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Tubular secretion is a primary mechanism along with glomerular filtration for renal elimination of drugs and toxicants into urine. Organic cation transporters (OCTs) and multidrug and toxic extrusion (MATE) transporters facilitate the active secretion of cationic substrates, including drugs such as metformin and endogenous cations. We hypothesized that administration of cimetidine, an Oct/Mate inhibitor, will result in increased plasma levels and decreased renal clearance of metformin and endogenous Oct/Mate substrates in rats. A paired rat pharmacokinetic study was carried out in which metformin (5 mg/kg, intravenous) was administered as an exogenous substrate of Oct/Mate transporters to six Sprague-Dawley rats with and without cimetidine (100 mg/kg, intraperitoneal). When co-administered with cimetidine, metformin area under the curve increased significantly by 3.2-fold, and its renal clearance reduced significantly by 73%. Untargeted metabolomics was performed to investigate the effect of cimetidine on endogenous metabolome in the blood and urine samples. Over 8,000 features (metabolites) were detected in the blood, which were shortlisted using optimized criteria, i.e., a significant increase ( P value < 0.05) in metabolite peak intensity in the cimetidine-treated group, reproducible retention time, and quality of chromatogram peak. The metabolite hits were classified into three groups that can potentially distinguish inhibition of i) extra-renal uptake transport or catabolism, ii) renal Octs, and iii) renal efflux transporters or metabolite formation. The metabolomics approach identified novel putative endogenous substrates of cationic transporters that could be tested as potential biomarkers to predict Oct/Mate transporter mediated drug-drug interactions in the preclinical stages. SIGNIFICANCE STATEMENT: Endogenous substrates of renal transporters in animal models could be used as potential biomarkers to predict renal drug-drug interactions in early drug development. Here we demonstrated that cimetidine, an inhibitor of organic cation transporters (Oct/Mate), could alter the pharmacokinetics of metformin and endogenous cationic substrates in rats. Several putative endogenous metabolites of Oct/Mate transporters were identified using metabolomics approach, which could be tested as potential transporter biomarkers to predict renal drug-drug interaction of Oct/Mate substrates., (Copyright © 2024 by The American Society for Pharmacology and Experimental Therapeutics.)

Goldenseal is a perennial plant native to eastern North America. A recent clinical study reported goldenseal decreased metformin C max and area under the blood concentration versus time curve (AUC) by 27% and 23%, respectively, but half-life and renal clearance were unchanged. These observations suggested goldenseal altered processes involved in metformin absorption. The underlying mechanism(s) remain(s) unknown. One mechanism for the decreased metformin systemic exposure is inhibition by goldenseal of intestinal uptake transporters involved in metformin absorption. Goldenseal extract and three goldenseal alkaloids (berberine, (-)- β -hydrastine, hydrastinine) were tested as inhibitors of organic cation transporter (OCT) 3, plasma membrane monoamine transporter (PMAT), and thiamine transporter (THTR) 2 using human embryonic kidney 293 cells overexpressing each transporter. The goldenseal extract, normalized to berberine content, was the strongest inhibitor of each transporter (IC 50 : 4.9, 13.1, and 5.8 μ M for OCT3, PMAT, and THTR2, respectively). A pharmacokinetic study in mice compared the effects of berberine, (-)- β -hydrastine, goldenseal extract, and imatinib (OCT inhibitor) on orally administered metformin. Goldenseal extract and imatinib significantly decreased metformin C max by 31% and 25%, respectively, and had no effect on half-life. Berberine and (-)- β -hydrastine had no effect on metformin pharmacokinetics, indicating neither alkaloid alone precipitated the interaction in vivo. A follow-up murine study involving intravenous metformin and oral inhibitors examined the contributions of basolateral enteric/hepatic uptake transporters to the goldenseal-metformin interaction. Goldenseal extract and imatinib had no effect on metformin AUC and half-life, suggesting lack of inhibition of basolateral enteric/hepatic uptake transporters. Results may have implications for patients taking goldenseal with drugs that are substrates for OCT3 and THTR2. SIGNIFICANCE STATEMENT: Goldenseal is used to self-treat respiratory infections and digestive disorders. We investigated potential mechanisms for the clinical pharmacokinetic interaction observed between goldenseal and metformin, specifically inhibition by goldenseal of intestinal uptake transporters (OCT3, PMAT, THTR2) involved in metformin absorption. Goldenseal extract inhibited all three transporters in vitro and decreased metformin systemic exposure in mice. These data may have broader implications for patients co-consuming goldenseal with other drugs that are substrates for these transporters., (Copyright © 2023 by The Author(s).)

