592 and 602), and then a combined analysis was performed for improving power (1,106 cases and 1,088 controls) with adjustment for geographic location. Two clinical trials (n = 542 and 274) were conducted in untreated hypertensive patients for the association of rs10792367 with antihypertensive responses to 4 and 8 weeks of HCTZ treatment.

RESULTS

No significant association was found between rs10792367 and hypertension after adjustment for conventional risk factors in either the two populations, respectively, or the combined two population. After adjustment for pretreatment BP and other confounders, HCTZ-induced reduction in systolic BP was 4.8 mm Hg (P = 0.006, first trial) and 6.1 mm Hg (P = 0.003, in second trial) lower, respectively, in C allele carriers than in GG carriers in the two clinical trials.

CONCLUSIONS

Intergenic polymorphism rs10792367 between OAT1 and OAT3 is not associated with hypertension, but appears to be involved in between-individual variations in antihypertensive responses to HCTZ.

Pharmacologic considerations for oseltamivir disposition: focus on the neonate and young infant

Across much of the world, pandemic H1N1 infection has produced a significant healthcare crisis, reflected in significant morbidity and mortality. Statistics reveal that infection-associated deaths among individuals without pre-existing conditions (e.g. immunosuppression) are clustered in pregnant women and young infants. In developing countries where the availability of influenzae vaccine is limited, the only currently available pharmacologic counter-measure for H1N1 disease is oseltamivir, a neuraminidase inhibitor with excellent in vitro activity against the virus. This drug is available in oral solid and liquid formulations, has excellent peroral bioavailability in adults, and generally has a very favorable safety profile. Many observational studies indicate that oseltamivir treatment is associated with symptomatic improvement in pediatric patients with H1N1 infection and, therefore, is considered to represent a viable therapeutic option for use in children. However, the disposition of the ethyl ester prodrug and its active metabolite has not been well characterized in infants and children. Presently, data are available from only two published investigations and preliminary summary information from a recent presentation of an ongoing study. Given that recent in vitro data support the importance of a target exposure-response profile for the active metabolite of oseltamivir and that many processes known to modulate drug disposition have a developmental basis, understanding the potential impact of age on oseltamivir disposition becomes crucial in the development of age-appropriate dosing regimens for the drug. In this review, the impact of ontogeny on processes that are important in regulating the absorption, distribution, metabolism, and excretion of oseltamivir and its active metabolite are considered. Data from both animal and human investigations are presented in the context of defining how development might influence the dose-exposure relationship and, most importantly, the significant variability associated with it. In addition, the available pediatric pharmacokinetic data for oseltamivir and its active metabolite are summarized and current 'information gaps' deserving of future study are presented.

New clues for nephrotoxicity induced by ifosfamide: preferential renal uptake via the human organic cation transporter 2

Anticancer treatment with ifosfamide but not with its structural isomer cyclophosphamide is associated with development of renal Fanconi syndrome leading to diminished growth in children and bone problems in adults. Since both cytotoxics share the same principal metabolites, we investigated whether a specific renal uptake of ifosfamide is the basis for this differential effect. First we studied the interaction of these cytotoxics using cells transfected with organic anion or cation transporters and freshly isolated murine and human proximal tubules with appropriate tracers. Next we determined changes in membrane voltage in proximal tubular cells to understand their differentiated nephrotoxicity. Ifosfamide but not cyclophosphamide was significantly transported into cells expressing human organic cation transporter 2 (hOCT2) while both did not interact with organic anion transporters. This points toward a specific interaction of ifosfamide with hOCT2, which is the main OCT isoform in human kidney. In isolated human proximal tubules ifosfamide also interacted with organic cation transport. This interaction was also seen in isolated mouse proximal tubules; however, it was absent in tubules from OCT-deficient mice, illustrating the biological importance of this selective transport. Ifosfamide decreased the viability of cells expressing hOCT2, but not that of control cells. Coadministration of cimetidine, a known competitive substrate of hOCT2, completely prevented this ifosfamide-induced toxicity. Finally, ifosfamide but not cyclophosphamide depolarized proximal tubular cells. We propose that the nephrotoxicity of ifosfamide is due to its selective uptake by hOCT2 into renal proximal tubular cells, and that coadministration of cimetidine may be used to prevent ifosfamide-induced nephrotoxicity.

