Active Tubular Secretion Research Articles

A Phase I Study To Determine the Absolute Bioavailability and Absorption, Distribution, Metabolism, and Excretion of Capivasertib in Healthy Male Participants.

An open-label, single-center, phase I study was conducted to determine the absolute bioavailability and absorption, distribution, metabolism, and excretion of capivasertib-a potent, selective AKT serine/threonine kinase inhibitor-in healthy males. In part 1, six participants received a single oral dose of capivasertib (400 mg; tablets) followed by a [14C]-radiolabeled intravenous microdose of capivasertib (100 μg). After a 14-day washout, five of the participants proceeded to part 2 and received a single oral dose of [14C]capivasertib (400 mg; solution). In part 1, median time of maximum observed concentration for capivasertib was 1.7 hours, geometric mean terminal elimination half-life was 12.9 hours, and absolute bioavailability was estimated at 28.6% (90% confidence interval, 23.9 to 34.2). In part 2, a high proportion of the administered radioactivity was recovered over the 168-hour sampling period [mean recovery: 95.1% (feces, 50.4%; urine, 44.7%)]. Unchanged capivasertib in urine accounted for 7.4% of the total dose and 21.1% of the systemically available drug. Geometric mean renal clearance was 8.3 L/h, suggesting active tubular secretion. Twelve metabolites were identified in plasma. M11 (AZ14102143)-the glucuronide conjugate of capivasertib, inactive as an AKT serine/threonine kinase inhibitor-was the most abundant, accounting for a mean 78.4% of the plasma drug-related area under the curve. Of 22 metabolites identified in excreta, M11 was the most abundant (mean 28.2% of administered dose), indicating direct glucuronidation as one of the major routes of metabolism. No new safety concerns were identified. SIGNIFICANCE STATEMENT: This study provides characterization of the pharmacokinetics of capivasertib-a potent, selective AKT serine/threonine kinase (AKT) inhibitor-including absolute bioavailability, mass balance, and metabolic fate in humans; the findings are being used to inform further clinical development. Absolute bioavailability was estimated at 28.6%, and mean recovery of the administered dose in excreta over 168 hours was 95.1%. M11 (AZ14102143)-the glucuronide conjugate, inactive as an AKT inhibitor-was the most abundant identified metabolite in plasma and excreta.

Physiologically-Based Pharmacokinetic Modeling and Dosing Optimization of Cefotaxime in Preterm and Term Neonates

BackgroundCefotaxime is commonly used in treating bacterial infections in neonates. To characterize the pharmacokinetic process in neonates and evaluate different recommended dosing schedules of cefotaxime, a physiologically-based pharmacokinetic (PBPK) model of cefotaxime was established in adults and scaled to neonates. MethodsA whole-body PBPK model was built in PK-SIM® software. Three elimination pathways are composed of enzymatic metabolism in the liver, passive filtration through glomerulus, and active tubular secretion mediated by renal transporters. The ontogeny information was applied to account for age-related changes in cefotaxime pharmacokinetics. The established models were verified with realistic clinical data in adults and pediatric populations. Simulations in neonates were conducted and 100 % of the dosing interval where the unbound concentration in plasma was above the minimum inhibitory concentration (fT>MIC) was selected as the target index for dosing regimen evaluation. ResultsThe developed PBPK models successfully described the pharmacokinetic process of cefotaxime in adults and were scaled to the pediatric population. Good verification results were achieved in both adults’ and neonates’ PBPK models, indicating a good predictive performance. The optimal dosage regimen of cefotaxime was proposed according to the postnatal age (PNA) and gestational age (GA) of neonates. For preterm neonates (GA < 36 weeks), dosages of 25 mg/kg every 8 h in PNA 0–6 days and 25 mg/kg every 6 h in PNA 7–28 days were suggested. For term neonates (GA ≥ 36 weeks), dosages of 33 mg/kg every 8 h in PNA 0–6 days and 33 mg/kg every 6 h in PNA 7–28 days were recommended. ConclusionsOur study may provide useful experience in practicing PBPK model-informed precision dosing in the pediatric population.

Significance of Organic Anion Transporter 2 and Organic Cation Transporter 2 in Creatinine Clearance: Mechanistic Evaluation Using Freshly Prepared Human Primary Renal Proximal Tubule Cells.