The successful prospective incorporation of in vitro transporter kinetics in physiologically based pharmacokinetic (PBPK) models to describe drug disposition remains challenging. Although determination of scaling factors to extrapolate in vitro to in vivo transporter kinetics has been facilitated by quantitative proteomics, no robust assessment comparing membrane recoveries between different cells/tissues has been made. HEK293 cells overexpressing OCT2, MATE1, and MATE2K or human kidney cortex were homogenized and centrifuged to obtain the total membrane fractions, which were subsequently subjected to liquid-liquid extraction followed by centrifugation and precipitation to isolate plasma membrane fractions. Plasma membrane recoveries determined by quantitation of the marker Na + /K + -ATPase in lysate and plasma membrane fractions were ≤20% but within 3-fold across different cells and tissues. A separate study demonstrated that recoveries are comparable between basolateral and apical membranes of renal proximal tubules, as measured by Na + /K + -ATPase and γ -glutamyl transpeptidase 1, respectively. The plasma membrane expression of OCT2, MATE1, and MATE2K was quantified and relative expression factors (REFs) were determined as the ratio between the tissue and cell concentrations. Corrections using plasma membrane recovery had minimal impact on REF values (<2-fold). In vitro transporter kinetics of metformin were extrapolated to in vivo using the corresponding REFs in a PBPK model. The simulated metformin exposures were within 2-fold of clinical exposure. These results demonstrate that transporter REFs based on plasma membrane expression enable a prediction of transporter-mediated drug disposition. Such REFs may be estimated without the correction of plasma membrane recovery when the same procedure is applied between different matrices. SIGNIFICANCE STATEMENT: Transporter REFs based on plasma membrane expression enable in vitro-in vivo extrapolation of transporter kinetics. Plasma membrane recoveries as determined by the quantification of sodium-potassium adenosine triphosphatase were comparable between the in vitro and in vivo systems used in the present study, and therefore had minimal impact on the transporter REF values., (Copyright © 2021 by The American Society for Pharmacology and Experimental Therapeutics.)

Two types of systems are used in ex vivo human placental perfusion studies to predict fetal drug exposures, that is, closed systems with recirculation of the maternal and fetal buffer and open systems using a single-pass mode without recirculation. The in vivo fetal/maternal (F:M) ratio of metformin, a cationic drug that crosses the placenta, is consistent with that reported in an open system ex vivo but not with that in a closed system. In the present study, we aimed to develop a pharmacokinetic (PK) model of transplacental transfer of metformin to predict in vivo fetal exposure to metformin and to resolve the apparent inconsistency between open and closed ex vivo systems. The developed model shows that the difference between open and closed systems is due to the difference in the time required to achieve the steady state. The model-predicted F:M ratio (approx. 0.88) is consistent with reported in vivo values [mean (95% confidence interval): 1.10 (0.69-1.51)]. The model incorporates bidirectional transport via organic cation transporter 3 (OCT3) at the basal plasma membrane, and simulations indicate that the use of trimethoprim (an OCT3 inhibitor) to prevent microbial growth in the placenta ex vivo has a negligible effect on the overall maternal-to-fetal and fetal-to-maternal clearances. The model could successfully predict in vivo fetal exposure using ex vivo human placental perfusion data from both closed and open systems. This transplacental PK modeling approach is expected to be useful for evaluating human fetal exposures to other poorly permeable compounds, besides metformin. SIGNIFICANCE STATEMENT: We developed a pharmacokinetic model of transplacental transfer of metformin, used to treat gestational diabetes mellitus, in order to predict in vivo fetal exposure and resolve the discrepancy between reported findings in open and closed ex vivo perfusion systems. The discrepancy is due to a difference in the time required to reach the steady state. The model can predict in vivo fetal exposure using data from both closed and open systems., (Copyright © 2020 The Author(s).)