Genetic variants of human organic anion transporter 4 demonstrate altered transport of endogenous substrates

Apical reabsorption from the urine has been shown to be important for such processes as the maintenance of critical metabolites in the blood and the excretion of nephrotoxic compounds. The solute carrier (SLC) transporter OAT4 (SLC22A11) is expressed on the apical membrane of renal proximal tubule cells and is known to mediate the transport of a variety of xenobiotic and endogenous organic anions. Functional characterization of genetic variants of apical transporters thought to mediate reabsorption, such as OAT4, may provide insight into the genetic factors influencing the complex pathways involved in drug elimination and metabolite reclamation occurring in the kidney. Naturally occurring genetic variants of OAT4 were identified in public databases and by resequencing DNA samples from 272 individuals comprising 4 distinct ethnic groups. Nine total nonsynonymous variants were identified and functionally assessed using uptake of three radiolabeled substrates. A nonsense variant, R48Stop, and three other variants (R121C, V155G, and V155M) were found at frequencies of at least 2% in an ethnic group specific fashion. The L29P, R48Stop, and H469R variants displayed a complete loss of function, and kinetic analysis identified a reduced V(max) in the common nonsynonymous variants. Plasma membrane levels of OAT4 protein were absent or reduced in the nonfunctional variants, providing a mechanistic reason for the observed loss of function. Characterization of the genetic variants of reabsorptive transporters such as OAT4 is an important step in understanding variability in tubular reabsorption with important implications in innate homeostatic processes and drug disposition.

Organic anion transporters: discovery, pharmacology, regulation and roles in pathophysiology

Our understanding of the mechanisms behind inter- and intra-patient variability in drug response is inadequate. Advances in the cytochrome P450 drug metabolizing enzyme field have been remarkable, but those in the drug transporter field have trailed behind. Currently, however, interest in carrier-mediated disposition of pharmacotherapeutics is on a substantial uprise. This is exemplified by the 2006 FDA guidance statement directed to the pharmaceutical industry. The guidance recommended that industry ascertain whether novel drug entities interact with transporters. This suggestion likely stems from the observation that several novel cloned transporters contribute significantly to the disposition of various approved drugs. Many drugs bear anionic functional groups, and thus interact with organic anion transporters (OATs). Collectively, these transporters are nearly ubiquitously expressed in barrier epithelia. Moreover, several reports indicate that OATs are subject to diverse forms of regulation, much like drug metabolizing enzymes and receptors. Thus, critical to furthering our understanding of patient- and condition-specific responses to pharmacotherapy is the complete characterization of OAT interactions with drugs and regulatory factors. This review provides the reader with a comprehensive account of the function and substrate profile of cloned OATs. In addition, a major focus of this review is on the regulation of OATs including the impact of transcriptional and epigenetic factors, phosphorylation, hormones and gender.

Functional characterization of nonsynonymous single nucleotide polymorphisms in the human organic anion transporter 4 (hOAT4)

BACKGROUND AND PURPOSE

The human organic anion transporter (hOAT) family of transmembrane carrier proteins mediate the cellular flux of anionic substances, including certain hormones and anti-cancer drugs. hOAT4 is highly expressed at the apical membrane of the renal tubular cell and facilitates drug re-absorption in the kidney. In the present study, the impact of 10 nonsynonymous single nucleotide polymorphisms (SNPs) of hOAT4 on transport function in COS-7 cells was characterized.

EXPERIMENTAL APPROACH

Transport uptake assay was used to assess the function of the variant transporters. Cell surface biotinylation and western blot analysis were used to investigate the expression characteristics of the transporter proteins. Comparative modelling was used to interpret the influence of nonsynonymous changes in terms of hOAT4 structure.

KEY RESULTS

Four naturally occurring hOAT4 variants (L29P, R48Y, V155G and T392I) exhibited a significant loss of function. Substitution of leucine-29, which is a conserved residue in OATs, with a proline residue, impaired the synthesis or the apparent stability of the transporter and membrane insertion was disrupted in the R48Y variant. In the case of the V155G and T392I variants, impaired function was due to decreased affinity of the transporter for oestrone sulphate and impaired transporter-substrate turnover respectively. The T392I variant was inhibited more extensively than the wild-type transporter by the cationic substrate tetraethyl ammonium.

CONCLUSIONS AND IMPLICATIONS

Several naturally occurring SNPs encode variant hOAT4s that may impair the renal tubular re-absorption of important drug substrates.

Functional characterization of nonsynonymous single nucleotide polymorphisms in the human organic anion transporter 4 (hOAT4)

BACKGROUND AND PURPOSE

The human organic anion transporter (hOAT) family of transmembrane carrier proteins mediate the cellular flux of anionic substances, including certain hormones and anti-cancer drugs. hOAT4 is highly expressed at the apical membrane of the renal tubular cell and facilitates drug re-absorption in the kidney. In the present study, the impact of 10 nonsynonymous single nucleotide polymorphisms (SNPs) of hOAT4 on transport function in COS-7 cells was characterized.

EXPERIMENTAL APPROACH

Transport uptake assay was used to assess the function of the variant transporters. Cell surface biotinylation and western blot analysis were used to investigate the expression characteristics of the transporter proteins. Comparative modelling was used to interpret the influence of nonsynonymous changes in terms of hOAT4 structure.

