Drug-associated renal dysfunction and injury

High-throughput imaging-based nephrotoxicity prediction for xenobiotics with diverse chemical structures

The kidney is a major target for xenobiotics, which include drugs, industrial chemicals, environmental toxicants and other compounds. Accurate methods for screening large numbers of potentially nephrotoxic xenobiotics with diverse chemical structures are currently not available. Here, we describe an approach for nephrotoxicity prediction that combines high-throughput imaging of cultured human renal proximal tubular cells (PTCs), quantitative phenotypic profiling, and machine learning methods. We automatically quantified 129 image-based phenotypic features, and identified chromatin and cytoskeletal features that can predict the human in vivo PTC toxicity of 44 reference compounds with ~82 % (primary PTCs) or 89 % (immortalized PTCs) test balanced accuracies. Surprisingly, our results also revealed that a DNA damage response is commonly induced by different PTC toxicants that have diverse chemical structures and injury mechanisms. Together, our results show that human nephrotoxicity can be predicted with high efficiency and accuracy by combining cell-based and computational methods that are suitable for automation.

Drug-related acute renal failure in hospitalised patients

INTRODUCTION

The information available on the incidence and the characteristics of patients with acute renal failure (ARF) related to drugs is scarce.

OBJECTIVES

To estimate the incidence of drug-related ARF in hospitalised patients and to compare their characteristics with those of patients with ARF due to other causes.

MATERIAL AND METHODS

We selected a prospective cohort of patients with ARF during hospital admission (July 2010-July 2011). Information on patients' demographics, medical antecedents, ARF risk factors, ARF severity according to the RIFLE classification and hospital drug administration was collected. We analysed the relationship of drugs with the ARF episodes using Spanish Pharmacovigilance System methods and algorithm.

RESULTS

A total of 194 cases had an episode of hospital-acquired ARF. The median age of patients was 72 years [IQR 20]; 60% were men. The ARF incidence during hospitalization was 9.6 per 1,000 admissions. According to the RIFLE classification, a risk of kidney damage or kidney injury was present in 77.8% of cases. In 105 (54.1%) cases, ARF was drug-related; the drugs most frequently involved were diuretics, agents acting on the renin-angiotensin system, immunosuppressants, β-blocking agents, calcium channel blockers, contrast media and non-steroid anti-inflammatory drugs. Patients with drug-related ARF had more multi-morbidity, fewer ARF risk factors and lower mortality.

CONCLUSIONS

Half of ARF episodes during hospitalisation were drug related. Patients with drug-related ARF had higher cardiovascular morbidity than those with ARF related to other causes, but they had a lower frequency of ARF risk factors and mortality.

Integrated transcriptomic and proteomic analyses uncover regulatory roles of Nrf2 in the kidney

The transcription factor Nrf2 exerts protective effects in numerous experimental models of acute kidney injury, and is a promising therapeutic target in chronic kidney disease. To provide a detailed insight into the regulatory roles of Nrf2 in the kidney, we performed integrated transcriptomic and proteomic analyses of kidney tissue from wild-type and Nrf2 knockout mice treated with the Nrf2 inducer methyl-2-cyano-3,12-dioxooleano-1,9-dien-28-oate (CDDO-Me, also known as bardoxolone methyl). After 24 hours, analyses identified 2561 transcripts and 240 proteins that were differentially expressed in the kidneys of Nrf2 knockout mice, compared to wild-type counterparts, and 3122 transcripts and 68 proteins that were differentially expressed in wild-type mice treated with CDDO-Me, compared to vehicle control. In light of their sensitivity to genetic and pharmacological modulation of renal Nrf2 activity, genes/proteins that regulate xenobiotic disposition, redox balance, the intra/extracellular transport of small molecules, and the supply of NADPH and other cellular fuels were found to be positively regulated by Nrf2 in the kidney. This was verified by qPCR, immunoblotting, pathway analysis and immunohistochemistry. In addition, the levels of NADPH and glutathione were found to be significantly decreased in the kidneys of Nrf2 knockout mice. Thus, Nrf2 regulates genes that coordinate homeostatic processes in the kidney, highlighting its potential as a novel therapeutic target.

[Mechanism of Platinum Derivatives Induced Kidney Injury]

Platinum derivatives are the most widely used chemotherapeutic agents to treat solid tumors including ovarian, head and neck, and testicular germ cell tumors, lung cancer, and colorectal cancer. Two major problems exist, however, in the clinic use of platinum derivatives. One is the development of tumor resistance to the drug during therapy, leading to treatment failure. The other is the drug's toxicity such as the cisplatin's nephrotoxicity, which limits the dose that can be administered. This paper describes the mechanism of platinum derivatives induced kidney injury.

Drug-Induced Nephrotoxicity and Dose Adjustment Recommendations: Agreement Among Four Drug Information Sources

Hospitalized patients require the use of a variety of drugs, many of which individually or in combination have the potential to cause kidney damage. The use of potentially nephrotoxic drugs is often unavoidable, and the need for dose adjustment should be evaluated. This study is aimed at assessing concordance in information on drug-induced nephrotoxicity and dose adjustment recommendations by comparing four drug information sources (DRUGDEX^®, UpToDate^®, Medscape^® and the Brazilian Therapeutic Formulary) using the formulary of a Brazilian public hospital. A total of 218 drugs were investigated. The global Fleiss’ kappa coefficient was 0.265 for nephrotoxicity (p < 0.001; CI 95%, 0.211–0.319) and 0.346 for recommendations (p < 0.001; CI 95%, 0.292–0.401), indicating fair concordance among the sources. Anti-infectives and anti-hypertensives were the main drugs cited as nephrotoxic by the different sources. There were no clear definitions for qualitative data or quantitative values for dose adjustments among the four information sources. There was no advice for dosing for a large number of the drugs in the international databases. The National Therapeutic Formulary offered imprecise dose adjustment recommendations for many nephrotoxic drugs. Discrepancies among information sources may have a clinical impact on patient care and contribute to drug-related morbidity and mortality.