The most commonly used oral antidiabetic drug, metformin, is a substrate of the hepatic uptake transporter OCT1 (gene name SLC22A1 ). However, OCT1 deficiency leads to more pronounced reductions of metformin concentrations in mouse than in human liver. Similarly, the effects of OCT1 deficiency on the pharmacokinetics of thiamine were reported to differ between human and mouse. Here, we compared the uptake characteristics of metformin and thiamine between human and mouse OCT1 using stably transfected human embryonic kidney 293 cells. The affinity for metformin was 4.9-fold lower in human than in mouse OCT1, resulting in a 6.5-fold lower intrinsic clearance. Therefore, the estimated liver-to-blood partition coefficient is only 3.34 in human compared with 14.4 in mouse and may contribute to higher intrahepatic concentrations in mice. Similarly, the affinity for thiamine was 9.5-fold lower in human than in mouse OCT1. Using human-mouse chimeric OCT1, we showed that simultaneous substitution of transmembrane helices TMH2 and TMH3 resulted in the reversal of affinity for metformin. Using homology modeling, we suggest several explanations, of which a different interaction of Leu155 (human TMH2) compared with Val156 (mouse TMH2) with residues in TMH3 had the strongest experimental support. In conclusion, the contribution of human OCT1 to the cellular uptake of thiamine and especially of metformin may be much lower than that of mouse OCT1. This may lead to an overestimation of the effects of OCT1 on hepatic concentrations in humans when using mouse as a model. In addition, comparative analyses of human and mouse orthologs may help reveal mechanisms of OCT1 transport. SIGNIFICANCE STATEMENT: OCT1 is a major hepatic uptake transporter of metformin and thiamine, but this study reports strong differences in the affinity for both compounds between human and mouse OCT1. Consequently, intrahepatic metformin concentrations could be much higher in mice than in humans, impacting metformin actions and representing a strong limitation of using rodent animal models for predictions of OCT1-related pharmacokinetics and efficacy in humans. Furthermore, OCT1 transmembrane helices TMH2 and TMH3 were identified to confer the observed species-specific differences in metformin affinity., (Copyright © 2020 by The American Society for Pharmacology and Experimental Therapeutics.)

Predicting transporter-mediated in vivo hepatic drug clearance (CL) from in vitro data (IVIVE) is important in drug development to estimate first-in-human dose and the impact of drug interactions and pharmacogenetics on hepatic drug CL. For IVIVE, one can use human hepatocytes and the traditional milligrams of protein content per gram of liver tissue (MGPGL) approach. However, this approach has been found to consistently underpredict the observed in vivo hepatic drug CL. Therefore, we hypothesized that using transporter-expressing cells and the relative expression factor (REF), determined using targeted quantitative proteomics, will accurately predict in vivo hepatic CL of drugs. We have successfully tested this hypothesis in rats with rosuvastatin, which is transported by hepatic Organic anion transporting polypeptides (OATPs). Here, we tested this hypothesis for another drug and another transporter; namely, organic cation transporter (OCT)1-mediated hepatic distributional CL of metformin. First, we estimated the in vivo metformin hepatic sinusoidal uptake CL (CL h,s,in ) of metformin by reanalysis of previously published human positron emission tomography imaging data. Next, using the REF approach, we predicted the in vivo metformin CL h,s,in using OCT1-transporter-expressing HEK293 cells or plated human hepatocytes. Finally, we compared this REF-based prediction with that using the MGPGL approach. The REF approach accurately predicted the in vivo metformin hepatic CL h,s,in , whereas the MGPGL approach considerably underpredicted the in vivo metformin CL h,s,in Based on these and previously published data, the REF approach appears to be superior to the MGPGL approach for a diverse set of drugs transported by different transporters. SIGNIFICANCE STATEMENT: This study is the first to use organic cation transporter 1-expressing cells and plated hepatocytes to compare proteomics-informed REF approach with the traditional MGPGL approach to predict hepatic uptake CL of metformin in humans. The proteomics-informed REF approach, which corrected for plasma membrane abundance, accurately predicted the positron emission tomography-imaged metformin hepatic uptake CL, whereas the MGPGL approach consistently underpredicted this CL., (Copyright © 2020 by The American Society for Pharmacology and Experimental Therapeutics.)