Creatinine, a clinical marker for kidney function, is predominantly cleared by glomerular filtration, with active tubular secretion contributing to about 30% of its renal clearance. Recent studies suggested the potential involvement of organic anion transporter (OAT)2, in addition to the previously known organic cation transporter (OCT)2-mediated basolateral uptake, in creatinine active secretion. Here we characterized the transport mechanisms of creatinine using transfected human embryonic kidney (HEK)293 cells and freshly prepared human primary renal proximal tubule epithelial cells (hPTCs). Creatinine showed transport by OAT2 in transfected HEK293 cells. In addition, both creatinine and metformin showed transport by OCT2 and multidrug and toxin extrusion pump (MATE)1 and MATE2K, while penciclovir was selective for OAT2. Time-dependent cell accumulation was observed for creatinine and metformin in hPTCs. Their accumulation was increased by pyrimethamine but inhibited by decynium-22, likely due to differential inhibition of OCT2 versus MATEs. Additionally, indomethacin (an OAT2 inhibitor) reduced penciclovir uptake (∼75%) in hPTCs illustrating functional OAT2 activity. However, no modulation of creatinine and metformin cell accumulation was apparent with indomethacin. Creatinine transport characteristics in the presence of inhibitors approached those of metformin, an OCT2/MATE substrate, but were distinct from those of penciclovir, an OAT2-selective substrate. Moreover, indomethacin showed no significant effect on the basolateral-to-apical transport and net secretion of creatinine across hPTC monolayers. Collectively, the functional studies suggest OCT2 as the primary basolateral uptake mechanism and that OAT2 has a minimal role, in creatinine renal secretion. Our results highlight the utility of hPTCs to enable the functional assessment of renal transport mechanisms. SIGNIFICANCE STATEMENT: Our results obtained with primary hPTCs indicate that OCT2/MATE (vs. OAT2) play a major role in the active renal secretion of creatinine. Quantitative pharmacokinetic models should therefore focus on OCT2/MATE when describing serum creatinine and creatinine clearance modulation by inhibitor drugs and genotype- or disease-related activity changes. The present study highlights the utility of freshly isolated hPTCs to support solute carrier phenotyping to enable the functional assessment of renal transport mechanisms.

Development of a Physiologically Based Pharmacokinetic Model for Nitrofurantoin in Rabbits, Rats, and Humans.

Nitrofurantoin (NFT) is a commonly used antibiotic for the treatment of urinary tract infections that can cause liver toxicity. Despite reports of hepatic adverse events associated with NFT exposure, there is still limited understanding of the interplay between NFT exposure, its disposition, and the risk of developing liver toxicity. In this study, we aim to develop a physiologically based pharmacokinetic (PBPK) model for NFT in three different species (rabbits, rats, and humans) that can be used as a standard tool for predicting drug-induced liver injury (DILI). We created several versions of the PBPK model using previously published kinetics data from rabbits, and integrated enterohepatic recirculation (EHR) using rat data. Our model showed that active tubular secretion and reabsorption in the kidney are critical in explaining the non-linear renal clearance and urine kinetics of NFT. We subsequently extrapolated the PBPK model to humans. Adapting the physiology to humans led to predictions consistent with human kinetics data, considering a low amount of NFT to be excreted into bile. Model simulations predicted that the liver of individuals with a moderate-to-severe glomerular filtration rate (GFR) is exposed to two-to-three-fold higher concentrations of NFT than individuals with a normal GFR, which coincided with a substantial reduction in the NFT urinary concentration. In conclusion, people with renal insufficiency may be at a higher risk of developing DILI due to NFT exposure, while at the same time having a suboptimal therapeutic effect with a high risk of drug resistance. Our PBPK model can in the future be used to predict NFT kinetics in individual patients on the basis of characteristics like age and GFR.

Mass Balance and ADME Properties of Balcinrenone Following Oral Administration in Combination with Intravenous Microtracer in Healthy Subjects.

