Bilateral pharmacokinetic interaction between cyclosporine A and atorvastatin in renal transplant recipients

Cyclosporine A sterically inhibits statin transport by solute carrier OATP1B1

Members of the Organic Anion Transporter Polypeptides (OATP) are integral membrane proteins responsible for facilitating the transport of organic anions across the cell membrane. OATP1B1 (SLCO1B1), the prototypic OATP family member, is the most abundant uptake transporter in the liver and a key mediator of the hepatic uptake and clearance of numerous endogenous and xenobiotic compounds. It serves as a locus of important drug-drug interactions, such as those between statins and cyclosporine A, and carries the potential to enable liver-targeting therapeutics. In this study, we report cryo-EM structures of OATP1B1 and its complexes with one of its statin substrates, atorvastatin, and an inhibitor, cyclosporine A. This structural analysis has yielded insights into the mechanisms underlying the OATP1B1-mediated transport of statins and the inhibitory effect of cyclosporine A. These findings contribute to a better understanding of the molecular processes involved in drug transport and offer potential avenues for the development of targeted medications for liver-related conditions.

Assessing Trans-Inhibition of OATP1B1 and OATP1B3 by Calcineurin and/or PPIase Inhibitors and Global Identification of OATP1B1/3-Associated Proteins

Organic anion transporting polypeptide (OATP) 1B1 and OATP1B3 are key determinants of drug-drug interactions (DDIs). Various drugs including the calcineurin inhibitor (CNI) cyclosporine A (CsA) exert preincubation-induced trans-inhibitory effects upon OATP1B1 and/or OATP1B3 (abbreviated as OATP1B1/3) by unknown mechanism(s). OATP1B1/3 are phosphoproteins; calcineurin, which dephosphorylates and regulates numerous phosphoproteins, has not previously been investigated in the context of preincubation-induced trans-inhibition of OATP1B1/3. Herein, we compare the trans-inhibitory effects exerted on OATP1B1 and OATP1B3 by CsA, the non-analogous CNI tacrolimus, and the non-CNI CsA analogue SCY-635 in transporter-overexpressing human embryonic kidney (HEK) 293 stable cell lines. Preincubation (10-60 min) with tacrolimus (1-10 µM) rapidly and significantly reduces OATP1B1- and OATP1B3-mediated transport up to 0.18 ± 0.03- and 0.20 ± 0.02-fold compared to the control, respectively. Both CsA and SCY-635 can trans-inhibit OATP1B1, with the inhibitory effects progressively increasing over a 60 min preincubation time. At each equivalent preincubation time, CsA has greater trans-inhibitory effects toward OATP1B1 than SCY-635. Preincubation with SCY-635 for 60 min yielded IC50 of 2.2 ± 1.4 µM against OATP1B1, which is ~18 fold greater than that of CsA (0.12 ± 0.04 µM). Furthermore, a proteomics-based screening for protein interactors was used to examine possible proteins and processes contributing to OATP1B1/3 regulation and preincubation-induced inhibition by CNIs and other drugs. A total of 861 and 357 proteins were identified as specifically associated with OATP1B1 and OATP1B3, respectively, including various protein kinases, ubiquitin-related enzymes, the tacrolimus (FK506)-binding proteins FKBP5 and FKBP8, and several known regulatory targets of calcineurin. The current study reports several novel findings that expand our understanding of impaired OATP1B1/3 function; these include preincubation-induced trans-inhibition of OATP1B1/3 by the CNI tacrolimus, greater preincubation-induced inhibition by CsA compared to its non-CNI analogue SCY-635, and association of OATP1B1/3 with various proteins relevant to established and candidate OATP1B1/3 regulatory processes.

No Interference of H9 Extract on Trastuzumab Pharmacokinetics in Their Combinations

Trastuzumab is used to treat breast cancer patients overexpressing human epidermal growth factor receptor 2, but resistance and toxicity limit its uses, leading to attention to trastuzumab combinations. Recently, the synergistic effect of trastuzumab and H9 extract (H9) combination against breast cancer has been reported. Because drug exposure determines its efficacy and toxicity, the question of whether H9 changes trastuzumab exposure in the body has been raised. Therefore, this study aimed to characterize trastuzumab pharmacokinetics and elucidate the effect of H9 on trastuzumab pharmacokinetics at a combination dose that shows synergism in mice. As a result, trastuzumab showed linear pharmacokinetics after its intravenous administration from 1 to 10 mg/kg. In the combination of trastuzumab and H9, single and 2-week treatments of oral H9 (500 mg/kg) did not influence trastuzumab pharmacokinetics. In the multiple-combination treatments of trastuzumab and H9 showing their synergistic effect (3 weeks of trastuzumab with 2 weeks of H9), the pharmacokinetic profile of trastuzumab was comparable to that of 3 weeks of trastuzumab alone. In tissue distribution, the tissue to plasma ratios of trastuzumab below 1.0 indicated its limited distributions within the tissues, and these patterns were unaffected by H9. These results suggest that the systemic and local exposures of trastuzumab are unchanged by single and multiple-combination treatments of H9.

CYP3A5*3 and SLCO1B1 c.521T>C Polymorphisms Influence the Pharmacokinetics of Atorvastatin and 2-Hydroxy Atorvastatin

There is a large variability in individual responses to atorvastatin administration. This study assessed the pharmacogenetic effects of solute carrier organic anion transporter family member 1B1 (SLCO1B1, c.388A>G and c.521T>C) and cytochrome P450 3A5 (CYP3A5, CYP3A5*3) genetic polymorphisms on the pharmacokinetics of atorvastatin and its active metabolite, 2-hydroxy (2-OH) atorvastatin, in 46 individuals who were administered a clinically used single oral dosage of 80 mg. The Cmax and AUC of atorvastatin in CYP3A5*3/*3 carriers were 2.6- and 2.8-fold higher, respectively, than those in CYP3A5*1/*1 carriers, and similar results were observed for 2-OH atorvastatin pharmacokinetics. SLCO1B1 c.521T>C also increased the AUC of atorvastatin and 2-OH atorvastatin. The AUC ratio of atorvastatin and 2-OH atorvastatin were not affected by SLCO1B1 c.388A>G or c.521T>C, whereas CYP3A5*3 reduced the AUC ratio. In an analysis evaluating the simultaneous effect of the SLCO1B1 c.521T>C and CYP3A5*3 polymorphisms, SLCO1B1 c.521TT/CYP3A5*1/*1 carriers showed lower Cmax and AUC values for atorvastatin and 2-OH atorvastatin than in individuals with the SLCO1B1 c.521T>C and/or CYP3A5*3 genotypes. Among the participants with the SLCO1B1 c.521TT genotype, the CYP3A5*3 carriers had a higher systemic exposure to atorvastatin and 2-OH atorvastatin than the CYP3A5*1/*1 carriers. Thus, SLCO1B1 c.521T>C and CYP3A5*3 polymorphisms affect the pharmacokinetics of atorvastatin and 2-OH atorvastatin.