This study's primary objective was to fully characterize the pharmacokinetics of metformin in pregnant women with gestational diabetes mellitus (GDM) versus nonpregnant controls. Steady-state oral metformin pharmacokinetics in pregnant women with GDM receiving either metformin monotherapy ( n = 24) or a combination with glyburide ( n = 30) as well as in nonpregnant women with type 2 diabetes mellitus (T2DM) ( n = 24) were determined utilizing noncompartmental techniques. Maternal and umbilical cord blood samples were collected at delivery from 38 women. With both 500- and 1000-mg doses, metformin bioavailability, volume of distribution beta (V β ), clearance, and renal clearance were significantly increased during pregnancy. In addition, in the women receiving metformin 500 mg, significantly higher metformin apparent oral clearance (CL/F) (27%), weight-adjusted renal secretion clearance (64%), and apparent oral volume of distribution beta (V β /F) (33%) were seen during pregnancy. Creatinine clearance was significantly higher during pregnancy. Increasing metformin dose from 500 to 1000 mg orally twice daily significantly increased V β /F by 28%, weight-adjusted V β /F by 32% and CL/F by 25%, and weight-adjusted CL/F by 28% during pregnancy. Mean metformin umbilical cord arterial-to-venous plasma concentration ratio was 1.0 ± 0.1, venous umbilical cord-to-maternal concentration ratio was 1.4 ± 0.5, and arterial umbilical cord-to-maternal concentration ratio was 1.5 ± 0.5. Systemic exposure after a 500-mg dose of metformin was lower during pregnancy compared with the nonpregnant women with T2DM. However, in patients receiving metformin 1000 mg, changes in estimated bioavailability during pregnancy offset the changes in clearance leading to no significant change in CL/F with the higher dose. SIGNIFICANCE STATEMENT: Gestational diabetes mellitus complicates 5%-13% of pregnancies and is often treated with metformin. Pregnant women undergo physiological changes that alter drug disposition. Preliminary data suggest that pregnancy lowers metformin concentrations, potentially affecting efficacy and safety. This study definitively describes pregnancy's effects on metformin pharmacokinetics and expands the mechanistic understanding of pharmacokinetic changes across the dosage range. Here we report the nonlinearity of metformin pharmacokinetics and the increase in bioavailability, clearance, renal clearance, and volume of distribution during pregnancy., (U.S. Government work not protected by U.S. copyright.)

Recent pharmacogenetic evidence indicates that hepatic organic cation transporter (OCT) 1 can serve as the locus of drug-drug interactions (DDIs) with significant pharmacokinetic and pharmacodynamic consequences. We examined the impact of preincubation on the extent of OCT1 inhibition in transfected human embryonic kidney 293 (HEK293) cells. Following 30-minute preincubation with an inhibitor, approximately 50-fold higher inhibition potency was observed for cyclosporine A (CsA) against OCT1-mediated uptake of metformin compared with coincubation, with IC 50 values of 0.43 ± 0.12 and 21.6 ± 4.5 µ M, respectively. By comparison, only small shifts (≤2-fold) in preincubation IC 50 versus coincubation were observed for quinidine, pyrimethamine, ritonavir, and trimethoprim. The shift in CsA OCT1 IC 50 was substrate dependent since it ranged from >1.2- to 50.2-fold using different experimental substrates. The inhibition potential of CsA toward OCT1 was confirmed by fenoterol hepatocyte uptake experiment. Furthermore, no shift in CsA IC 50 was observed with HEK293 cells transfected with OCT2 and organic anion transporter (OAT) 1 and OAT3. Short exposure (30 minutes) to 10 µ M CsA produced long-lasting inhibition (at least 120 minutes) of the OCT1-mediated uptake of metformin in OCT1-HEK293 cells, which was likely attributable to the retention of CsA in the cells, as shown by the fact that inhibitory cellular concentrations of CsA were maintained long after the removal of the compound from the incubation buffer. The potent and persistent inhibitory effect after exposure to CsA warrants careful consideration in the design and interpretation of clinical OCT1 DDI studies. SIGNIFICANCE STATEMENT: Preincubation of OATP1B1 and OATP1B3 with their inhibitor may result in the enhancement of the inhibitory potency in a cell-based assay. However, limited data are available on potentiation of OCT1 inhibition by preincubation, which is a clinically relevant drug transporter. For the first time, we observed a 50-fold increase in CsA inhibitory potency against OCT1-mediated transport of metformin following a preincubation step. The CsA preincubation effect on OCT1 inhibition is substrate dependent. Moreover, the inhibition potential of CsA toward OCT1 is confirmed by hepatocyte uptake experiment. This study delivers clear evidences about the potent and persistent inhibitory effect on OCT1 after exposure to CsA. Further studies are needed to assess the effect of CsA on OCT1 drug substrates in vivo., (Copyright © 2019 by The American Society for Pharmacology and Experimental Therapeutics.)