Effect of cisplatin on proteasome activity

Cisplatin is a widely used chemotherapy drug which exerts cytotoxic activity by affecting both nuclear and cytosolic pathways. Herewith, we report, for the first time, that cisplatin inhibits proteasome activity in vitro. Cisplatin induces a dose dependent inhibition of the three enzymatic activities of proteasome (i.e., the chymotrypsin-like activity, the trypsin-like activity and the caspase-like activity). Moreover, cisplatin administration to neuroblastoma cells brings about a fast loss of proteasome particle activity, which is followed by a de novo synthesis of proteasome. Lastly, we report that the simultaneous administration of lactacystin and cisplatin enhances the cytotoxicity of cisplatin alone. The overall bulk of data opens to an intriguing scenario, concerning the biological effects of cisplatin in the control of cellular life, which goes beyond the well established genotoxic effect.

Drug-induced renal disorders

Drug-induced nephrotoxicity are more common among infants and young children and in certain clinical situations such as underlying renal dysfunction and cardiovascular disease. Drugs can cause acute renal injury, intrarenal obstruction, interstitial nephritis, nephrotic syndrome, and acid-base and fluid electrolytes disorders. Certain drugs can cause alteration in intraglomerular hemodynamics, inflammatory changes in renal tubular cells, leading to acute kidney injury (AKI), tubulointerstitial disease and renal scarring. Drug-induced nephrotoxicity tends to occur more frequently in patients with intravascular volume depletion, diabetes, congestive heart failure, chronic kidney disease, and sepsis. Therefore, early detection of drugs adverse effects is important to prevent progression to end-stage renal disease. Preventive measures requires knowledge of mechanisms of drug-induced nephrotoxicity, understanding patients and drug-related risk factors coupled with therapeutic intervention by correcting risk factors, assessing baseline renal function before initiation of therapy, adjusting the drug dosage and avoiding use of nephrotoxic drug combinations

Beneficial effects of fermented black ginseng and its ginsenoside 20(S)-Rg3 against cisplatin-induced nephrotoxicity in LLC-PK1 cells

Background

Nephrotoxicity is a common side effect of medications. Panax ginseng is one of the best-known herbal medicines, and its individual constituents enhance renal function. Identification of its efficacy and mechanisms of action against drug-induced nephrotoxicity, as well as the specific constituents mediating this effect, have recently emerged as an interesting research area focusing on the kidney protective efficacy of P. ginseng.

Methods

The present study investigated the kidney protective effect of fermented black ginseng (FBG) and its active component ginsenoside 20(S)-Rg3 against cisplatin (chemotherapy drug)-induced damage in pig kidney (LLC-PK1) cells. It focused on assessing the role of mitogen-activated protein kinases as important mechanistic elements in kidney protection.

Results

The reduced cell viability induced by cisplatin was significantly recovered with FBG extract and ginsenoside 20(S)-Rg3 dose-dependently. The cisplatin-induced elevated protein levels of phosphorylated c-Jun N-terminal kinase (JNK), p53, and cleaved caspase-3 were decreased after cotreatment with FBG extract or ginsenoside 20(S)-Rg3. The elevated percentage of apoptotic LLC-PK1 cells induced by cisplatin treatment was significantly abrogated by cotreatment with FBG and the ginsenoside 20(S)-Rg3.

Conclusion

FBG and its major ginsenoside 20(S)-Rg3, ameliorated cisplatin-induced nephrotoxicity in LLC-PK1 cells by blocking the JNK–p53–caspase-3 signaling cascade.

A novel TXNIP-based mechanism for Cx43-mediated regulation of oxidative drug injury

Gap junctions (GJs) play an important role in the regulation of cell response to many drugs. However, little is known about their mechanisms. Using an in vitro model of cytotoxicity induced by geneticin (G418), we explored the potential signalling mechanisms involved. Incubation of cells with G418 resulted in cell death, as indicated by the change in cell morphology, loss of cell viability and activation of caspase-3. Before the onset of cell injury, G418 induced reactive oxygen species (ROS) generation, activated oxidative sensitive kinase P38 and caused a shift of connexin 43 (Cx43) from non-phosphorylated form to hyperphosphorylated form. These changes were largely prevented by antioxidants, suggesting an implication of oxidative stress. Downregulation of Cx43 with inhibitors or siRNA suppressed the expression of thioredoxin-interacting protein (TXNIP), activated Akt and protected cells against the toxicity of G418. Further analysis revealed that inhibition of TXNIP with siRNA activated Akt and reproduced the protective effect of Cx43-inhibiting agents, whereas suppression of Akt sensitized cells to the toxicity of G418. Furthermore, interference of TXNIP/Akt also affected puromycin- and adriamycin-induced cell injury. Our study thus characterized TXNIP as a presently unrecognized molecule implicated in the regulatory actions of Cx43 on oxidative drug injury. Targeting Cx43/TXNIP/Akt signalling cascade might be a promising approach to modulate cell response to drugs.

Expression of the Mre11-Rad50-Nbs1 complex in cisplatin nephrotoxicity

The aim of this study was to explore whether the Mre11, Rad50, and Nbs1 (MRN) complex is associated with DNA repair mechanisms in cisplatin-induced acute renal failure. Rats were randomly allocated into three groups: control, sacrificed 5 days (5D), and 10 days (10D) after 5mg/kg of cisplatin injection. The 5D group showed disrupted renal function together with enhanced MRN complex- and DNA repair-related protein expression. Meanwhile, in the 10D group, recovery from cisplatin-induced damage was accompanied by the reduced MRN expression, although the expression was still distinctive in proximal tubular cells and higher than the control group. Moreover, pretreatment with mirin, an MRN complex inhibitor, decreased cell viability and inhibited proliferating cell nuclear antigen expression in cisplatin-treated human embryonic kidney 293 cells. Taken together, cisplatin treatment could trigger the MRN complex expression in the kidney and inhibition of the complex might aggravate damage recovery processes.