Current Evidence, Challenges, and Opportunities of Physiologically Based Pharmacokinetic Models of Atorvastatin for Decision Making

Atorvastatin (ATS) is the gold-standard treatment worldwide for the management of hypercholesterolemia and prevention of cardiovascular diseases associated with dyslipidemia. Physiologically based pharmacokinetic (PBPK) models have been positioned as a valuable tool for the characterization of complex pharmacokinetic (PK) processes and its extrapolation in special sub-groups of the population, leading to regulatory recognition. Several PBPK models of ATS have been published in the recent years, addressing different aspects of the PK properties of ATS. Therefore, the aims of this review are (i) to summarize the physicochemical and pharmacokinetic characteristics involved in the time-course of ATS, and (ii) to evaluate the major highlights and limitations of the PBPK models of ATS published so far. The PBPK models incorporate common elements related to the physicochemical aspects of ATS. However, there are important differences in relation to the analyte evaluated, the type and effect of transporters and metabolic enzymes, and the permeability value used. Additionally, this review identifies major processes (lactonization, P-gp contribution, ATS-Ca solubility, simultaneous management of multiple analytes, and experimental evidence in the target population), which would enhance the PBPK model prediction to serve as a valid tool for ATS dose optimization.

Pharmacogenetics of Statin-Induced Myotoxicity

Statins, a class of lipid-lowering medications, have been a keystone treatment in cardiovascular health. However, adverse effects associated with statin use impact patient adherence, leading to statin discontinuation. Statin-induced myotoxicity (SIM) is one of the most common adverse effects, prevalent across all ages, genders, and ethnicities. Although certain demographic cohorts carry a higher risk, the impaired quality of life attributed to SIM is significant. The pathogenesis of SIM remains to be fully elucidated, but it is clear that SIM is multifactorial. These factors include drug-drug interactions, renal or liver dysfunction, and genetics. Genetic-inferred risk for SIM was first reported by a landmark genome-wide association study, which reported a higher risk of SIM with a polymorphism in the SLCO1B1 gene. Since then, research associating genetic factors with SIM has expanded widely and has become one of the foci in the field of pharmacogenomics. This review provides an update on the genetic risk factors associated with SIM.

Prediction of Cyclosporin-Mediated Drug Interaction Using Physiologically Based Pharmacokinetic Model Characterizing Interplay of Drug Transporters and Enzymes

Uptake transporter organic anion transporting polypeptides (OATPs), efflux transporters (P-gp, BCRP and MRP2) and cytochrome P450 enzymes (CYP450s) are widely expressed in the liver, intestine or kidney. They coordinately work to control drug disposition, termed as "interplay of transporters and enzymes". Cyclosporine A (CsA) is an inhibitor of OATPs, P-gp, MRP2, BCRP and CYP3As. Drug-drug interaction (DDI) of CsA with victim drugs occurs via disordering interplay of transporters and enzymes. We aimed to establish a whole-body physiologically-based pharmacokinetic (PBPK) model which predicts disposition of CsA and nine victim drugs including atorvastatin, cerivastatin, pravastatin, rosuvastatin, fluvastatin, simvastatin, lovastatin, repaglinide and bosentan, as well as drug-drug interactions (DDIs) of CsA with nine victim drugs to investigate the integrated effect of enzymes and transporters in liver, intestinal and kidney on drug disposition. Predictions were compared with observations. Most of the predictions were within 0.5-2.0 folds of observations. Atorvastatin was represented to investigate individual contributions of transporters and CYP3As to atorvastatin disposition and their integrated effect. The contributions to atorvastatin disposition were hepatic OATPs >> hepatic CYP3A > intestinal CYP3As ≈ efflux transporters (P-gp/BCRP/MRP2). The results got the conclusion that the developed PBPK model characterizing the interplay of enzymes and transporters was successfully applied to predict the pharmacokinetics of 10 OATP substrates and DDIs of CsA with 9 victim drugs.

Species differences in the drug-drug interaction between atorvastatin and cyclosporine: In vivo study using a stable isotope-IV method in rats and dogs

In this study, drug-drug interaction (DDI) between atorvastatin (ATV) and cyclosporine (CsA) was kinetically analyzed using a stable isotope-IV method in rats and dogs. Obtained results were compared with the clinical data quoted from literatures to clarify the species difference in DDI both qualitatively and quantitatively. ATV only or ATV with CsA was orally administered to rats or dogs, and at 90 minutes after administration, a small amount of deuterium labeled ATV (ATV-d5) was intravenously injected. Assuming that ATV-d5 exhibits the same pharmacokinetic (PK) profile with ATV, PK parameters for absorption and elimination of ATV were calculated. Plasma levels of orally administered ATV were significantly enhanced by co-administration of CsA both in rats, dogs and humans, resulted in 9.8, 31, and 8.7-fold increase in systemic exposure calculated as AUC_po. High intensity of the DDI in dogs was mainly attributed to the marked decrease of the intrinsic hepatic clearance (to 1/10 of the control), which was induced by the inhibition of hepatic uptake of ATV via organic anion transporting polypeptide 1B1 (OATP1B1). CsA also affected the absorption of ATV form GI tract. Absorbed fraction of ATV into portal vein (calculated as F_a*F_g) was increased almost same extent in rats and dogs (around 3.0-fold) by co-administration of CsA. Inhibition of efflux transport via breast cancer resistance protein as well as the intestinal metabolism mediated by CYP enzymes contributed to the DDI occurred in the intestinal tract. In conclusion, PK analysis on the DDI between ATV and CsA in rats and dogs clearly demonstarted the factors to cause species differences in the extent of DDI. This type of quantitative analysis of DDIs in both small and large animals can be a great help to predict the extent of DDI in humans in the clinical study.