Pazopanib is an orally active tyrosine kinase inhibitor that exhibits hepatotoxicity in some patients. Despite the clinical importance of its hepatic distribution, the transporter(s) responsible for hepatic uptake of pazopanib in humans remain undetermined. To characterize its hepatic uptake mechanism, we screened the effects of several transporter inhibitors, including tetrapentylammonium (TPeA) for organic cation transporters (OCTs) and cyclosporin A (CsA) for organic anion-transporting polypeptides (OATPs), on both plasma disappearance and hepatic distribution of pazopanib in mice after its i.v. administration. Among the inhibitors, TPeA largely reduced hepatic distribution and plasma clearance of pazopanib, whereas CsA showed only partial reduction. Pazopanib uptake by isolated mouse hepatocytes was similarly reduced by these inhibitors, suggesting that OCTs play a major role in the overall hepatic uptake of pazopanib in mice. In human embryonic kidney cell line HEK293 cells stably transfected with human OCT1, pazopanib uptake was significantly higher than that in vector-transfected cells. Moreover, pazopanib uptake by OCT1 became saturated and was inhibited by TPeA, but not by CsA, confirming that pazopanib is also a substrate of human OCT1. Importantly, OCT1-mediated uptake of a typical OCT1 substrate metformin was inhibited by pazopanib with an IC 50 value of 0.253 µ M, indicating that pazopanib has the potential for clinically relevant inhibition of human OCT1. Finally, pazopanib was taken up by cryopreserved human pooled hepatocytes in a time-dependent manner, and this uptake was largely reduced by TPeA but only partially reduced by CsA. Thus, the present findings suggest that OCT1 is responsible for hepatocellular uptake of pazopanib., (Copyright © 2017 by The American Society for Pharmacology and Experimental Therapeutics.)

N 1 -methylnicotinamide (1-NMN) has been investigated as an endogenous probe for the renal transporter activity of organic cation transporter 2 (OCT2) and multidrug and toxin extrusion proteins 1 and 2-K (MATE1 and MATE2-K). As pregnancy increased the renal secretion of metformin, a substrate for OCT2, MATE1, and MATE2-K, we hypothesized that the renal secretion of 1-NMN would be similarly affected. Blood and urine samples collected from women prescribed metformin for type 2 diabetes, gestational diabetes, and polycystic ovarian syndrome during early, mid, and late pregnancy ( n = 34 visits) and postpartum ( n = 14 visits) were analyzed for 1-NMN using liquid chromatography-mass spectrometry. The renal clearance and secretion clearance, using creatinine clearance to correct for glomerular filtration, were estimated for 1-NMN and correlated with metformin renal clearance. 1-NMN renal clearance was higher in both mid (504 ± 293 ml/min, P < 0.01) and late pregnancy (557 ± 305 ml/min, P < 0.01) compared with postpartum (240 ± 106 ml/min). The renal secretion of 1-NMN was 3.5-fold higher in mid pregnancy (269± 267, P < 0.05) and 4.5-fold higher in late pregnancy compared with postpartum (342 ± 283 versus 76 ± 92 ml/min, P < 0.01). Because creatinine is also a substrate of OCT2, MATE1, and MATE2-K, creatinine clearance likely overestimates filtration clearance, whereas the calculated 1-NMN secretion clearance is likely underestimated. Metformin renal clearance and 1-NMN renal clearance were positively correlated (r s = 0.68, P < 0.0001). 1-NMN renal clearance increases during pregnancy due to increased glomerular filtration and net secretion by renal transporters., (Copyright © 2017 by The American Society for Pharmacology and Experimental Therapeutics.)