Acute oral toxicity and biodistribution study of zinc-aluminium-levodopa nanocomposite

Layered double hydroxide (LDH) is an inorganic-organic nano-layered material that harbours drug between its two-layered sheets, forming a sandwich-like structure. It is attracting a great deal of attention as an alternative drug delivery (nanodelivery) system in the field of pharmacology due to their relative low toxic potential. The production of these nanodelivery systems, aimed at improving human health through decrease toxicity, targeted delivery of the active compound to areas of interest with sustained release ability. In this study, we administered zinc-aluminium-LDH-levodopa nanocomposite (ZAL) and zinc-aluminium nanocomposite (ZA) to Sprague Dawley rats to evaluate for acute oral toxicity following OECD guidelines. The oral administration of ZAL and ZA at a limit dose of 2,000 mg/kg produced neither mortality nor acute toxic signs throughout 14 days of the observation. The percentage of body weight gain of the animals showed no significant difference between control and treatment groups. Animal from the two treated groups gained weight continuously over the study period, which was shown to be significantly higher than the weight at the beginning of the study (P < 0.05). Biochemical analysis of animal serum showed no significant difference between rats treated with ZAL, ZA and controls. There was no gross lesion or histopathological changes observed in vital organs of the rats. The results suggested that ZAL and ZA at 2,000 mg/kg body weight in rats do not induce acute toxicity in the animals. Elemental analysis of tissues of treated animals demonstrated the wider distribution of the nanocomposite including the brain. In summary, findings of acute toxicity tests in this study suggest that zinc-aluminium nanocomposite intercalated with and the un-intercalated were safe when administered orally in animal models for short periods of time. It also highlighted the potential distribution ability of Tween-80 coated nanocomposite after oral administration.

Evaluation of Sub-acute Oral Toxicity of Lithium Carbonate Microemulsion (Nano Size) on Liver and Kidney of Mice

Background:

The development of drug delivery systems has improved the therapeutic and toxic properties of existing drugs in therapy. Microemulsion systems are novel vehicles for drug delivery, which have been developed in recent years. These systems are currently of interest to the pharmaceutical scientist because of their considerable potential to act as drug delivery vehicles by incorporating into a wide range of drug molecules. Although these systems improved solubility and bioavailability of drugs, they may have potential toxic effects on the body organs.

Objectives:

The purpose of this study was to examine a possible hepatotoxic and nephrotoxic effect of lithium carbonate microemulsion (LCME) in a mice model.

Materials and Methods:

Eighty male Swiss albino mice were randomly allocated to eight experimental groups, as follows: Group 1, as negative control group were treated orally with normal saline (0.9% NaCl); Group 2, received microemulsion base without drug as control group; Groups 3 to 5, received lithium carbonate (LC) solution in doses of 50, 100, and 200 mg/kg, respectively; Groups 6 to 8, received LCME orally in doses of 50, 100, and 200 mg/kg, respectively. All drugs were administered orally for ten consecutive days. Serum glutamate pyruvate aminotransferase (SGPT), serum glutamate oxaloacetate aminotransferase (SGOT), alkaline phosphatase (ALP), blood urea nitrogen (BUN), and plasma creatinine (Cr), as markers of liver and kidney toxicity in treated mice, were measured. Furthermore, the changes of tissue were assessed by histopathologic examination.

Results:

The findings showed that serum activity of ALP, SGOT, and SGPT and the levels of BUN and Cr in microemulsion base group was greater than normal saline group. However, this difference was not significant. Administration of LC and LCME in all doses resulted in a significant increase in the levels of BUN and serum activity of SGOT and SGPT in comparison to normal saline group (P < 0.05). Histopathological changes were observed in mice treated with LC or LCME.

Conclusions:

This study showed that subacute oral administration of different doses of LCME with severe toxicity in comparison to the same dose of LC.

Targeted therapy of colorectal neoplasia with rapamycin in peptide-labeled pegylated octadecyl lithocholate micelles

Many powerful drugs have limited clinical utility because of poor water solubility and high systemic toxicity. Here, we formulated a targeted nanomedicine, rapamycin encapsulated in pegylated octadecyl lithocholate micelles labeled with a new ligand for colorectal neoplasia, LTTHYKL peptide. CPC;Apc mice that spontaneously develop colonic adenomas were treated with free rapamycin, plain rapamycin micelles, and peptide-labeled rapamycin micelles via intraperitoneal injection for 35days. Endoscopy was performed to monitor adenoma regression in vivo. We observed complete adenoma regression at the end of therapy. The mean regression rate for peptide-labeled rapamycin micelles was significantly greater than that for plain rapamycin micelles, P<0.01. On immunohistochemistry, we observed a significant reduction in phospho-S6 but not β-catenin expression and reduced tumor cell proliferation, suggesting greater inhibition of downstream mTOR signaling. We observed significantly reduced renal toxicity for peptide-labeled rapamycin micelles compared to that of free drug, and no other toxicities were found on chemistries. Together, this unique targeted micelle represents a potential therapeutic for colorectal neoplasia with comparable therapeutic efficacy to rapamycin free drug and significantly less systemic toxicity.

Renal studies in safety pharmacology and toxicology: A survey conducted in the top 15 pharmaceutical companies

INTRODUCTION

With the recent development of more sensitive biomarkers to assess kidney injury preclinically, a survey was designed i) to investigate what strategies are used to investigate renal toxicity in both ICH S7A compliant Safety Pharmacology (SP) studies after a single dose of a compound and within repeat-dose toxicity studies by large pharmaceutical companies today; ii) to understand whether renal SP studies have impact or utility in drug development and/or if it may be more appropriate to assess renal effects after multiple doses of compounds; iii) to ascertain how much mechanistic work is performed by the top 15 largest pharmaceutical companies (as determined by R&D revenue size); iv) to gain an insight into the impact of the validation of DIKI biomarkers and their introduction in the safety evaluation paradigm; and v) to understand the impact of renal/urinary safety study data on progression of projects.

METHODS

Two short anonymous surveys were submitted to SP leaders of the top 15 pharmaceutical companies, as defined by 2012 R&D portfolio size. Fourteen multiple choice questions were designed to explore the strategies used to investigate renal effects in both ICH S7A compliant SP studies and within toxicology studies.

RESULTS

A 67% and 60% response rate was obtained in the first and second surveys, respectively. Nine out of ten respondent companies conduct renal excretory measurements (eg. urine analysis) in toxicology studies whereas only five out of ten conduct specific renal SP studies; and all of those 5 also conduct the renal excretory measurements in toxicology studies. These companies measure and/or calculate a variety of parameters as part of these studies, and also on a case by case basis include regulatory qualified and non-qualified DIKI biomarkers. Finally, only one company has used renal/urinary functional data alone to stop a project, whereas the majority of respondents combine renal data with other target organ assessments to form an integrated decision-making set.

CONCLUSION

These short surveys highlighted areas of similarity: a) urinary measurements are most commonly taken on repeat-dose toxicity studies, and b) renal SP studies are less often utilised. The two major differences are a) lack of consistent use of DIKI biomarkers in urinary safety studies and b) the way large pharmaceutical companies assess renal function. Finally, suggestions were made to improve the safety assessment methods for determining the safety of compounds with potential renal liability.