Interpretation of Drug Interaction Using Systemic and Local Tissue Exposure Changes

Systemic exposure of a drug is generally associated with its pharmacodynamic (PD) effect (e.g., efficacy and toxicity). In this regard, the change in area under the plasma concentration-time curve (AUC) of a drug, representing its systemic exposure, has been mainly considered in evaluation of drug-drug interactions (DDIs). Besides the systemic exposure, the drug concentration in the tissues has emerged as a factor to alter the PD effects. In this review, the status of systemic exposure, and/or tissue exposure changes in DDIs, were discussed based on the recent reports dealing with transporters and/or metabolic enzymes mediating DDIs. Particularly, the tissue concentration in the intestine, liver and kidney were referred to as important factors of PK-based DDIs.

Double trouble: ciclosporin-simvastatin coinduced rhabdomyolysis

A 73-year-old woman presented with an acute exacerbation of her long-standing psoriasis. Ciclosporin was commenced due to the severity of her symptoms resulting in remission within 2 weeks. Full blood count, urea and electrolytes following initiation of treatment were unremarkable, although she complained of muscle aches, which was attributed to her known multiple sclerosis. Three weeks later she was admitted to the hospital with diarrhoea and vomiting. Repeat blood tests revealed raised creatinine (528 μmol/L (normal range (NR) n=45-84 μmol/L)), urea (32.6 mmol/L (NR 2.5-7.8 mmol/L)) and creatine kinase (6792 IU/L (NR 25-200 IU/L)) levels and reduced estimated glomerular filtration rate of 7. A diagnosis of acute kidney injury secondary to rhabdomyolysis was made due to an interaction between ciclosporin and simvastatin, precipitated by the dehydration from gastroenteritis. Haemofiltration was required to stabilise her renal function and she made a complete recovery.

Clinical Controversy in Transplantation: Tacrolimus Versus Cyclosporine in Statin Drug Interactions

Objective: To review the available literature that provides evidence for the absence of statin interactions with tacrolimus compared with cyclosporine. Data Sources: A literature search of PubMed was performed (1990 to June 2019) using the following search terms: calcineurin inhibitors, tacrolimus, cyclosporine, statins, atorvastatin, simvastatin, and drug interactions. Clinical practice guidelines, article bibliographies, drug interaction database references, and product monographs were also reviewed. Study Selection and Data Extraction: Relevant English-language studies describing the mechanism of interaction, the magnitude of pharmacokinetic alterations, and safety were evaluated. In vitro data and studies conducted in adult humans were considered. Data Synthesis: Studies demonstrate pharmacokinetic differences between cyclosporine and tacrolimus, particularly with regard to inhibition of 2 hepatic transporters: P-glycoprotein and organic anion transporting polypeptide (OATP). Compared with cyclosporine, tacrolimus does not affect these transporters, does not enhance statin exposure, and does not increase statin-associated safety events. Relevance to Patient Care and Clinical Practice: Clinical practice guidelines allude to the need to reduce statin doses in the setting of tacrolimus. Some providers have adopted this practice, and doing so may prevent transplant recipients from attaining cardiovascular benefit, especially when increased or high-intensity doses are required. The pharmacokinetic differences between tacrolimus and cyclosporine highlight different interaction potential with statins. Conclusions: Clinicians need to be aware that tacrolimus and cyclosporine are not the same with regard to causing drug interactions with statins. Tacrolimus can be used with statins without the need for dose adjustments because of lack of an interaction.

Statin therapy for preventing cardiovascular diseases in patients treated with tacrolimus after kidney transplantation

Background

Lipid abnormalities are prevalent in tacrolimus-treated patients. The aim of the study was to evaluate the preventive effects of statin therapy on major adverse cardiovascular events (MACE) in patients treated with tacrolimus-based immunosuppression after kidney transplantation (KT), and to identify the risk factors.

Methods

This observational cohort study included adult patients who underwent KT and were treated with tacrolimus. Patients who received any lipid-lowering agents except statins, or had a history of immunosuppressant use before transplantation were excluded. The primary outcome was the adjusted risk of the first occurrence of MACE. The secondary outcomes included the risk of individual cardiovascular disease (CVD) and changes in cholesterol level. Subgroup analyses were performed in the statin-user group according to the dosage and/or type of statin.

Results

Compared with the control group (n=73), the statin-users (n=92) had a significantly reduced risk of MACE (adjusted HR, 0.31; 95% CI, 0.13–0.74). In the Cox regression analysis, old age, history of CVD, and comorbid hypertension were identified as independent factors associated with increased MACE. The total cholesterol levels were not significantly different between the two groups. Subjects with higher cumulative defined daily dose of statins had significantly lower risks of MACE.

Conclusion

Statin therapy in patients treated with tacrolimus after KT significantly lowered the risk of MACE. Long-term statin therapy is clearly indicated in older kidney transplant recipients for secondary prevention.

Importance of Hepatic Transporters in Clinical Disposition of Drugs and Their Metabolites

This review provides a practical clinical perspective on the relevance of hepatic transporters in pharmacokinetics and drug-drug interactions (DDIs). Special emphasis is placed on transporters with clear relevance to clinical DDIs, efficacy, and safety. Basolateral OATP1B1 and 1B3 emerged as important hepatic drug uptake pathways, sites for systemic DDIs, and sources of pharmacogenetic variability. As the first step in hepatic drug removal from the circulation, OATPs are an important determinant of systemic pharmacokinetics, specifically influencing systemic absorption, clearance, and hepatic distribution for subsequent metabolism and/or excretion. Biliary excretion of parent drugs is a less prevalent clearance pathway than metabolism or urinary excretion, but BCRP and MRP2 are critically important to biliary/fecal elimination of drug metabolites. Inhibition of biliary excretion is typically not apparent at the level of systemic pharmacokinetics but can markedly increase liver exposure. Basolateral efflux transporters MRP3 and MRP4 mediate excretion of parent drugs and, more commonly, polar metabolites from hepatocytes into blood. Basolateral excretion is an area in need of further clinical investigation, which will necessitate studies more complex than just systemic pharmacokinetics. Clinical relevance of hepatic uptake is relatively well appreciated, and clinical consequences of hepatic excretion (biliary and basolateral) modulation remain an active research area.

Statin use and hip fractures in U.S. kidney transplant recipients

Background

Basic and translational research supports beneficial effects of statins on bone metabolism. Clinical studies suggest that statin use may reduce the risk of hip fractures in the general population. Whether statin use is associated with hip fracture risk in kidney transplant recipients, a particularly high-risk group for this outcome, is unknown.