The Zucker diabetic fatty (ZDF) rat, an inbred strain of obese Zucker fatty rat, develops early onset of insulin resistance and displays hyperglycemia and hyperlipidemia. The phenotypic changes resemble human type 2 diabetes associated with obesity and therefore the strain is used as a pharmacological model for type 2 diabetes. The aim of the current study was to compare the pharmacokinetics and hepatic metabolism in male ZDF and Sprague-Dawley (SD) rats of five antidiabetic drugs that are known to be cleared via various mechanisms. Among the drugs examined, metformin, cleared through renal excretion, and rosiglitazone, metabolized by hepatic cytochrome P450 2C, did not exhibit differences in the plasma clearance in ZDF and SD rats. In contrast, glibenclamide, metabolized by hepatic CYP3A, canagliflozin, metabolized mainly by UDP-glucuronosyltransferases (UGT), and troglitazone, metabolized by sulfotransferase and UGT, exhibited significantly lower plasma clearance in ZDF than in SD rats after a single intravenous administration. To elucidate the mechanisms for the difference in the drug clearance, studies were performed to characterize the activity of hepatic drug-metabolizing enzymes using liver S9 fractions from the two strains. The results revealed that the activity for CYP3A and UGT was decreased in ZDF rats using the probe substrates, and decreased unbound intrinsic clearance in vitro for glibenclamide, canagliflozin, and troglitazone was consistent with lower plasma clearance in vivo. The difference in pharmacokinetics of these two strains may complicate pharmacokinetic/pharmacodynamic correlations, given that ZDF is used as a pharmacological model, and SD rat as the pharmacokinetics and toxicology strain., (Copyright © 2016 by The American Society for Pharmacology and Experimental Therapeutics.)

As inhibitors of organic cation transporters (OCTs), proton pump inhibitors (PPIs) may affect the plasma levels of metformin, an OCT substrate. We investigated the effects of two PPIs, pantoprazole and rabeprazole, on metformin pharmacokinetics and glucose levels in healthy subjects. In this open, randomized, six-sequence, three-period crossover study, 24 participants were administered metformin, either alone or in combination with pantoprazole or rabeprazole. The plasma concentrations of metformin and serum concentrations of glucose after a 75-g oral glucose tolerance test (OGTT) were determined. The area under the concentration-time curve (AUC) for metformin was 15% and 16% greater following coadministration with pantoprazole and rabeprazole, respectively. The maximum plasma metformin concentrations (Cmax) also increased by 15% and 22%, respectively, compared with when it was administered without the PPIs. The percentage change in the AUC for glucose concentration versus time for metformin plus rabeprazole was significantly lower than that for metformin plus pantoprazole [geometric mean ratio: 0.96 (90% confidence interval: 0.92-0.99) and 0.77 (0.63-0.93), respectively]. There was no significant difference in the maximum glucose concentration. In conclusion, concomitant administration of PPIs with metformin significantly increased plasma metformin exposure, but the effects on glucose disposition were minor and varied depending on the PPI administered., (Copyright © 2014 by The American Society for Pharmacology and Experimental Therapeutics.)

Although metformin hepatic distribution is critical to pharmacological activity, the drug is cleared by urinary excretion. Metformin hepatobiliary disposition was studied in rodents representative of clinical pharmacokinetics to elucidate why metformin is not appreciably eliminated in bile. On average, 1.0% ± 0.1% of the metformin oral dose was present in the liver (liver/plasma ratio = 4.5 ± 0.6) over a pharmacologically relevant dose and time range in mice (10-300 mg/kg; 1.5-2.5 hours; T(max) = 1.4 ± 0.5; bioavailability > 59%). Distribution to the kidneys was not markedly higher, which contained 0.87% ± 0.08% of the oral dose (kidney/plasma ratio = 11.9 ± 1.1). However, only 0.11% ± 0.02% of the intravenous and bioavailable oral dose was recovered in bile, suggesting that biliary excretion is not the only route of clearance for hepatic metformin. Consistent with negligible biliary excretion, pharmacokinetics were unaffected by bile duct cannulation, proving the effective absence of enterohepatic cycling. In single-pass liver perfusion studies, 2.4% ± 0.3% of the perfused metformin dose was distributed to the liver, which underwent >300-fold greater sinusoidal than biliary excretion during the subsequent drug-free washout perfusion (74.0% ± 39.3% versus 0.222% ± 0.003% recovery of hepatic metformin in perfusate versus bile, respectively). These studies demonstrate that despite similar magnitude of metformin liver and kidney distribution, metformin biliary excretion is negligible due to predominant sinusoidal efflux from the liver.