Gastrointestinal injury associated with NSAID use: a case study and review of risk factors and preventative strategies

Nonsteroidal anti-inflammatory drugs (NSAIDs) are effective anti-inflammatory and analgesic agents and are among the most commonly used classes of medications worldwide. However, their use has been associated with potentially serious dose-dependent gastrointestinal (GI) complications such as upper GI bleeding. GI complications resulting from NSAID use are among the most common drug side effects in the United States, due to the widespread use of NSAIDs. The risk of upper GI complications can occur even with short-term NSAID use, and the rate of events is linear over time with continued use. Although gastroprotective therapies are available, they are underused, and patient and physician awareness and recognition of some of the factors influencing the development of NSAID-related upper GI complications are limited. Herein, we present a case report of a patient experiencing a gastric ulcer following NSAID use and examine some of the risk factors and potential strategies for prevention of upper GI mucosal injuries and associated bleeding following NSAID use. These risk factors include advanced age, previous history of GI injury, and concurrent use of medications such as anticoagulants, aspirin, corticosteroids, and selective serotonin reuptake inhibitors. Strategies for prevention of GI injuries include anti-secretory agents, gastroprotective agents, alternative NSAID formulations, and nonpharmacologic therapies. Greater awareness of the risk factors and potential therapies for GI complications resulting from NSAID use could help improve outcomes for patients requiring NSAID treatment.

Emerging areas of research in the assessment of pharmacokinetics in patients with chronic kidney disease

Chronic kidney disease (CKD) has been shown to alter the pharmacokinetics of drugs that are eliminated not only via the renal pathway but also by nonrenal clearance and transport. Dosing recommendations in subjects with CKD have historically come from small pharmacokinetic (PK) studies, which have been insulated from the broader clinical development strategy. Opportunities for prospective strategic integration of both preclinical and clinical data on drug clearance mechanisms, model-based approaches, and clinical knowledge of therapeutic index are therefore often missed in designing and analyzing the results of PK studies in subjects with CKD, and eventually providing dosing recommendations. These considerations are valuable in designing informative PK studies in subjects with CKD, as well as for guiding kidney function-related inclusion/exclusion criteria in the broader clinical program and ultimately defining dosing guidelines that optimize benefit-risk balance for these special patient populations based on all available data. This paper offers points to consider for drug developers to increase adoption of a contemporary multidisciplinary approach, which includes key considerations on study design and conduct, methodologies for analysis (population PK and physiologically based PK modeling), and a roadmap to interpret the effect of kidney function on the overall benefit-risk profile of drugs in development.

Renal Safety Pharmacology in Drug Discovery and Development

The kidney is a complex excretory organ playing a crucial role in various physiological processes such as fluid and electrolyte balance, control of blood pressure, removal of waste products, and drug disposition. Drug-induced kidney injury (DIKI) remains a significant cause of candidate drug attrition during drug development. However, the incidence of renal toxicities in preclinical studies is low, and the mechanisms by which drugs induce kidney injury are still poorly understood. Although some in vitro investigational tools have been developed, the in vivo assessment of renal function remains the most widely used methodology to identify DIKI. Stand-alone safety pharmacology studies usually include assessment of glomerular and hemodynamic function, coupled with urine and plasma analyses. However, as renal function is not part of the ICH S7A core battery, such studies are not routinely conducted by pharmaceutical companies. The most common approach consists in integrating renal/urinary measurements in repeat-dose toxicity studies. In addition to the standard analyses and histopathological examination of kidneys, novel promising urinary biomarkers have emerged over the last decade, offering greater sensitivity and specificity than traditional renal parameters. Seven of these biomarkers have been qualified by regulatory agencies for use in rat toxicity studies.

Supervised prediction of drug-induced nephrotoxicity based on interleukin-6 and -8 expression levels

Background

Drug-induced nephrotoxicity causes acute kidney injury and chronic kidney diseases, and is a major reason for late-stage failures in the clinical trials of new drugs. Therefore, early, pre-clinical prediction of nephrotoxicity could help to prioritize drug candidates for further evaluations, and increase the success rates of clinical trials. Recently, an in vitro model for predicting renal-proximal-tubular-cell (PTC) toxicity based on the expression levels of two inflammatory markers, interleukin (IL)-6 and -8, has been described. However, this and other existing models usually use linear and manually determined thresholds to predict nephrotoxicity. Automated machine learning algorithms may improve these models, and produce more accurate and unbiased predictions.

Results

Here, we report a systematic comparison of the performances of four supervised classifiers, namely random forest, support vector machine, k-nearest-neighbor and naive Bayes classifiers, in predicting PTC toxicity based on IL-6 and -8 expression levels. Using a dataset of human primary PTCs treated with 41 well-characterized compounds that are toxic or not toxic to PTC, we found that random forest classifiers have the highest cross-validated classification performance (mean balanced accuracy = 87.8%, sensitivity = 89.4%, and specificity = 85.9%). Furthermore, we also found that IL-8 is more predictive than IL-6, but a combination of both markers gives higher classification accuracy. Finally, we also show that random forest classifiers trained automatically on the whole dataset have higher mean balanced accuracy than a previous threshold-based classifier constructed for the same dataset (99.3% vs. 80.7%).

Conclusions

Our results suggest that a random forest classifier can be used to automatically predict drug-induced PTC toxicity based on the expression levels of IL-6 and -8.

The role of drug transporters in the kidney: lessons from tenofovir

Tenofovir disoproxil fumarate, the prodrug of nucleotide reverse transcriptase inhibitor tenofovir, shows high efficacy and relatively low toxicity in HIV patients. However, long-term kidney toxicity is now acknowledged as a modest but significant risk for tenofovir-containing regimens, and continuous use of tenofovir in HIV therapy is currently under question by practitioners and researchers. Co-morbidities (hepatitis C, diabetes), low body weight, older age, concomitant administration of potentially nephrotoxic drugs, low CD4 count, and duration of therapy are all risk factors associated with tenofovir-associated tubular dysfunction. Tenofovir is predominantly eliminated via the proximal tubules of the kidney, therefore drug transporters expressed in renal proximal tubule cells are believed to influence tenofovir plasma concentration and toxicity in the kidney. We review here the current evidence that the actions, pharmacogenetics, and drug interactions of drug transporters are relevant factors for tenofovir-associated tubular dysfunction. The use of creatinine and novel biomarkers for kidney damage, and the role that drug transporters play in biomarker disposition, are discussed. The lessons learnt from investigating the role of transporters in tenofovir kidney elimination and toxicity can be utilized for future drug development and clinical management programs.