Methods

From the U.S. Renal Data System (2007–2011), we identified all hip fracture events recorded in Medicare billing claims of first-time kidney transplant recipients. We then matched all cases to an unlimited number of controls on age (±3 years), sex, race (black vs. non-black), and time since transplant. Cases and controls were required to have >1 year of Medicare Parts A + B + D coverage and be without a recorded history of hip fracture. We ascertained any statin use in the previous year and defined adherent statin use as those who had filled prescriptions for statins to cover >80% of days in that year (proportion of days covered, PDC). We ascertained several potential confounders (demographics, comorbidities, BMI, transplant-related factors) and applied conditional logistic regression with multiple imputation for missing data to estimate odds ratios (OR) and 95% confidence intervals (CI).

Results

We identified 231 hip fracture cases (mean age 51.8 years; 53% female; 11.3% black; 6.9 years from transplant, and 9.9 years from ESRD) and 15,575 matched controls. Any prior statin use was present in 64.1% of cases and 60.3% of controls with 37.2% of cases and 33.9% of controls being found adherent. Unadjusted conditional logistic regression showed an OR of 1.17 (0.89-1.54) for any statin use, and a fully-adjusted OR of 0.89 (0.67-1.19). Compared with statin non-users, the adjusted OR for patients with lesser adherence (PDC ≤80%) and those with greater adherence (PDC >80%) were 0.93 (0.66-1.31) and 0.87 (0.63-1.20), respectively.

Conclusion

Statin use was not associated with hip fracture risk in first-time kidney transplant recipients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12882-017-0559-9) contains supplementary material, which is available to authorized users.

Pediatric Statin Administration: Navigating a Frontier with Limited Data

Increasingly, children and adolescents with dyslipidemia qualify for pharmacologic intervention. As they are for adults, 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase inhibitors (statins) are the mainstay of pediatric dyslipidemia treatment when lifestyle modifications have failed. Despite the overall success of these drugs, the magnitude of variability in dose-exposure-response profiles contributes to adverse events and treatment failure. In children, the cause of treatment failures remains unclear. This review describes the updated guidelines for screening and management of pediatric dyslipidemia and statin disposition pathway to assist the provider in recognizing scenarios where alterations in dosage may be warranted to meet patients' specific needs.

Appropriate risk criteria for OATP inhibition at the drug discovery stage based on the clinical relevancy between OATP inhibitors and drug-induced adverse effect

DDI could be caused by the inhibition of OATP-mediated hepatic uptakes. The aim of this study is to set the risk criteria for the compounds that would cause DDI via OATP inhibition at the drug discovery stage. The IC₅₀ values of OATP inhibitors for human OATP-mediated atorvastatin uptake were evaluated in the expression system. In order to set the risk criteria for OATP inhibition, the relationship was clarified between OATP inhibitory effect and severe adverse effects of OATP substrates, rhabdomyolysis, hyperbilirubinemia and jaundice. Rhabdomyolysis would be caused in the atorvastatin AUC more than 9-fold of that at a minimum therapeutic dose. The atorvastatin AUC was 6- to 9-fold increased with the OATP inhibitors of which IC₅₀ values were ≤1 μmol/L. Hyperbilirubinemia and jaundice would be caused with the OATP inhibitors of which IC₅₀ values were ≤6 μmol/L. This investigation showed that the compounds with IC₅₀ of ≤1 μmol/L would have high risk for OATP-mediated DDI that would cause severe side effects. Before the detailed analysis based on the dosage, unbound fraction in blood and effective concentration to evaluate the clinical DDI potency, this criteria enable high throughput screening and optimize lead compounds at the drug discovery stage.

The association between atorvastatin administration and plasma total homocysteine levels in renal transplant recipients

BACKGROUND

Statins improve prognosis in patients with coronary heart diseases by decreasing the incidence of vascular events. Excess prevalence of hyperhomocysteinemia, an independent risk factor of cardiovascular diseases, has been observed in stable renal transplant recipients (RTRs).

OBJECTIVES

The objective of our study was to evaluate the association between atorvastatin administration and plasma total homocysteine (tHcy) levels in RTRs.

PATIENTS AND METHODS

We performed a retrospective cross-sectional study in 148 cyclosporine A (CsA) treated stable RTRs. We compared tHcy level and other demographic and clinical variables in RTRs with and without atorvastatin.

RESULTS

58.1% of the 148 RTRs were treated with atorvastatin (20-40 mg/day). Mean tHcy levels were lower in patients treated with atorvastatin compared to nonusers (14.80 ± 5.13 µmol/l versus 16.95 ± 7.87 µmol/l, P = 0.04). The comparison of 85 patients treated with atorvastatin and 61 non-users revealed that those subjects with atorvastatin were older, with higher estimated creatinine clearance and elevated body mass index (BMI). They were more likely to have higher systolic blood pressure and CsA trough level (C0). The association between lower tHcy levels and atorvastatin use was confirmed in the multivariate regression model (P = 0.004). However tHcy levels were independently and negatively associated with serum folate (P = 0.0001) and vitamin B12 levels (P = 0.001) and positively with serum BUN (P = 0.001) and diastolic blood pressure (P = 0.024) as well.

CONCLUSIONS

These data support the association between lower tHcy levels and atorvastatin administration in RTRs. Further clinical trials are recommended to clarify homocysteine lowering effect of atorvastatin.

Inhibition of OATP-1B1 and OATP-1B3 by tyrosine kinase inhibitors

BACKGROUND

The potential of tyrosine kinase inhibitors (TKIs) interacting with other therapeutics through hepatic uptake transporter inhibition has not been fully delineated in drug-drug interactions (DDIs). This study was designed to estimate the half-maximal inhibitory concentration (IC50) values of five small-molecule TKIs (pazopanib, nilotinib, vandetanib, canertinib and erlotinib) interacting with organic anion-transporting polypeptides (OATPs): OATP-1B1 and -1B3.

METHODS

The IC50 values of TKIs and rifampicin (positive control) were determined by concentration-dependent inhibition of TKIs on cellular accumulation of radiolabeled probe substrates [3H]estrone sulfate and [3H]cholecystokinin octapeptide. Chinese hamster ovary cells transfected with humanized OATP-1B1 and OATP-1B3 transporter proteins, respectively, were utilized to carry out these studies.