KEY RESULTS

Four naturally occurring hOAT4 variants (L29P, R48Y, V155G and T392I) exhibited a significant loss of function. Substitution of leucine-29, which is a conserved residue in OATs, with a proline residue, impaired the synthesis or the apparent stability of the transporter and membrane insertion was disrupted in the R48Y variant. In the case of the V155G and T392I variants, impaired function was due to decreased affinity of the transporter for oestrone sulphate and impaired transporter-substrate turnover respectively. The T392I variant was inhibited more extensively than the wild-type transporter by the cationic substrate tetraethyl ammonium.

CONCLUSIONS AND IMPLICATIONS

Several naturally occurring SNPs encode variant hOAT4s that may impair the renal tubular re-absorption of important drug substrates.

Identification of genetic polymorphisms of human OAT1 and OAT2 genes and their relationship to hOAT2 expression in human liver

BACKGROUND

Organic anion transporters (OATs) play an essential role in the disposition of numerous organic anions. To clarify the interindividual variation in the function of OATs, genetic polymorphisms of the SLC22A6 and SLC22A7 in Korean subjects were investigated and associated with hepatic hOAT2 expression and the SLC22A7 genotype.

METHODS

The genetic variants and their frequencies for the SLC22A6 and SLC22A7 genes in 50 Korean subjects were investigated by direct sequencing. The expression of hOAT2 protein from 34 human liver samples was examined by western blot analysis.

RESULTS

Eight SNPs including 2 novel SNPs were identified in the SLC22A6 gene and eight SNPs including 4 novel SNPs were identified in the SLC22A7 gene. No amino acid alteration was found. Linkage disequilibrium (LD) analysis revealed that the SLC22A6 and SLC22A7 genes have separated single LD blocks and consist of a limited number of haplotypes (14 haplotypes for SLC22A6 and 5 haplotypes for SLC22A7). The expression of the hOAT2 protein varied 10-fold among 34 human livers but was not associated with the SLC22A7 genotype (p=0.16).

CONCLUSIONS

The SLC22A7 genomic sequences showed low variability. A 10-fold variation in hOAT2 protein expression in the liver specimens was not correlated with SLC22A7 genotypes. These results suggest that genetic polymorphisms may not be a significant contributing factor to variations in the hOAT2 expression or hOAT2 transport activity.

The effects of genetic polymorphisms in the organic cation transporters OCT1, OCT2, and OCT3 on the renal clearance of metformin

Organic cation transporters (OCTs) can mediate metformin transmembrane transport. We explored metformin pharmacokinetics in relation to genetic variations in OCT1, OCT2, OCT3, OCTN1, and MATE1 in 103 healthy male Caucasians. Renal clearance varied 3.8-fold and was significantly dependent on creatinine clearance (r(2) = 0.42, P < 0.0001), age (r(2) = 0.09, P = 0.002), and OCT1 polymorphisms. Carriers of zero, one, and two low-activity OCT1 alleles (Arg61Cys, Gly401Ser, 420del, or Gly465Arg) had mean renal clearances of 30.6, 33.1, and 37.1 l/h, respectively (P = 0.04, after adjustment for creatinine clearance and age). Immunohistochemical staining of human kidneys demonstrated OCT1 expression on the apical side of proximal and distal tubules. Increased renal clearance, in parallel with the known decreased hepatic uptake, may contribute to reduced metformin efficacy in low-activity genotypes. Renal OCT1 expression may be important not only in relation to metformin but with respect to other drugs as well.

Determinants of steady-state torasemide pharmacokinetics: impact of pharmacogenetic factors, gender and angiotensin II receptor blockers

BACKGROUND

Torasemide is frequently used for the treatment of hypertension and heart failure. However, the determinants of torasemide pharmacokinetics in patients during steady-state conditions are largely unknown. We therefore explored the impact of genetic polymorphisms of cytochrome P450 (CYP) 2C9 (CYP2C9) and organic anion transporting polypeptide (OATP) 1B1 (SLCO1B1), gender, and the effects of losartan and irbesartan comedication on the interindividual variability of steady-state pharmacokinetics of torasemide.

PATIENTS AND METHODS

Twenty-four patients receiving stable medication with torasemide 10 mg once daily and with an indication for additional angiotensin II receptor blocker (ARB) treatment to control hypertension or to treat heart failure were selected. Blood samples were taken before torasemide administration and 0.5, 1, 2, 4, 8, 12 and 24 hours after administration. After this first study period, patients received either irbesartan 150 mg (five female and seven male patients aged 69+/-8 years) or losartan 100 mg (two female and ten male patients aged 61+/-8 years) once daily. After 3 days of ARB medication, eight blood samples were again collected at the timepoints indicated above. The patients' long-term medications, which did not include known CYP2C9 inhibitors, were maintained at a constant dose during the study. All patients were genotyped for CYP2C9 (*1/*1 [n=15]; *1/*2 [n = 4]; *1/*3 [n=5]) as well as for SLCO1B1 (c.521TT [n=13]; c.521TC [n=11]).