Metabolomics in nephrotoxicity

Nephrotoxicity or renal toxicity can be a result of hemodynamic changes, direct injury to cells and tissue, inflammatory tissue injury, and/or obstruction of renal excretion. Nephrotoxicity is frequently induced by a wide spectrum of therapeutic drugs and environ mental pollutants. Knowledge of the complex molecular and pathophysiologic mechanisms leading to nephrotoxicity remains limited, in part, by research that historically focused on single or relatively few risk markers. As such, current kidney injury biomarkers are inadequate in terms of sensitivity and specificity. In contrast, metabolomics enables screening of a vast array of metabolites simultaneously using NMR and MS to assess their role in nephrotoxicity development and progression. A more comprehensive understanding of these biochemical pathways would also provide valuable insight to disease mechanisms critical for drug development and treatment.

Hypertensive disorders of pregnancy and the recent increase in obstetric acute renal failure in Canada: population based retrospective cohort study

OBJECTIVE

To examine whether changes in postpartum haemorrhage, hypertensive disorders of pregnancy, or other risk factors explain the increase in obstetric acute renal failure in Canada.

DESIGN

Retrospective cohort study.

SETTING

Canada (excluding the province of Quebec).

PARTICIPANTS

All hospital deliveries from 2003 to 2010 (n=2,193,425).

MAIN OUTCOME MEASURES

Obstetric acute renal failure identified by ICD-10 diagnostic codes.

METHODS

Information on all hospital deliveries in Canada (excluding Quebec) between 2003 and 2010 (n=2,193,425) was obtained from the Canadian Institute for Health Information. Temporal trends in obstetric acute renal failure were assessed among women with and without postpartum haemorrhage, hypertensive disorders of pregnancy, or other risk factors. Logistic regression was used to determine if changes in risk factors explained the temporal increase in obstetric acute renal failure.

RESULTS

Rates of obstetric acute renal failure rose from 1.66 to 2.68 per 10,000 deliveries between 2003-04 and 2009-10 (61% increase, 95% confidence interval 24% to 110%). Adjustment for postpartum haemorrhage, hypertensive disorders, and other factors did not attenuate the increase. The temporal increase in acute renal failure was restricted to deliveries with hypertensive disorders (adjusted increase 95%, 95% confidence interval 38% to 176%), and was especially pronounced among women with gestational hypertension with significant proteinuria (adjusted increase 171%, 71% to 329%). No significant increase occurred among women without hypertensive disorders (adjusted increase 12%, -28 to 72%).

CONCLUSIONS

The increase in obstetric acute renal failure in Canada between 2003 and 2010 was restricted to women with hypertensive disorders and was especially pronounced among women with pre-eclampsia. Further study is required to determine the cause of the increase among women with pre-eclampsia.

[Turnaround time for reporting results of radiological examinations in intensive care unit patients: an internal quality control]

AIMS

The radiological examinations performed in intensive care units (ICUs) were analyzed for the purpose of internal quality control. Data included the type of examination performed, the time of day the examination was performed and the differences in radiologist report turnaround times.

MATERIAL AND METHODS

A retrospective analysis of the radiology information system (RIS) database of all radiological examinations performed in the ICU of a large German hospital from 2009 through 2011 was carried out. The search retrieved 75,169 examinations performed in ICU patients which were included in the analysis. The records were analyzed for type of radiological examination performed, i.e. conventional X-ray, ultrasound, computed tomography (CT), magnetic resonance imaging (MRI), angiography and nuclear medicine examinations, time of day the examination was performed and the interval between examination and time of reporting and release of the final report.

RESULTS

Cross-modality it took on average 52 min until a report was written and approximately 7 h before the final report was released. Turnaround times were shortest for ultrasound, conventional X-ray and CT. Over the 3-year observation period there was an overall tendency toward shorter turnaround times whereby improvement in time until reporting was most marked for conventional X-ray, MRI and ultrasound (reduction of 24, 17, and 15 min, respectively). The time until release of the final report improved most markedly for CT, conventional X-ray and angiography (improvement of approximately 6.67, 5.08 and 0.78 h, respectively).

CONCLUSIONS

During the 3-year observation period a reduction in turnaround times for reporting results and release of finalized reports could be observed, despite an increase in the total number of cases.

Tissue-engineered kidney disease models

Renal disease represents a major health problem that often results in end-stage renal failure necessitating dialysis and eventually transplantation. Historically these diseases have been studied with patient observation and screening, animal models, and two-dimensional cell culture. In this review, we focus on recent advances in tissue engineered kidney disease models that have the capacity to compensate for the limitations of traditional modalities. The cells and materials utilized to develop these models are discussed and tissue engineered models of polycystic kidney disease, drug-induced nephrotoxicity, and the glomerulus are examined in detail. The application of these models has the potential to direct future disease treatments and preclinical drug development.

Drug-induced nephrotoxicity: clinical impact and preclinical in vitro models

The kidney is a major target for drug-induced toxicity. Drug-induced nephrotoxicity remains a major problem in the clinical setting, where the use of nephrotoxic drugs is often unavoidable. This leads frequently to acute kidney injury, and current problems are discussed. One strategy to avoid such problems would be the development of drugs with decreased nephrotoxic potential. However, the prediction of nephrotoxicity during preclinical drug development is difficult and nephrotoxicity is typically detected only late. Also, the nephrotoxic potential of newly approved drugs is often underestimated. Regulatory approved or validated in vitro models for the prediction of nephrotoxicity are currently not available. Here, we will review current approaches on the development of such models. This includes a discussion of three-dimensional and microfluidic models and recently developed stem cell based approaches. Most in vitro models have been tested with a limited number of compounds and are of unclear predictivity. However, some studies have tested larger numbers of compounds and the predictivity of the respective in vitro model had been determined. The results showed that high predictivity can be obtained by using primary or stem cell derived human renal cells in combination with appropriate end points.