RESULTS

Pazopanib and nilotinib show inhibitory activity on OATP-1B1 transporter protein. IC50 values for rifampicin, pazopanib and nilotinib were 10.46±1.15, 3.89±1.21 and 2.78±1.13 μM, respectively, for OATP-1B1 transporter. Vandetanib, canertinib and erlotinib did not exhibit any inhibitory potency toward OATP-1B1 transporter protein. Only vandetanib expressed inhibitory potential toward OATP-1B3 transporter protein out of the five selected TKIs. IC50 values for rifampicin and vandetanib for OATP-1B3 transporter inhibition were 3.67±1.20 and 18.13±1.21 μM, respectively. No significant inhibition in the presence of increasing concentrations of pazopanib, nilotinib, canertinib and erlotinib were observed for OATP-1B3 transporter.

CONCLUSIONS

Because selected TKIs are inhibitors of OATP-1B1 and -1B3 expressed in hepatic tissue, these compounds can be regarded as molecular targets for transporter-mediated DDIs. These findings provide the basis for further preclinical and clinical studies investigating the transporter-based DDI potential of TKIs.

Increased dosage of cyclosporine induces myopathy with increased seru creatine kinase in an elderly patient on chronic statin therapy

WHAT IS KNOWN AND OBJECTIVE

The concomitant administration of atorvastatin and cyclosporine has been shown to increase the serum concentration of 3-hydroxy-3-methylglutaryl coenzyme A, which may be associated with the elevation of creatine kinase and an increased risk of myopathy. Our objective is to report on a case of statin-induced myopathy associated with concomitant use of cyclosporine and other contributing factors.

CASE SUMMARY

An 88-year-old Chinese male patient with comorbidities received polypharmacy treatment, including atorvastatin and cyclosporine. After the dosage of cyclosporine was increased to 300 mg every day for 8 months, the patient developed body pain and leg weakness, with a serum creatine kinase increase and evidence on magnetic resonance imaging of muscle oedema.

WHAT IS NEW AND CONCLUSION

Cyclosporine is a moderate inhibitor of the cytochrome P450 CYP3A4 isoenzyme, which is known to increase the serum level of atorvastatin. We hypothesized that the pharmacological and pharmacokinetic properties of atorvastatin-induced myopathy are the result of its interaction with high dosage of cyclosporine.

Hepatic uptake of atorvastatin: influence of variability in transporter expression on uptake clearance and drug-drug interactions

Differences in the expression and function of the organic anion transporting polypeptide (OATP) transporters contribute to interindividual variability in atorvastatin clearance. However, the importance of the bile acid transporter sodium taurocholate cotransporting polypeptide (NTCP, SLC10A1) in atorvastatin uptake clearance (CLupt) is not yet clarified. To elucidate this issue, we investigated the relative contribution of NTCP, OATP1B1, OATP1B3, and OATP2B1 to atorvastatin CLupt in 12 human liver samples. The impact of inhibition on atorvastatin CLupt was also studied, using inhibitors of different isoform specificities. Expression levels of the four transport proteins were quantified by liquid chromatography tandem mass spectrometry. These data, together with atorvastatin in vitro kinetics, were used to predict the maximal transport activity (MTA) and interindividual differences in CLupt of each transporter in vivo. Subsequently, hepatic uptake impairment on coadministration of five clinically interacting drugs was predicted using in vitro inhibitory potencies. NTCP and OATP protein expression varied 3.7- to 32-fold among the 12 sample donors. The rank order in expression was OATP1B1 > OATP1B3 ≈ NTCP ≈ OATP2B1. NTCP was found to be of minor importance in atorvastatin disposition. Instead, OATP1B1 and OATP1B3 were confirmed as the major atorvastatin uptake transporters. The average contribution to atorvastatin uptake was OATP1B1 > OATP1B3 >> OATP2B1 > NTCP, although this rank order varied among individuals. The interindividual differences in transporter expression and CLupt resulted in marked differences in drug-drug interactions due to isoform-specific inhibition. We conclude that this variation should be considered in in vitro to in vivo extrapolations.

Statin therapy is associated with the development of new-onset diabetes after transplantation in liver recipients with high fasting plasma glucose levels

New-onset diabetes after transplantation (NODAT) and dyslipidemia are important metabolic complications after liver transplantation (LT) that can adversely affect both allograft and patient survival. Statins are used as first-line therapies for dyslipidemia because of their effectiveness and safety profile. However, it has recently been reported that statin therapy is associated with new-onset diabetes in the nontransplant population. The aim of this study was to investigate the association between statin therapy and the development of NODAT in LT recipients. Three hundred sixty-four LT recipients who underwent transplantation between the ages of 20 and 75 years without a previous history of diabetes were enrolled in this study. We evaluated the incidence of NODAT with respect to statin use as well as other risk factors. The incidence of NODAT was significantly higher in the statin group (31.7%) versus the control group (17.6%, P = 0.03). The mean follow-up period was 37.8 ± 19.0 months for the statin group and 42.7 ± 16.0 months for the control group (P = 0.07). Statin use was significantly associated with NODAT development after adjustments for other risk factors [hazard ratio (HR) = 2.32, 95% confidence interval (CI) = 1.23-4.39, P = 0.01]. Impaired fasting glucose before transplantation was also a risk factor for NODAT development (HR = 2.21, 95% CI = 1.36-3.62, P = 0.001). There were no significant differences in age, body mass index, cumulative corticosteroid dose, or fasting plasma glucose (FPG) levels between the groups. Patients with high FPG levels were more likely to develop NODAT when they were placed on statins after LT (P = 0.002). In conclusion, statin treatment could contribute to the development of NODAT in LT recipients, especially if they have high baseline FPG levels.

Metabolic syndrome in children with chronic kidney disease and after renal transplantation

Visceral obesity and metabolic abnormalities typical for metabolic syndrome (MS) are the new epidemic in adolescence. MS is not only the risk factor for cardiovascular disease but also for chronic kidney disease (CKD). Thus, there are some reasons to recognize MS as a new challenge for pediatric nephrologists. First, hypertensive and diabetic nephropathy, the main causes of CKD in adults, both share the same pathophysiological abnormalities associated with visceral obesity and insulin resistance and have their origins in childhood. Secondly, as the obesity epidemic also affects children with CKD, MS emerges as the risk factor for progression of CKD. Thirdly, metabolic abnormalities typical for MS may pose additional risk for cardiovascular morbidity and mortality in children with CKD. Finally, although the renal transplantation reverses uremic abnormalities it is associated with an exposure to new metabolic risk factors typical for MS and MS has been found to be the risk factor for graft loss and cardiovascular morbidity after renal transplantation. MS is the result of imbalance between dietary energy intake and expenditure inducing disproportionate fat accumulation. Thus, the best prevention and treatment of MS is physical activity and maintenance of proper relationship between lean and fat mass.