An absorption, distribution, metabolism, and excretion study was performed to determine the basic pharmacokinetic parameters, mass balance, and metabolite profiles of balcinrenone, a mineralocorticoid receptor modulator, in humans. This open-label, single-center, non-randomized study had a 2-period design. In Period 1, eight healthy male subjects were dosed with a microtracer intravenous infusion of [14C]balcinrenone shortly after receiving an oral dose of unlabeled balcinrenone in a capsule. Following a 7-day washout, the same group of subjects subsequently received an oral dose of [14C]balcinrenone as a suspension in Period 2. Clearance and absolute bioavailability of balcinrenone were determined to be 14.2 l/h and 52%, respectively. Renal clearance was determined to be 5.4 l/h (>fu • glomerular filtration rate), indicating elimination via active tubular secretion, which was potentially mediated by P-glycoprotein 1 and/or organic anion transporter 3 according to in vitro transporter data. In total, 94.1% of the oral dose was recovered; 45.2% in the urine and 48.9% in the feces. Balcinrenone was primarily metabolized via oxidation, and in vitro data suggest that cytochrome P450 3A4 was the main enzyme responsible. Intact [14C]balcinrenone accounted for 55% of drug-related material in the plasma; four metabolites were identified, each representing <6% of the total plasma radioactivity. In conclusion, this 2-period study has determined the basic pharmacokinetic parameters of balcinrenone in humans, including absolute bioavailability and disposition. No metabolites warranted further evaluation on account of their low representation, and any contribution to the pharmacodynamic response or potential drug-drug interactions was deemed negligible. Significance Statement This study provides a detailed understanding of the pharmacokinetics, disposition, and metabolism of balcinrenone following oral and microtracer intravenous administration in humans. In vitro phenotyping and transporter data granted mechanistic insights into the absorption, distribution, metabolism, and excretion properties of balcinrenone. This knowledge will guide future nonclinical and clinical studies evaluating drug-drug interactions, organ dysfunction, and safety of metabolites.

Representative Rodent Models for Renal Transporter Alterations in Human Nonalcoholic Steatohepatitis.

Alterations in renal elimination processes of glomerular filtration and active tubular secretion by renal transporters can result in adverse drug reactions. Nonalcoholic steatohepatitis (NASH) alters hepatic transporter expression and xenobiotic elimination, but until recently, renal transporter alterations in NASH were unknown. This study investigates renal transporter changes in rodent models of NASH to identify a model that recapitulates human alterations. Quantitative protein expression by surrogate peptide liquid chromatography-coupled mass spectrometry (LC-MS/MS) on renal biopsies from NASH patients was used for concordance analysis with rodent models, including methionine/choline deficient (MCD), atherogenic (Athero), or control rats and Leprdb/db MCD (db/db), C57BL/6J fast-food thioacetamide (FFDTH), American lifestyle-induced obesity syndrome (ALIOS), or control mice. Demonstrating clinical similarity to NASH patients, db/db, FFDTH, and ALIOS showed decreases in glomerular filtration rate (GFR) by 76%, 28%, and 24%. Organic anion transporter 3 (OAT3) showed an upward trend in all models except the FFDTH (from 3.20 to 2.39 pmol/mg protein), making the latter the only model to represent human OAT3 changes. OAT5, a functional ortholog of human OAT4, significantly decreased in db/db, FFDTH, and ALIOS (from 4.59 to 0.45, 1.59, and 2.83 pmol/mg protein, respectively) but significantly increased for MCD (1.67 to 4.17 pmol/mg protein), suggesting that the mouse models are comparable to human for these specific transport processes. These data suggest that variations in rodent renal transporter expression are elicited by NASH, and the concordance analysis enables appropriate model selection for future pharmacokinetic studies based on transporter specificity. These models provide a valuable resource to extrapolate the consequences of human variability in renal drug elimination. SIGNIFICANCE STATEMENT: Rodent models of nonalcoholic steatohepatitis that recapitulate human renal transporter alterations are identified for future transporter-specific pharmacokinetic studies to facilitate the prevention of adverse drug reactions due to human variability.

Abstract 5060: Tucatinib does not alter oxaliplatin PK or associated renal function: An OCT2 and MATE transport inhibition study