Acute kidney injury in solid organ transplant recipients

Delayed and slow graft function (DGF/SGF) in de novo kidney transplantation endanger outcomes of graft and patient, while predisposing the patient to acute rejection and lesser graft function. Causes and work-up of DGF/SGF are described in the present paper. Also, the epidemiology and pathophysiology of chronic renal failure both in kidney graft recipients and in recipients of other solid organs is discussed, especially in relation to calcineurin inhibitor (CNI) immunosuppression. An acute kidney injury event will have a greater and faster impact on impaired renal reserve in case of chronic renal failure. Major causes of acute kidney injury (AKI) of the native kidneys of solid organ recipients and of the transplanted kidney are: severe infections, acute toxic kidney injury caused by CNI treatment concomitant CYP450 3A4 inhibiting medication, toxic and infectious events inducing haemolytic uraemic syndrome, toxic rhabdomyolysis, acute interstitial nephritis, rapid IV immunoglobulin infusion and exposure to other well-known nephrotoxins, such as NSAIDs, amphotericin and aminoglycosides.

Solute carrier transporter and drug-related nephrotoxicity: the impact of proximal tubule cell models for preclinical research

INTRODUCTION

The final excretion step of several drugs is facilitated by membrane transporters of the Solute carrier (SLC) family expressed in the proximal tubules of the kidney. Membrane transporters contribute substantially to the pharmacokinetic profile of drugs and play important roles in drug-induced nephrotoxicity. Different cell models have been applied as tools for the assessment of nephrotoxic effects caused by drugs.

AREAS COVERED

This review gives an overview over clinically relevant SLC transporters involved in the renal elimination of drug agents and their specific role in drug-induced nephrotoxicity. Most widely applied cell models are described and their advantages and limitations are outlined.

EXPERT OPINION

In vitro cell culture models (e.g., continuous and primary renal cell lines, polarized cell monolayers) represent valuable tools for early assessment of the nephrotoxic potential of drugs. Since SLC transporters contribute to drug excretion in a large part, in vitro cell culture models might be very helpful to study transport pathways and/or potential drug-drug interactions at an early stage of the drug development process to predict nephrotoxic effects.

Protective effect of selected calcium channel blockers and prednisolone, a phospholipase-A2 inhibitor, against gentamicin and carbon tetrachloride-induced nephrotoxicity

The ameliorative effect of calcium channel blockers (CCBs) and a phospholipase-A2 inhibitor in drug-/chemical-induced nephrotoxicity was investigated. Rats were divided into 7 groups of 5 rats in each group. In the gentamicin model, group I rats were pretreated with normal saline (10 ml kg−1), while groups II–VII rats were pretreated with normal saline (10 ml kg−1), ascorbic acid (10 mg kg−1), nifedipine (0.86 mg kg−1), verapamil (4.3 mg kg−1), diltiazem (3.43 mg kg−1), and prednisolone (0.57 mg kg−1), respectively, perorally 1 h before intraperitoneal (i.p.) injection of gentamicin (40 mg kg−1) for 14 days. In the carbon tetrachloride (CCl4) model, rats were pretreated with CCBs and prednisolone for 7 days before inducing nephrotoxicity with 20% CCl4 (1.5 ml kg−1). Rats were thereafter killed and blood and tissue samples were collected for assessments. I.p. injections of gentamicin and CCl4 caused significant hypernatremia, hypokalemia, hypocalcemia, hypophosphatemia, and hyperchloremic alkalosis and reduced renal tissue levels of antioxidants. Also, significant reductions in the hemoglobin, packed cell volume, red blood cells, and platelet indices were observed. Pretreatments with nifedipine (0.86 mg kg−1), verapamil (4.3 mg kg−1), diltiazem (3.43 mg kg−1), and prednisolone (0.57 mg kg−1) significantly ameliorated the deleterious effects of gentamicin and CCl4 possibly via antioxidant and anti-lipoperoxidation mechanisms. The results obtained in this study suggest potential clinical usefulness of tested CCBs and prednisolone in drug-/chemical-induced nephrotoxicity.

Renal safety in patients treated with bisphosphonates for osteoporosis: a review

Bisphosphonates are widely used for the treatment of osteoporosis and are generally well tolerated. However, the United States Food and Drug Administration safety reports have highlighted the issue of renal safety in bisphosphonate-treated patients. All bisphosphonates carry labeled "warnings" or a contraindication for use in patients with severe renal impairment (creatinine clearance <30 or <35 mL/min). Data from pivotal trials and their extension studies of bisphosphonates approved for the management of osteoporosis were obtained via PubMed, and were reviewed with support from published articles available on PubMed. Renal safety analyses of pivotal trials of oral alendronate, risedronate, and ibandronate for postmenopausal osteoporosis showed no short-term or long-term effects on renal function. Transient postinfusion increases in serum creatinine have been reported in patients receiving intravenous ibandronate and zoledronic acid; however, studies showed that treatment with these agents did not result in long-term renal function deterioration in clinical trial patients with osteoporosis. All bisphosphonate therapies have "warnings" for use in patients with severe renal impairment. Clinical trial results have shown that even in elderly, frail, osteoporotic patients with renal impairment, intravenous bisphosphonate therapy administration in accordance with the prescribing information did not result in long-term renal function decline. Physicians should follow guidelines for bisphosphonate therapies administration at all times.

Polymethylmethacrylate dermal fillers: evaluation of the systemic toxicity in rats

This study evaluated local and systemic reactions after an intravascular injection of polymethylmethacrylate (PMMA) at two concentrations in a murine model. Thirty rats were divided equally into three groups: 2% PMMA, 30% PMMA, and a control group (normal saline only injection). The filler was injected into the ranine vein. The rats were sedated at 7 and 90 days and a clinical evaluation performed. After euthanasia, the right lung, liver, and right kidney were removed, weighed, and microscopically analyzed. The submandibular lymph nodes and tongue were removed and examined microscopically. Serum was subjected to liver and kidney function tests. No groups showed clinical alterations. Microspheres were not observed at any distant organ. Two samples from the 2% PMMA group showed a local inflammatory response at day 7 and another two samples from the 30% PMMA group at day 90. The group injected with 30% PMMA presented higher levels of alanine aminotransferase (P = 0.047) after 90 days when compared with the other groups. The data obtained in this study demonstrate that intravascular injections of PMMA fillers show potential health risks such as chronic inflammation at the implantation site.