Obesity, metabolic syndrome and diabetes mellitus after renal transplantation: prevention and treatment

The prevalence of the metabolic syndrome in dialysis patients is high and further increases after transplantation due to weight gain and the detrimental metabolic effects of immunosuppressive drugs. Corticosteroids cause insulin resistance, hyperlipidemia, abnormal glucose metabolism and arterial hypertension. The calcineurin inhibitor tacrolimus is diabetogenic by inhibiting insulin secretion, whereas cyclosporine causes hypertension and increases cholesterol levels. Mtor antagonists are responsible for hyperlipidemia and abnormal glucose metabolism by mechanisms that also implicate insulin resistance. The metabolic syndrome in transplant recipients has numerous detrimental effects such as increasing the risk of new onset diabetes, cardiovascular disease events and patient death. In addition, it has also been linked with accelerated loss of graft function, proteinuria and ultimately graft loss. Prevention and management of the metabolic syndrome are based on increasing physical activity, promotion of weight loss and control of cardiovascular risk factors. Bariatric surgery before or after renal transplantation in patients with body mass index >35 kg/m(2) is an option but its long term effects on graft and patient survival have not been investigated. Steroid withdrawal and replacement of tacrolimus with cyclosporine facilitate control of diabetes, whereas replacement of cyclosporine and mtor antagonists can improve hyperlipidemia. The new costimulation inhibitor belatacept has potent immunosuppressive properties without metabolic adverse effects and will be an important component of immunosuppressive regimens with better metabolic risk profile. Medical treatment of cardiovascular risk factors has to take potential drug interactions with immunosuppressive medication and drug accumulation due to renal insufficiency into account.

A common rejection module (CRM) for acute rejection across multiple organs identifies novel therapeutics for organ transplantation

A set of 11 genes, termed the common rejection module, predicts acute graft rejection in solid organ transplant patients and may help to identify novel drug targets in transplantation.

Using meta-analysis of eight independent transplant datasets (236 graft biopsy samples) from four organs, we identified a common rejection module (CRM) consisting of 11 genes that were significantly overexpressed in acute rejection (AR) across all transplanted organs. The CRM genes could diagnose AR with high specificity and sensitivity in three additional independent cohorts (794 samples). In another two independent cohorts (151 renal transplant biopsies), the CRM genes correlated with the extent of graft injury and predicted future injury to a graft using protocol biopsies. Inferred drug mechanisms from the literature suggested that two FDA-approved drugs (atorvastatin and dasatinib), approved for nontransplant indications, could regulate specific CRM genes and reduce the number of graft-infiltrating cells during AR. We treated mice with HLA-mismatched mouse cardiac transplant with atorvastatin and dasatinib and showed reduction of the CRM genes, significant reduction of graft-infiltrating cells, and extended graft survival. We further validated the beneficial effect of atorvastatin on graft survival by retrospective analysis of electronic medical records of a single-center cohort of 2,515 renal transplant patients followed for up to 22 yr. In conclusion, we identified a CRM in transplantation that provides new opportunities for diagnosis, drug repositioning, and rational drug design.

Interindividual variability in the hepatic expression of the human breast cancer resistance protein (BCRP/ABCG2): effect of age, sex, and genotype

Breast cancer resistance protein (BCRP), an efflux transporter expressed at the bile canalicular membrane, is responsible for the biliary clearance of many drugs. Data on the interindividual variability of hepatic BCRP expression are needed for in vitro to in vivo extrapolation of the biliary clearance of a BCRP substrate drug. Therefore, we measured the expression of BCRP in human livers (n = 65) by liquid chromatography coupled with tandem mass spectrometry. A calibration curve was generated using a synthetic signature peptide (SSLLDVLAAR) as the calibrator and the corresponding synthetic stable isotope-labeled peptide as the internal standard. The analytical method was accurate and precise. BCRP expression in 50 livers, where it was measurable, was 137.9 ± 42.1 atmol/µg of membrane protein (range 69.7-246.4 atmol/µg of membrane protein). BCRP expression was not associated with age (7-70 years), sex, or mRNA expression. BCRP expression in livers with the variant C421A (rs2231142) allele (14 heterozygotes, two homozygotes; among these, eight livers were below lower limit of quantification) was significantly lower than that in the wild-type livers (p < 0.002). Integration of these data with data on the hepatic expression of other transporters will allow refinement of physiologically based pharmacokinetic models to predict the pharmacokinetics, hepatic exposure, and drug-drug interactions of drugs (and/or their metabolites).

Evaluation of organic anion-transporting polypeptide 1B1 and CYP3A4 activities in primary human hepatocytes and HepaRG cells cultured in a dynamic three-dimensional bioreactor system

The long-term stability of liver cell functions is a major challenge when studying hepatic drug transport, metabolism, and toxicity in vitro. The aim of the present study was to investigate organic anion-transporting polypeptide (OATP) 1B1 and CYP3A4 activities in fresh primary human hepatocytes and differentiated cryopreserved HepaRG cells when cultured in a three-dimensional (3D) bioreactor system. OATP1B1 activity was determined by loss from media experiments of [(3)H]estradiol-17β-D-glucuronide and atorvastatin acid (ATA) for up to 7 days in culture. ATA metabolite formation was determined at days 3 to 4 to evaluate CYP3A4 activity. Overall, the results showed that freshly isolated human hepatocytes inoculated in the bioreactor retained OATP1B1 activity for at least 7 days, whereas in HepaRG cells no OATP1B1 activity was observed beyond day 2. The activity data were in agreement with immunohistochemical stainings, which showed that OATP1B1 protein expression was preserved for at least 9 days in fresh human hepatocytes, whereas OATP1B1 was expressed markedly lower in HepaRG cells after 9 days in culture. Fresh human hepatocytes and HepaRG cells exhibited similar CYP3A4 activity in bioreactor culture, and immunohistochemical stainings supported these findings. Activity and mRNA expression of OATP1B1 and CYP3A4 in primary human hepatocytes compared with HepaRG cells in fresh suspensions were in agreement with data obtained in bioreactor culture. In conclusion, freshly isolated human hepatocytes cultured in a 3D bioreactor system preserve both OATP1B1 and CYP3A4 activities, allowing long-term in vitro studies on drug disposition and toxicity.