RESULTS

Factorial ANOVA revealed an independent impact of the CYP2C9 genotype (dose-normalized area under the plasma concentration-time curve during the 24-hour dosing interval at steady state [AUC(24,ss)/D]: *1/*1 375.5+/-151.4 microg x h/L/mg vs *1/*3 548.5+/-271.6 microg x h/L/mg, p=0.001), the SLCO1B1 genotype (AUC(24,ss)/D: TT 352.3+/-114 microg x h/L/mg vs TC 487.6+/-218.4 microg x h/L/mg, p<0.05) and gender (AUC(24,ss)/D: males 359.5+/-72.2 microg x h/L/mg vs females 547.3+/-284 microg x h/L/mg, p<0.01) on disposition of torasemide. Coadministration of irbesartan caused a 13% increase in the AUC(24,ss)/D of torasemide (p=0.002), whereas losartan had no effect.

CONCLUSION

This study shows that the CYP2C9*3 and SLCO1B1 c.521TC genotype and female gender are significant and independent predictors of the pharmacokinetics of torasemide. Coadministration of irbesartan yields moderate but significant increases in the torasemide plasma concentration and elimination half-life.

Effect of hypouricaemic and hyperuricaemic drugs on the renal urate efflux transporter, multidrug resistance protein 4

BACKGROUND AND PURPOSE

The xanthine oxidase inhibitors allopurinol and oxypurinol are used to treat hyperuricaemia, whereas loop and thiazide diuretics can cause iatrogenic hyperuricaemia. Some uricosuric drugs and salicylate have a bimodal action on urate renal excretion. The mechanisms of action of these hypo- and hyperuricaemic drugs on the handling of urate in renal tubules have not been fully elucidated. Recently, we identified the multidrug resistance protein (MRP) 4 as a luminal efflux transporter for urate in the proximal tubule.

EXPERIMENTAL APPROACH

Here, we studied the effect of these drugs on [(14)C]urate transport using human embryonic kidney 293 cells overexpressing human MRP4 and in membrane vesicles isolated from these cells.

KEY RESULTS

Allopurinol stimulated MRP4-mediated cellular urate efflux and allopurinol and oxypurinol both markedly stimulated urate transport by MRP4 in membrane vesicles. Bumetanide and torasemide had no effect, whereas furosemide, chlorothiazide, hydrochlorothiazide, salicylate, benzbromarone and sulfinpyrazone inhibited urate transport, at concentrations ranging from nanomolar up to millimolar. Probenecid stimulated urate transport at 0.1 microM and inhibited transport at higher concentrations.

CONCLUSIONS AND IMPLICATIONS

These data suggest that inhibition of MRP4-mediated urate efflux by furosemide and thiazide diuretics could have an important function in their hyperuricaemic mechanisms. Furthermore, stimulation of MRP4-mediated renal urate efflux could be a new mechanism in the hypouricaemic action of allopurinol and oxypurinol. In conclusion, MRP4 may provide a potential target for drugs affecting urate homoeostasis, which needs to be further evaluated in vivo.

Pharmacogenetics: data, concepts and tools to improve drug discovery and drug treatment

Variation in the human genome is a most important cause of variable response to drugs and other xenobiotics. Susceptibility to almost all diseases is determined to some extent by genetic variation. Driven by the advances in molecular biology, pharmacogenetics has evolved within the past 40 years from a niche discipline to a major driving force of clinical pharmacology, and it is currently one of the most actively pursued disciplines in applied biomedical research in general. Nowadays we can assess more than 1,000,000 polymorphisms or the expression of more than 25,000 genes in each participant of a clinical study -- at affordable costs. This has not yet significantly changed common therapeutic practices, but a number of physicians are starting to consider polymorphisms, such as those in CYP2C9, CYP2C19, CYP2D6, TPMT and VKORC1, in daily medical practice. More obviously, pharmacogenetics has changed the practices and requirements in preclinical and clinical drug research; large clinical trials without a pharmacogenomic add-on appear to have become the minority. This review is about how the discipline of pharmacogenetics has evolved from the analysis of single proteins to current approaches involving the broad analyses of the entire genome and of all mRNA species or all metabolites and other approaches aimed at trying to understand the entire biological system. Pharmacogenetics and genomics are becoming substantially integrated fields of the profession of clinical pharmacology, and education in the relevant methods, knowledge and concepts form an indispensable part of the clinical pharmacology curriculum and the professional life of pharmacologists from early drug discovery to pharmacovigilance.