Topographically-patterned porous membranes in a microfluidic device as an in vitro model of renal reabsorptive barriers

Models of reabsorptive barriers require both a means to provide realistic physiologic cues to and quantify transport across a layer of cells forming the barrier. Here we have topographically-patterned porous membranes with several user-defined pattern types. To demonstrate the utility of the patterned membranes, we selected one type of pattern and applied it to a membrane to serve as a cell culture support in a microfluidic model of a renal reabsorptive barrier. The topographic cues in the model resemble physiological cues found in vivo while the porous structure allows quantification of transport across the cell layer. Sub-micron surface topography generated via hot-embossing onto a track-etched polycarbonate membrane, fully replicated topographical features and preserved porous architecture. Pore size and shape were analyzed with SEM and image analysis to determine the effect of hot embossing on pore morphology. The membrane was assembled into a bilayer microfluidic device and a human kidney proximal tubule epithelial cell line (HK-2) and primary renal proximal tubule epithelial cells (RPTEC) were cultured to confluency on the membrane. Immunofluorescent staining of both cell types revealed protein expression indicative of the formation of a reabsorptive barrier responsive to mechanical stimulation: ZO-1 (tight junction), paxillin (focal adhesions) and acetylated α-tubulin (primary cilia). HK-2 and RPTEC aligned in the direction of ridge/groove topography of the membrane in the device, evidence that the device has mechanical control over cell response. This topographically-patterned porous membrane provides an in vitro platform on which to model reabsorptive barriers with meaningful applications for understanding biological transport phenomenon, underlying disease mechanisms, and drug toxicity.

Ammonium chloride enhances cisplatin cytotoxicity through DNA double-strand breaks in human cervical cancer cells

Cisplatin (cis-diamminedichloroplatinum II, CDDP) acts as a therapeutic agent by initiating cellular apoptosis. However, side-effects and drug resistance limit the clinical use of cisplatin. Numerous studies have focused on the drug-target interactions, cellular pharmacology and pharmacokinetics of cisplatin. Newly developed treatment strategies are needed in order to be used in combination with cisplatin, with the aim to minimize toxicity and to circumvent cisplatin resistance. Ammonium chloride (NH4Cl) is widely used in various areas, but its use as a combination agent with cisplatin for the treatment of cancer cells has not been previously reported. In the present study, we showed that NH4Cl could be potentially used as an effective agent in cisplatin combination treatment of HeLa human cervical cancer (HCC) cells. Cisplatin was found to inhibit cell growth, as well as to induce cell apoptosis and DNA double-strand breaks. In addition, treatment with NH4Cl increased the rate of cell apoptosis and the activation of caspase-3. Particularly, we found that NH4Cl treatment increased cisplatin‑induced phosphorylation of H2AX. In conclusion, our data indicate that NH4Cl enhances cisplatin cytotoxicity through increased DNA damage in HeLa HCC cells.

Promise of new translational safety biomarkers in drug development and challenges to regulatory qualification

One promise of new translational safety biomarkers (TSBs) is their ability to demonstrate that toxicities in animal studies are monitorable at an early stage, such that human relevance of potential adverse effects of drugs can be safely and definitively evaluated in clinical trials. Another is that they would provide an earlier, more definitive and deeper insight to patient prognosis compared with conventional biomarkers. Recent experience with regulatory authorities indicates that resource demands for new TSB qualifications under the current framework are daunting and the rate of their expansion will be slow, particularly in light of mounting financial pressures on the pharmaceutical industry. Sponsors face a dilemma over engaging in safety biomarker qualification consortia. While it is clear new TSBs could be considered catalysts to drug development and that patient health, business and scientific benefits, described here using examples, should outweigh qualification costs, concerns exist that early ambiguities in biomarker interpretations at the introduction of such new TSBs might hinder drug development.

Novel assays for detection of urinary KIM-1 in mouse models of kidney injury

Kidney injury molecule-1 (KIM-1) has been qualified by the Food and Drug Administration and European Medicines Agency as a urinary biomarker to monitor preclinical nephrotoxicity in rats and on a case-by-case basis for the translation of potentially nephrotoxic drugs into first-in human studies. Although mouse models are widely employed in preclinical studies, few urinary biomarker studies have been performed in mice due to limited urine availability and lack of sensitive assays. Here, we report the development and validation of two different assays for quantitative assessment of mouse urinary KIM-1 (uKIM-1) and compare the sensitivity of KIM-1 relative to other standard markers in ischemia reperfusion and aristolochic acid (AA)-induced kidney injury in mice. A sensitive, reproducible, and quantitative microbead-based KIM-1 ELISA was established, which requires only 10 μl urine for triplicate determination with an assay range of 12.21 pg/ml to 50 ng/ml. The second assay is a laminar flow dipstick assay, which has an assay range of 195 pg/ml to 50 ng/ml and provides quantitative assessment of KIM-1 in 15 min. uKIM-1 levels increased with increasing time of ischemia or time after AA administration. After only 10-min ischemia followed by 24-h reperfusion, uKIM-1 was significantly elevated by 13-fold, whereas serum creatinine (sCr), blood urea nitrogen, N-acetyl-β-glucosaminidase (NAG), and proteinuria levels did not change. After AA administration, uKIM-1 levels were significantly upregulated by greater than threefold within 12 h, whereas sCr and NAG levels were unchanged. Mouse KIM-1 was stable for multiple freeze-thaw cycles, for up to 5 days at room temperature and up to at least an year when stored at -80°C.

Qualified kidney biomarkers and their potential significance in drug safety evaluation and prediction

The kidney is one of the major organs drug toxicity may target. Some renal safety biomarkers have been proposed to measure kidney injury and function accordingly. Despite the widespread use for diagnosis and monitoring of renal injury and function for decades, serum creatinine and blood urea nitrogen are nonspecific biomarkers with insensitive and delayed response in the clinical setting. There is an urgent need to identify and qualify novel kidney safety biomarkers that would be used to detect and predict drug-induced nephrotoxicity in preclinical toxicological studies, clinical trials and patient care in sequence. To do that, eight novel renal safety biomarkers have been well characterized and qualified for preclinical drug safety screening, and their clinical bridging validation is underway as well. Of them, some are used to detect or predict proximal tubular injury, and others are used to diagnose and monitor glomerular damage. Thus, measurement of a panel of kidney safety biomarkers in parallel would help maximally capture all potential safety signals for a more informative decision to be made in drug research and development as well as for optimal selection of the drug and its dose in clinical practice.