Abstract Background: Oxaliplatin (OX)-containing regimens are frequently utilized to treat gastrointestinal (GI) cancers. OX is eliminated predominately via urinary excretion (GFR and active tubular secretion). The contribution of active transport via OCT2 and MATE1/2-K to OX clearance is not fully understood. Tyrosine kinase inhibitors (TKIs) are frequently found to interact with OCT2/MATE transporters; however, a gap in knowledge remains between their clinical potential to impact OX pharmacokinetics (PK) and in turn, impact renal function. Tucatinib (TUC) is a highly selective human epidermal growth factor receptor 2 (HER2)-directed TKI approved in multiple regions in combination with trastuzumab and capecitabine for adult patients with metastatic HER2+ breast cancer and is currently being investigated in other HER2+ tumors. TUC inhibits OCT2/MATE-mediated transport of metformin and creatinine in vitro and in vivo. In this study, we investigated the impact of TUC on OX plasma PK, OX renal clearance (Clr), and renal function. Methods: In vitro inhibition of OCT2/MATE-mediated transport of OX by TUC was assessed in OCT2, MATE1, or MATE2-K-expressing MDCK-II cells. SGNTUC-024 (NCT04430738) is a Ph1b/2 clinical study in patients with HER2+ GI cancers evaluating the impact of TUC on the safety and PK of OX. Patients received TUC 150 mg (Cohort 1A) or 300 mg (Cohort 1B) BID starting on C1D8 of a 2-week cycle in combination with modified FOLFOX6/7. Intensive PK was collected in plasma and urine for OX alone (C1D1) or with steady-state TUC (C2D1). Total plasma platinum (Pt, analyzed as a surrogate for OX and catabolites), plasma Pt ultrafiltrate (PUF, unbound), and urine Pt were quantitatively analyzed via ICP-MS. Serum Cystatin C (CysC) was measured as a pharmacodynamic (PD) renal function marker in Cohorts 1A and 1B. Results: TUC inhibited in vitro OX transport by MATE1 (IC50 = 0.0639 µM), MATE2-K (IC50 = 0.0382 µM), and OCT2 (IC50 = 0.491 µM). In 11 patients, total Pt and PUF AUC0-8h geometric mean ratio (GMR) and 90% confidence intervals (CI) between patients who received OX alone compared to in combination were 1.1 (0.98, 1.3) and 1.0 (0.78, 1.4) in Cohort 1A (n=4) and 1.1 (0.96, 1.2) and 1.0 (0.98, 1.1) in Cohort 1B (n=7), respectively. OX GM (%CV) renal clearance (Clr,0-8h in mL/min) and fraction excreted 24h post-dose (fe,0-24h) were similar with and without TUC in both Cohort 1A (C1D1 Clr0-8h = 277 (33), fe,0-24h = 22% (17); C2D1 Clr0-8h = 249 (78), fe,0-24h = 21% (15)) and Cohort 1B (C1D1 Clr0-8h = 189 (37), fe,0-24h = 17.7% (16); C2D1 Clr0-8h = 177 (40), fe,0-24h = 16.6% (35)). Reversible slight increases in CysC (normalized to baseline) on day 3 of each cycle, irrespective of tucatinib, were observed. Conclusions: This investigation of in vitro and in vivo determinants of OX PK demonstrates that TUC does not alter the renal clearance of oxaliplatin nor renal function when OX is administered in combination with TUC. Citation Format: Ariel R. Topletz-Erickson, Anthony Lee, Vineet Kumar, Michelle Ubowski, JoAl G. Mayor, Layth I. Abdulrasool, Clark M. Henderson, Joseph A. Ware, Christopher J. Endres. Tucatinib does not alter oxaliplatin PK or associated renal function: An OCT2 and MATE transport inhibition study. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5060.

Renal clearance of graphene oxide: glomerular filtration or tubular secretion and selective kidney injury association with its lateral dimension

BackgroundRenal excretion is one of the major routes of nanomaterial elimination from the body. Many previous studies have found that graphene oxide nanosheets are excreted in bulk through the kidneys. However, how the lateral size affects GO disposition in the kidneys including glomerular filtration, active tubular secretion and tubular reabsorption is still unknown.ResultsThe thin, two-dimensional graphene oxide nanosheets (GOs) was observed to excrete in urine through the kidneys, but the lateral dimension of GOs affects their renal clearance pathway and renal injury. The s-GOs could be renal excreted via the glomerular filtration, while the l-GOs were predominately excreted via proximal tubular secretion at a much faster renal clearance rate than the s-GOs. For the tubular secretion of l-GOs, the mRNA level of basolateral organic anion transporters Oat1 and Oat2 in the kidney presented dose dependent increase, while no obvious alterations of the efflux transporters such as Mdr1 and Mrp4 mRNA expression levels were observed, suggesting the accumulation of l-GOs. During the GO renal elimination, mostly the high dose of 15 mg/kg s-GO and l-GO treatment showed obvious kidney injuries but at different renal compartment, i.e., the s-GOs induced obvious glomerular changes in podocytes, while the l-GOs induced more obvious tubular injuries including necrosis of renal tubular epithelial cells, loss of brush border, cast formation and tubular dilatation. The specifically tubular injury biomarkers KIM1 and NGAL were shown slight increase with mRNA levels in l-GO administrated mice.ConclusionsThis study shows that the lateral size of GOs affected their interactions with different renal compartments, renal excretion pathways and potential kidney injuries.

In Vitro Evaluation of P-gp-Mediated Drug-Drug Interactions Using the RPTEC/TERT1 Human Renal Cell Model.