Current understanding of hepatic and intestinal OATP-mediated drug-drug interactions

At present, many patients are medicated with various drugs, which are, at the same time, associated with an increased risk of drug-drug interactions (DDIs). Detailed analysis of mechanisms underlying DDIs is the basis of a better prediction of adverse drug events caused by drug interactions. In the last few decades, an involvement of transporters in such processes has been more and more recognized. Indeed, uptake transporters belonging to the organic anion-transporting polypeptide (OATP) family have been shown to interact with a variety of drugs in clinical use. Particularly, the subfamily of OATP1B transporters has been extensively studied, identifying several clinical significant DDIs based on those hepatic uptake transporters. By contrast, the role of OATP2B1 in this context is rather underestimated. Therefore, in addition to known interactions based on OATP1B transporters, we have focused on DDIs probably based on OATP2B1 inhibition in the liver and those possibly owing to the inhibition of OATP2B1-mediated drug absorption in the intestine.

In vitro evaluation of hepatic transporter-mediated clinical drug-drug interactions: hepatocyte model optimization and retrospective investigation

To assess the feasibility of using sandwich-cultured human hepatocytes (SCHHs) as a model to characterize transport kinetics for in vivo pharmacokinetic prediction, the expression of organic anion-transporting polypeptide (OATP) proteins in SCHHs, along with biliary efflux transporters, was confirmed quantitatively by liquid chromatography-tandem mass spectrometry. Rifamycin SV (Rif SV), which was shown to completely block the function of OATP transporters, was selected as an inhibitor to assess the initial rates of active uptake. The optimized SCHH model was applied in a retrospective investigation of compounds with known clinically significant OATP-mediated uptake and was applied further to explore drug-drug interactions (DDIs). Greater than 50% inhibition of active uptake by Rif SV was found to be associated with clinically significant OATP-mediated DDIs. We propose that the in vitro active uptake value therefore could serve as a cutoff for class 3 and 4 compounds of the Biopharmaceutics Drug Disposition Classification System, which could be integrated into the International Transporter Consortium decision tree recommendations to trigger clinical evaluations for potential DDI risks. Furthermore, the kinetics of in vitro hepatobiliary transport obtained from SCHHs, along with protein expression scaling factors, offer an opportunity to predict complex in vivo processes using mathematical models, such as physiologically based pharmacokinetics models.

In vitro and in silico strategies to identify OATP1B1 inhibitors and predict clinical drug-drug interactions

Purpose

To establish in vitro and in silico models that predict clinical drug–drug interactions (DDIs) with the OATP1B1 (SLCO1B1) transporter.

Methods

The inhibitory effect of 146 drugs and drug-like compounds on OATP1B1-mediated transport was studied in HEK293 cells. A computational model was developed to predict OATP1B1 inhibition. Concentration-dependent effects were investigated for six compounds; clinical DDIs were predicted by calculating change in exposure (i.e. R-values) in eight different ways.

Results

Sixty-five compounds were identified as OATP1B1 inhibitors at 20 μM. The computational model predicted the test set with 80% accuracy for inhibitors and 91% for non-inhibitors. In vitro–in vivo comparisons underscored the importance of using drugs with known clinical effects as references. Thus, reference drugs, cyclosporin A, gemfibrozil, and fenofibrate, provided an inhibition interval to which three antiviral drugs, atazanavir, lopinavir, and amprenavir, could be compared and their clinical DDIs with OATP1B1 classified.

Conclusions

Twenty-two new OATP1B1 inhibitors were identified, a predictive OATP1B1 inhibition in silico model was developed, and successful predictions of clinical DDIs were obtained with OATP1B1.

Use of transporter knockdown Caco-2 cells to investigate the in vitro efflux of statin drugs

The objective of the present study was to determine the efflux transporters responsible for acid and lactone statin drug efflux using transporter knockdown Caco-2 cells. The bidirectional transport was determined in Caco-2 cell monolayers in which the expression of P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), or multidrug resistance associated protein 2 (MRP2) was knocked down by transduction with lentivirus containing human transporter-targeted small hairpin RNAs (shRNAs). Cells transduced with lentivirus containing nontargeted shRNA served as the vector control. Atorvastatin, lovastatin, and rosuvastatin displayed extremely low apical-to-basolateral (A-to-B) transport, which made the P(app,A-B) values too unreliable to calculate the efflux ratio. Thus, transport comparisons were performed using the B-to-A permeability (P(app,B-A)) values. Presented in the order of vector control, P-gp, BCRP, and MRP2 knockdown Caco-2 cells, the P(app,B-A) values (×10(-6), cm/s) were 28.1 ± 1.3, 8.6 ± 2.9, 20.3 ± 1.8, and 21.5 ± 1.6 for atorvastatin; 96.1 ± 7.1, 25.3 ± 3.5, 57.3 ± 9.8, and 48.2 ± 2.3 for fluvastatin; and 14.1 ± 1.9, 4.6 ± 1.7, 5.8 ± 0.7, and 6.6 ± 1.8 for rosuvastatin, respectively. Lovastatin and simvastatin showed no efflux in the vector control or knockdown cell monolayers in either lactone or acid forms. Results indicate that atorvastatin, fluvastatin, and rosuvastatin were transported by P-gp, BCRP, and MRP2. On the other hand, neither the lactone nor the resulting acid of lovastatin and simvastatin was transported by P-gp, BCRP, or MRP2. The current study demonstrated that the transporter knockdown Caco-2 cells are useful tools for studying drug-transporter interactions and should help eliminate some of the ambiguity associated with the identification of drug-transporter interactions based on chemical inhibitors alone.