Proliferative and nonproliferative lesions of the rat and mouse urinary system

The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying lesions observed in the urinary tract of rats and mice. The standardized nomenclature of urinary tract lesions presented in this document is also available electronically on the Internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous developmental and aging lesions as well as those induced by exposure to test materials. A widely accepted and utilized international harmonization of nomenclature for urinary tract lesions in laboratory animals will decrease confusion among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists.

Increased risk of chronic kidney disease among users of non-prescribed Chinese herbal medicine in Taiwan

BACKGROUND

Taiwan has the highest incidence of chronic kidney disease (CKD) and end-stage renal disease (ESRD) worldwide. Chinese herbal medicine (CHM) has been linked to CKD/ESRD in Taiwan. The specific effects and frequency of CHM on the risk of CKD are unknown.

METHODS

A hospital-based case-control study was performed from August 2006 through December 2009. The cases were consecutive nephrology outpatients 20years of age or older, with a first-time diagnosis of CKD, and without cancer or pre-existing renal disease. The controls were randomly selected outpatients that did not have CKD and were matched 1:1 to cases for age, gender and date of outpatient visit.

RESULTS

Four hundred and twenty-four patients were recruited. Among 212 cases, 23.6% took non-prescribed CHM, compared to 6.6% among the controls (p<0.001). Multivariate analysis showed that illiteracy [odds ratio (OR) 6.3, 95% confidence interval (CI) 2.4-16.6], hypertension (OR 5.4, 95% CI 2.9-9.8) and occasional use of non-prescribed CHM (OR 6.2, 95% CI 1.8-21.6) were positively associated with CKD, whereas regular exercise was inversely associated with CKD (OR 0.5, 95% CI 0.3-0.9).

CONCLUSION

Occasional use of non-prescribed CHM was associated with the risk of CKD in Taiwan.

Acute and chronic acetaminophen use and renal disease: a case-control study using pharmacy and medical claims

BACKGROUND

Studies have examined the association between acetaminophen (APAP) use and renal disease; however, their interpretation is limited by a number of methodological issues.

OBJECTIVE

To study the association between acute and chronic prescription-acquired APAP use and renal disease.

METHODS

This was a retrospective case-control study of medical and pharmacy claims of a 10% random sample of the enrollees from the IMS LifeLink Health Plans commercial claims dataset for dates of service from January 1, 1997, through December 31, 2009. Subjects were continuously enrolled and aged 18 years or older. Cases had at least 1 incident claim of renal disease defined by ICD-9-CM codes in the primary diagnosis field. Controls were randomly selected from individuals without evidence of renal disease, liver disease, or asthma in medical claims and matched to cases in a 3-to-1 ratio based on 3 variables (age, gender, and geographic region). APAP exposure, dosage, and duration of use were measured in the 7 and 30 days (acute) and in the 1-year (chronic) look-back periods. Multivariable conditional logistic regression was used to estimate the risk of APAP exposure adjusted for comorbidities, use of other nephrotoxic drugs, and health system factors.

RESULTS

There were 4,724 cases and 14,172 controls with a mean (SD) age of 60.8 (17.8) years, and 52.6% were males; 10.9% of cases and 4.2% of controls had APAP exposure in the 30 days pre-index with mean potential maximum daily dosages of 3,846.5 mg and 3,190.8 mg, respectively. Acute APAP exposure was significantly associated with renal disease, and the risk decreased with longer look-back periods (7 days: adjusted odds ratio [OR] = 1.93, 95% CI = 1.61-2.30); 30 days: OR = 1.71, 95% CI = 1.48-1.97). Cumulative APAP dosage greater than 1 kg and APAP use for longer than 30 days in the pre-index year were not significantly associated with an increased risk of renal disease (both P values = 0.900).

CONCLUSIONS

Acute prescription-acquired APAP use was associated with renal disease, while chronic use was not. Because this study assessed APAP use in pharmacy claims, further research accounting for over-the-counter APAP use is warranted before the safety of chronic APAP consumption can be firmly established.

Pathophysiology of acute kidney injury

Acute kidney injury (AKI) is the leading cause of nephrology consultation and is associated with high mortality rates. The primary causes of AKI include ischemia, hypoxia, or nephrotoxicity. An underlying feature is a rapid decline in glomerular filtration rate (GFR) usually associated with decreases in renal blood flow. Inflammation represents an important additional component of AKI leading to the extension phase of injury, which may be associated with insensitivity to vasodilator therapy. It is suggested that targeting the extension phase represents an area potential of treatment with the greatest possible impact. The underlying basis of renal injury appears to be impaired energetics of the highly metabolically active nephron segments (i.e., proximal tubules and thick ascending limb) in the renal outer medulla, which can trigger conversion from transient hypoxia to intrinsic renal failure. Injury to kidney cells can be lethal or sublethal. Sublethal injury represents an important component in AKI, as it may profoundly influence GFR and renal blood flow. The nature of the recovery response is mediated by the degree to which sublethal cells can restore normal function and promote regeneration. The successful recovery from AKI depends on the degree to which these repair processes ensue and these may be compromised in elderly or chronic kidney disease (CKD) patients. Recent data suggest that AKI represents a potential link to CKD in surviving patients. Finally, earlier diagnosis of AKI represents an important area in treating patients with AKI that has spawned increased awareness of the potential that biomarkers of AKI may play in the future.

Role of transporters in drug interactions

Over the past few decades, a tremendous amount of work has been done on the molecular characterization of transport proteins in animals and humans, leading to a better understanding of the physiological roles of a number of transport proteins. Furthermore, there is increasing preclinical and clinical evidence to support the importance of transport proteins in the pharmacokinetics and toxicokinetics of a wide variety of structurally diverse drugs. As a consequence, the degree of expression and functionality of transport proteins may directly affect the therapeutic effectiveness, safety and target specificity of drugs. Recently, there has also been increased awareness about potential drug-drug, drug-herb and drug-food interactions involving transporters. Traditionally, a change in metabolic clearance of a drug, particularly via cytochrome P450-mediated metabolism, has been considered the cause of many clinically important drug interactions. However, increasing evidence suggests that some drug interactions result from changes in the activity and/or expression of drug transporters. Accordingly, assessment of the clinical relevance of transporter-mediated drug interactions has become a regulatory issue during the drug approval process and also the evaluation of drug interaction potential has become an integral part of risk assessment during drug development processes. Therefore, this review will highlight the role of some selected drug transporters in drug interactions, as well as their clinical implication.