In vitro evaluation of the P-glycoprotein (P-gp) inhibitory potential is an important issue when predicting clinically relevant drug-drug interactions (DDIs). Located within all physiological barriers, including intestine, liver, and kidneys, P-gp plays a major role in the pharmacokinetics of various therapeutic classes. However, few data are available about DDIs involving renal transporters during the active tubular secretion of drugs. In this context, the present study was designed to investigate the application of the human renal cell line RPTEC/TERT1 to study drug interactions mediated by P-gp. The P-gp inhibitory potentials of a panel of drugs were first determined by measuring the intracellular accumulation of rhodamine 123 in RPTEC/TERT1 cells. Then four drugs were selected to assess the half-maximal inhibitor concentration (IC50) values by measuring the intracellular accumulation of two P-gp-substrate drugs, apixaban and rivaroxaban. Finally, according to the FDA guidelines, the [I1]/IC50 ratio was calculated for each combination of drugs to assess the clinical relevance of the DDIs. The data showed that drugs which are known P-gp inhibitors, including cyclosporin A, ketoconazole, and verapamil, caused great increases in rhodamine 123 retention, whereas noninhibitors did not affect the intracellular accumulation of the P-gp substrate. The determined IC50 values were in accordance with the inhibition profiles observed in the rhodamine 123 accumulation assays, confirming the reliability of the RPTEC/TERT1 model. Taken together, the data demonstrate the feasibility of the application of the RPTEC/TERT1 model for evaluating the P-gp inhibitory potentials of drugs and consequently predicting renal drug interactions.

PBPK Simulation-Based Evaluation of Ganciclovir Crystalluria Risk Factors: Effect of Renal Impairment, Old Age, and Low Fluid Intake

Dosing guidance is often lacking for chronic kidney disease (CKD) due to exclusion of such patients from pivotal clinical trials. Physiologically based pharmacokinetic (PBPK) modelling supports model-informed dosing when clinical data are lacking, but application of these approaches to patients with impaired renal function is not yet at full maturity. In the current study, a ganciclovir PBPK model was developed for patients with normal renal function and extended to CKD population. CKD-related changes in tubular secretion were explored in the mechanistic kidney model and implemented either as proportional or non-proportional decline relative to GFR. Crystalluria risk was evaluated in different clinical settings (old age, severe CKD and low fluid intake) by simulating ganciclovir medullary collecting duct (MCD) concentrations. The ganciclovir PBPK model captured observed changes in systemic pharmacokinetic endpoints in mild-to-severe CKD; these trends were evident irrespective of assumed pathophysiological mechanism of altered active tubular secretion in the model. Minimal difference in simulated ganciclovir MCD concentrations was noted between young adult and geriatric populations with normal renal function and urine flow (1 mL/min), with lower concentrations predicted for severe CKD patients. High crystalluria risk was identified at reduced urine flow (0.1 mL/min) as simulated ganciclovir MCD concentrations exceeded its solubility (2.6–6 mg/mL), irrespective of underlying renal function. The analysis highlighted the importance of appropriate distribution of virtual subjects’ systems data in CKD populations. The ganciclovir PBPK model illustrates the ability of this translational tool to explore individual and combined effects of age, urine flow, and renal impairment on local drug renal exposure.Graphical

Bringing Microphysiological Systems to Practical Use: Evaluation of transporter‐mediated DDI and Renal Clearance

Active tubular secretion of drugs from the blood to urine is mediated by multiple drug transporters expressed on both basolateral and apical membrane of the proximal tubule. Human proximal tubule microphysiological system (MPS) has been proposed as a more physiologically relevant in vitro system to assess nephrotoxicity and tubular reabsorption.[1,2] However, drug-transporter studies in MPSs are currently sparse and quantitative translation of MPS data to in vivo is not yet established. This study aimed to assess the feasibility of NORTIS MPS to study quantitatively OAT1-mediated transport of pyridoxic acid (PDA) in the absence and presence of 1mM probenecid (prototypical OAT inhibitor). Conditionally immortalized proximal tubule epithelial cells overexpressing OAT1 (ciPTEC-OAT1) were seeded in the NORTIS MPS and were cultured for at least 5 days to allow cell maturation and tight tubule formation prior to transport experiments. PDA secretion rate in the apical channel effluent was linear up to 8h and plateaued between 8-24h. Inhibition of PDA secretion rate by probenecid ranged between 14 – 46% over 2-8h time period. PDA CLu,int,invitro obtained from the initial linear uptake phase was 0.07 and 0.09 µL/min/mm2 in the absence and presence of probenecid, respectively. PDA CLu,int,invitro was quantitatively scaled via total human proximal tubule surface area to CLu,int,invivo which was subsequently used to predict PDA CLR. Translation of MPS transporter data resulted in 5-fold under-prediction of PDA CLR obtained from clinical data (48.2 vs. 215 mL/min). The findings of this study demonstrate a first attempt of quantitative translation of MPS transporter data. The study also highlighted that the extent of inhibition by probenecid was not fully captured in the MPS-ciPTEC-OAT1. Further investigations of the feasibility to derive additional scaling factors for in vitro-in vivo extrapolation of transporter data from MPS are ongoing. [1] Weber, E. J., Chapron, A., Chapron, B. D., Voellinger, J. L., Lidberg, K. A., Yeung, C. K., … & Shen, D. D. (2016). Development of a microphysiological model of human kidney proximal tubule function. Kidney international, 90(3), 627-637. [2] Sakolish, C., Chen, Z., Dalaijamts, C., Mitra, K., Liu, Y., Fulton, T., … & Chiu, W. A. (2020). Predicting tubular reabsorption with a human kidney proximal tubule tissue-on-a-chip and physiologically-based modeling. Toxicology in Vitro, 63, 104752.