Organic anion transporting polypeptide 1B1: a genetically polymorphic transporter of major importance for hepatic drug uptake

The importance of membrane transporters for drug pharmacokinetics has been increasingly recognized during the last decade. Organic anion transporting polypeptide 1B1 (OATP1B1) is a genetically polymorphic influx transporter expressed on the sinusoidal membrane of human hepatocytes, and it mediates the hepatic uptake of many endogenous compounds and xenobiotics. Recent studies have demonstrated that OATP1B1 plays a major, clinically important role in the hepatic uptake of many drugs. A common single-nucleotide variation (coding DNA c.521T>C, protein p.V174A, rs4149056) in the SLCO1B1 gene encoding OATP1B1 decreases the transporting activity of OATP1B1, resulting in markedly increased plasma concentrations of, for example, many statins, particularly of active simvastatin acid. The variant thereby enhances the risk of statin-induced myopathy and decreases the therapeutic indexes of statins. However, the effect of the SLCO1B1 c.521T>C variant is different on different statins. The same variant also markedly affects the pharmacokinetics of several other drugs. Furthermore, certain SLCO1B1 variants associated with an enhanced clearance of methotrexate increase the risk of gastrointestinal toxicity by methotrexate in the treatment of children with acute lymphoblastic leukemia. Certain drugs (e.g., cyclosporine) potently inhibit OATP1B1, causing clinically significant drug interactions. Thus, OATP1B1 plays a major role in the hepatic uptake of drugs, and genetic variants and drug interactions affecting OATP1B1 activity are important determinants of individual drug responses. In this article, we review the current knowledge about the expression, function, substrate characteristics, and pharmacogenetics of OATP1B1 as well as its role in drug interactions, in parts comparing with those of other hepatocyte-expressed organic anion transporting polypeptides, OATP1B3 and OATP2B1.

Cyclosporine A, but not tacrolimus, shows relevant inhibition of organic anion-transporting protein 1B1-mediated transport of atorvastatin

The aim of this study was to investigate the potential of calcineurin inhibitors [cyclosporine A (CsA) and tacrolimus (Tac)] to inhibit cellular uptake of atorvastatin mediated by the liver-specific organic anion-transporting polypeptide 1B1 (OATP1B1) in vitro. Patients with solid organ transplants are frequently treated with HMG-CoA reductase inhibitors (statins). CsA increases atorvastatin systemic exposure severalfold, an effect not observed with Tac. The effect of CsA and Tac on atorvastatin transport via OATP1B1 was investigated in transfected human embryonic kidney 293 cells. An in vitro-in vivo extrapolation (IVIVE) was performed to estimate the clinical potential for CsA and Tac to inhibit OATP1B1-mediated transport. CsA inhibited OATP1B1-mediated uptake of atorvastatin approximately 90-fold more efficiently than Tac, with half-maximal inhibitory concentration (IC(50)) values of 0.021 +/- 0.004 and 1.99 +/- 0.42 muM, respectively. Coincubation compared with preincubation with CsA showed a 20-fold lower inhibitory capacity, with an IC(50) value of 0.47 +/- 0.34 muM. The IVIVE showed that clinically obtainable concentrations of CsA, but not Tac, inhibit OATP1B1 transport of atorvastatin. CsA inhibition ranged from 28 to 77% within a dosing interval, whereas it was less than 1% for Tac, considering free concentrations and assuming competitive inhibition. This does not fully explain the clinically observed interaction with CsA, suggesting that a more complex inhibitory mechanism may be present. This is also supported by the decreased IC(50) value of CsA after preincubation. This study provides evidence that OATP1B1 inhibition is a relevant mechanism for the interaction observed between CsA and atorvastatin.

Cardiovascular risk factors following orthotopic liver transplantation: predisposing factors, incidence and management

BACKGROUND

Liver transplantation is the standard of care for acute and chronic causes of end-stage liver disease. Advances in medical therapy and surgical techniques have led to improvement of patient and graft survival rates following orthotopic liver transplantation. However, the prevalence of post-transplant cardiovascular complications has been rising with increased life expectancy after liver transplantation.

AIMS

To determine the incidences, risk factors, and treatment for hypertension, hyperlipidaemia, diabetes, and obesity in the post-liver transplantation population.

METHODS

We performed a review of relevant studies available on the PubMed database that provided information on the incidence, risk factors and treatment for cardiovascular complications that develop in the post-liver transplantation population.

RESULTS

Current immunosuppressive agents have improved patient and graft survival rates. However, long-term exposure to these agents has been associated with development of systemic and metabolic complications including hypertension, hyperlipidaemia, diabetes mellitus and obesity. Cardiovascular disease remains one of the most common causes of death in liver transplant patients with functional grafts.

CONCLUSIONS

Liver transplant recipients have a higher risk of cardiovascular complications compared with the nontransplant population. Post-transplant cardiac risk stratification and aggressive treatment of cardiovascular complications, including modification of risk factors and tailoring of immunosuppressive regimen, is imperative to prevent serious complications.

P-glycoprotein related drug interactions: clinical importance and a consideration of disease states

IMPORTANCE OF THE FIELD

P-glycoprotein (P-gp) is the most characterized drug transporter in terms of its clinical relevance for pharmacokinetic disposition and interaction with other medicines. Clinically significant P-gp related drug interactions appear restricted to digoxin. P-gp may act as a major barrier to current and effective drug treatment in a number of diseases including cancer, AIDS, Alzheimer's and epilepsy due to its expression in tumors, lymphocytes, cell membranes of brain capillaries and the choroid plexus.

AREAS COVERED IN THIS REVIEW

This review summarizes the current understanding of P-gp structure/function, clinical importance of P-gp related drug interactions and the modulatory role this transporter may contribute towards drug efficacy in disease states such as cancer, AIDS, Alzheimer's and epilepsy.

WHAT THE READER WILL GAIN

The reader will gain an understanding that the clinical relevance of P-gp in drug interactions is limited. In certain disease states, P-gp in barrier tissues can modulate changes in regional distribution.

TAKE HOME MESSAGE

P-gp inhibition in isolation will not result in clinically important alterations in systemic exposure; however, P-gp transport may be of significance in barrier tissues (tumors, lymphocytes, brain) resulting in attenuated efficacy.

The use of hepatocytes to investigate drug uptake transporters

The liver plays an important role in the clearance of endogenous and exogenous compounds, including drugs. As hepatic uptake is the first step in hepatic clearance, any change in the former process directly affects the overall intrinsic hepatic clearance. Several uptake transporters are expressed on the basolateral membranes of hepatocytes and mediate the hepatic uptake of hydrophilic charged compounds that cannot easily penetrate the plasma membrane. As the substrate specificities of these individual drug transporters are broad and overlap, compounds are often recognized by multiple uptake transporters. Thus, knowledge of the contribution that each transporter makes to the hepatic uptake of a compound is important for predicting the extent to which hepatic uptake clearance will change if the activity of a specific transporter is altered by a genetic polymorphism or a drug-drug interaction. Human cryopreserved hepatocytes are now commercially available and can be used for studying hepatic uptake clearance. In this chapter, we describe a method for using isolated hepatocytes to estimate the in vivo uptake clearance of compounds and the quantitative contribution of each uptake transporter to the overall hepatic uptake of anionic compounds.