Influence of ABC transporters on the excretion of ciprofloxacin assessed with PET imaging in mice

Ciprofloxacin is a commonly prescribed fluoroquinolone antibiotic which is cleared by active tubular secretion and intestinal excretion. Ciprofloxacin is a known substrate of the ATP-binding cassette (ABC) transporters breast cancer resistance protein (BCRP) and multidrug resistance-associated protein 4 (MRP4). In this work, we used positron emission tomography (PET) imaging to investigate the influence of BCRP, MRP4, MRP2 and P-glycoprotein (P-gp) on the excretion of [18F]ciprofloxacin in mice. Dynamic 90-min PET scans were performed after intravenous injection of [18F]ciprofloxacin in wild-type mice without and with pre-treatment with the broad-spectrum MRP inhibitor MK571. Moreover, [18F]ciprofloxacin PET scans were performed in Abcc4(-/-), Abcc2(-/-), Abcc4(-/-)Abcg2(-/-) and Abcb1a/b(-/-)Abcg2(-/-) mice. In addition to non-compartmental pharmacokinetic (PK) analysis, a novel three-compartment PK model was developed for a detailed assessment of the renal disposition of [18F]ciprofloxacin. In MK571 pre-treated mice, a significant increase in the blood exposure to [18F]ciprofloxacin was observed along with a significant reduction in the renal and intestinal clearances. PK modelling revealed a significant reduction in renal radioactivity uptake (CL1) and in the rate constants for transfer of radioactivity from the corticomedullary renal region into blood (k2) and urine (k3), respectively, after MK571 administration. No changes in the renal clearance or in the estimated kidney PK model parameters were observed in any of the studied knockout models, while a significant reduction in the intestinal clearance was observed in Abcc2(-/-) and Abcc4(-/-)Abcg2(-/-) mice. Our data failed to reveal a role of any of the studied ABC transporters in the tubular secretion of ciprofloxacin. This may indicate that ciprofloxacin is handled in the kidneys by more than one transporter family, most likely with a great degree of mutual functional redundancy. Our study highlights the potential of PET imaging for an assessment of transporter-mediated renal excretion of radiolabelled drugs.

Is the human model RPTEC/TERT1 a relevant model for assessing renal drug efflux?

Active tubular secretion plays a major role in renal excretion of drugs thanks to the presence of many membrane transporters such as ABC transporters. These proteins facilitate drug transfer into the urine and could be a source of pharmacokinetic variabilities. Up to now, several human in vitro models of proximal tubule have been proposed but few of them have been characterized for predicting drugs renal efflux. The aim of this study was to determine whether the human model RPTEC/TERT1 meets all the criteria expected of a good model to assess renal drug transport. First, in vitro barrier properties were investigated. Then, the expression of several ABC transporters was assessed by immunofluorescence and relative quantification by liquid chromatography-high-resolution mass spectrometry (LC-HRMS) in comparison to the MDCK model. Finally, bidirectional transport studies were performed to evaluate the functionality of transporters and the abilities of model to discriminate several drugs. The RPTEC/TERT1 model formed a tight structure (192 Ω.cm2 ) that was confirmed by paracellular permeability assays. Proteomic analysis and immunofluorescence staining showed the expression of several ABC transporters. Then, only the functionality of P-gp was confirmed by the active efflux of apixaban in this study. In addition, the RPTEC/TERT1 model presents the key criteria of a renal barrier and expresses several ABC transporters. Nevertheless, the BCRP and MRP's functionality was not confirmed and further investigations are required to valid this model as in vitro model for assessing renal drug efflux.

A Physiological Approach to Pharmacokinetics in Chronic Kidney Disease.

The conventional approach to approximating the pharmacokinetics of drugs in patients with chronic kidney disease (CKD) only accounts for changes in the estimated glomerular filtration rate. However, CKD is a systemic and multifaceted disease that alters many body systems. Therefore, the objective of this exercise was to develop and evaluate a whole-body mechanistic approach to predicting pharmacokinetics in patients with CKD. Physiologically based pharmacokinetic models were developed in PK-Sim v8.0 (www.open-systems-pharmacology.org) to mechanistically represent the disposition of 7 compounds in healthy human adults. The 7 compounds selected were eliminated by glomerular filtration and active tubular secretion by the organic cation transport system to varying degrees. After a literature search, the healthy adult models were adapted to patients with CKD by numerically accounting for changes in glomerular filtration rate, kidney volume, renal perfusion, hematocrit, plasma protein concentrations, and gastrointestinal transit. Literature-informed interindividual variability was applied to the physiological parameters to facilitate a population approach. Model performance in CKD was evaluated against pharmacokinetic data from 8 clinical trials in the literature. Overall, integration of the CKD parameterization enabled exposure predictions that were within 1.5-fold error across all compounds and patients with varying stages of renal impairment. Notable improvement was observed over the conventional approach to scaling exposure, which failed in all but 1 scenario in patients with advanced CKD. Further research is required to qualify its use for first-in-CKD dose selection and clinical trial planning for a wider selection of renally eliminated compounds, including those subject to anion transport.

The Influence of Drug Properties and Ontogeny of Transporters on Pediatric Renal Clearance through Glomerular Filtration and Active Secretion: a Simulation-Based Study

Glomerular filtration (GF) and active tubular secretion (ATS) contribute to renal drug elimination, with the latter remaining understudied across the pediatric age range. Therefore, we systematically analyzed the influence of transporter ontogeny on the relative contribution of GF and ATS to renal clearance CLR for drugs with different properties in children. A physiology-based model for CLR in adults was extrapolated to the pediatric population by including maturation functions for the system-specific parameters. This model was used to predict GF and ATS for hypothetical drugs with a range of drug-specific properties, including transporter-mediated intrinsic clearance (CLint,T) values, that are substrates for renal secretion transporters with different ontogeny patterns. To assess the impact of transporter ontogeny on ATS and total CLR, a percentage prediction difference (%PD) was calculated between the predicted CLR in the presence and absence of transporter ontogeny. The contribution of ATS to CLR ranges between 41 and 90% in children depending on fraction unbound and CLint,T values. If ontogeny of renal transporters is < 0.2 of adult values, CLR predictions are unacceptable (%PD > 50%) for the majority of drugs regardless of the pediatric age. Ignoring ontogeny patterns of secretion transporters increasing with age in children younger than 2 years results in CLR predictions that are not systematically acceptable for all hypothetical drugs (%PD > 50% for some drugs). This analysis identified for what drug-specific properties and at what ages the contribution of ATS on total pediatric CLR cannot be ignored. Drugs with these properties may be sensitive in vivo probes to investigate transporter ontogeny.

Nephrotoxicity of Antimicrobials and Antibiotics.

Medication-induced nephrotoxicity remains one of the most common causes of acute kidney injury (AKI) among hospitalized patients. Within the extensive group of medications associated with AKI, antibiotics and other antimicrobials are well recognized triggers of structural and functional renal impairment. Clinical manifestations range from mild forms of tubular injury to significant deterioration of kidney function requiring acute renal replacement therapy. Several mechanisms are described, although the most frequent are acute interstitial nephritis, acute tubular necrosis, intratubular crystal deposition, and proximal/distal tubulopathy with electrolyte wasting abnormalities. General risk factors for antimicrobial-induced AKI include pre-existing chronic kidney disease, and concomitant use of medication with nephrotoxic potential. Prevention and early recognition of AKI represent the standard approach to mitigate AKI and avoid morbidity.

Predicting the pharmacokinetics of piperacillin and tazobactam in preterm and term neonates using physiologically based pharmacokinetic modeling

A probabilistic-based seven-compartment fit for purpose PBPK model for the preterm and term neonates was constructed and used with the combination antimicrobial drugs piperacillin (PIP) and tazobactam (TAZ) as a case study. Anthropomorphic maturation equations with distributions were used to account for variability in growth patterns for neonates born premature (gestation age ≥ 25 weeks). Renal excretion, the primary pathway for elimination of these drugs from the body, was described by passive diffusion (glomerular filtration, GFR) and active tubular secretion. Tubular secretion rates were calculated using in-vitro to in-vivo extrapolation methods for OAT1 and OAT3 protein transporters. Competitive inhibition of each anion (PIP and TAZ) for tubular secretion by the OAT transporters suggested that PIP decreased the systemic clearance rate of TAZ. After accounting for variability in maturation of growth (organs, kidney function and blood flows) model predictions did not account for all the observed variability in the pharmacokinetic plasma data for PIP and TAZ. For the 31 preterm and term neonates, the PBPK model for PIP and TAZ, with no adjustments in model parameters, was judged successful for 48% and 43% of the preterm neonates and 25% of the term neonates. Further refinements in model parameters to increase model performance include experiments to determine plasma protein binding in preterm and term neonates and solubility or partitioning of PIP and TAZ into tissues. A better understanding of the role of illness on modifying pharmacokinetic behavior of PIP and TAZ is needed.

Involvement of Renal Efflux Transporter MATE1 in Renal Excretion of Flecainide.

Flecainide, an anti-arrhythmic drug, undergoes renal excretion through active renal tubular secretion in addition to passive glomerular filtration. The contribution of renal uptake and efflux transporters in active renal tubular secretion of flecainide remains unclear except that flecainide is a substrate of human multidrug resistance protein 1 (MDR1). To elucidate renal efflux and uptake transporters involved with active renal tubular secretion of flecainide, we conducted in vitro interaction studies of flecainide using organic cation transporter 2 (OCT2), multidrug and toxin extrusion (MATE) 1, and MATE2-K. Uptake transporter inhibition assays using hOCT2-Chinese hamster ovary (CHO), hMATE1-CHO, and hMATE2-K-Madin Darby canine kidney strain II (MDCKII) cells revealed that flecainide (2.5 µM) inhibited hMATE1-mediated transport by 40% with an IC50 value of 6.7 µM; however, it showed no or weak inhibitory effects on hOCT2- and hMATE2-K-mediated transport. For investigating flecainide as a substrate of hMATE1, the accumulation of flecainide in hMATE1-CHO was compared with that in control cells. Uptake transporter substrate assay revealed that flecainide (1 µM) showed 1.11-fold accumulation though the hMATE1-related active transport was significantly decreased in the presence of quinidine (42.0 ± 23.9 vs. 11.8 ± 4.1 pmol/mg in transfected cells; p < 0.05). These results suggest that flecainide is a weak substrate of hMATE1, which is involved in the renal tubular secretion of cationic drugs, and hMATE1 may be less important in the pharmacokinetic drug-drug interaction for renal excretion of flecainide. However, in vivo drug-drug interaction studies of flecainide with substrates of hMATE1 may be needed because flecainide has the potential to inhibit hMATE1.

An Overview of Factors Affecting Renal Clearance

Biological Renal clearance comprises multiple active and passive mechanisms, in turn leading to the formation of urine. In this article, a brief review of passive filtration in glomerular capillaries, active tubular secretion, and reabsorption is discussed. Factors affecting renal clearance have also been brought into the discussion, encompassing drug physicochemical properties, drug concentration, the volume of distribution, protein binding, blood flow to kidneys, biological factors, and drug interactions. Further, the necessity of dose adjustment in patients suffering renal impairment has been highlighted.

Fabrication of Kidney Proximal Tubule Grafts Using Biofunctionalized Electrospun Polymer Scaffolds.

The increasing prevalence of end-stage renal disease and persistent shortage of donor organs call for alternative therapies for kidney patients. Dialysis remains an inferior treatment as clearance of large and protein-bound waste products depends on active tubular secretion. Biofabricated tissues could make a valuable contribution, but kidneys are highly intricate and multifunctional organs. Depending on the therapeutic objective, suitable cell sources and scaffolds must be selected. This study provides a proof-of-concept for stand-alone kidney tubule grafts with suitable mechanical properties for future implantation purposes. Porous tubular nanofiber scaffolds are fabricated by electrospinning 12%, 16%, and 20% poly-ε-caprolactone (PCL) v/w (chloroform and dimethylformamide, 1:3) around 0.7 mm needle templates. The resulting scaffolds consist of 92%, 69%, and 54% nanofibers compared to microfibers, respectively. After biofunctionalization with L-3,4-dihydroxyphenylalanine and collagen IV, 10×106 proximal tubule cells per mL are injected and cultured until experimental readout. A human-derived cell model can bridge all fiber-to-fiber distances to form a monolayer, whereas small-sized murine cells form monolayers on dense nanofiber meshes only. Fabricated constructs remain viable for at least 3 weeks and maintain functionality as shown by inhibitor-sensitive transport activity, which suggests clearance capacity for both negatively and positively charged solutes.