Organic cation transporter (OCT)1 and OCT2 mediate hepatic uptake and secretory renal clearance of metformin, respectively. Pharmacokinetic/pharmacodynamic (PK/PD) implications of simultaneous impairment of both transporters, such as by systemic pan-OCT inhibition, have not been studied directly. At present metformin PK/PD, distribution, and excretion were studied in Oct1/Oct2-knockout mice. Metformin clearance was reduced 4.5-fold from renal blood flow to unbound glomerular filtration rate, and volume of distribution was reduced 3.5-fold in Oct1/Oct2-knockout mice. Oral bioavailability was not affected (F = 64 ± 4 versus 59 ± 11; knockout versus wild type). Liver- and kidney-to-plasma concentration ratios were decreased in Oct1/Oct2-knockout mice 4.2- and 2.5-fold, respectively. The 2.9-fold increase in oral metformin exposure and reduced tissue partitioning yielded little to no net change in tissue drug concentrations. Absolute kidney exposure was unchanged (knockout/wild type = 1.1 ± 0.2), and liver exposure was only modestly decreased (knockout/wild type = 0.6 ± 0.1). Oral glucose area under the curve (AUC) lowering by metformin was not impaired in Oct1/Oct2-knockout mice at the five dose levels tested (ED50 = 151 versus 110 mg/kg; glucose lowering at highest dose = 42 ± 1 versus 39 ± 4%; knockout versus wild type); however, higher systemic metformin exposures were necessary in knockout mice to elicit the same effect (half-maximal efficacious AUC = 70 versus 26 μg x h/ml). Despite major changes in metformin clearance and volume of distribution in Oct1/Oct2-knockout mice, tissue drug exposure and PD were not affected. These findings challenge the presumption that systemic OCT inhibition will affect metformin pharmacology.

Ionic liquids (ILs) are a class of salts that are expected to be used as a new source of solvents and for many other applications. Our previous studies revealed that selected ILs, structurally related organic cations, are eliminated exclusively in urine as the parent compound, partially mediated by renal transporters. This study investigated the inhibitory effects of N-butylpyridinium chloride (NBuPy-Cl) and structurally related ILs on organic cation transporters (OCTs) and multidrug and toxic extrusion transporters (MATEs) in vitro and in vivo. After Chinese hamster ovary cells expressing rat (r) OCT1, rOCT2, human (h) OCT2, hMATE1, or hMATE2-K were constructed, the ability of NBuPy-Cl, 1-methyl-3-butylimidazolium chloride (Bmim-Cl), N-butyl-N-methylpyrrolidinium chloride (BmPy-Cl), and alkyl substituted pyridinium ILs to inhibit these transporters was determined in vitro. NBuPy-Cl (0, 0.5, or 2 mg/kg per hour) was also infused into rats to assess its effect on the pharmacokinetics of metformin, a substrate of OCTs and MATEs. NBuPy-Cl, Bmim-Cl, and BmPy-Cl displayed strong inhibitory effects on these transporters (IC(50) = 0.2-8.5 μM). In addition, the inhibitory effects of alkyl-substituted pyridinium ILs on OCTs increased dramatically as the length of the alkyl chain increased. The IC(50) values were 0.1, 3.8, 14, and 671 μM (hexyl-, butyl-, and ethyl-pyridinium and pyridinium chloride) for rOCT2-mediated metformin transport. Similar structurally related inhibitory kinetics were also observed for rOCT1 and hOCT2. The in vivo coadministration study revealed that NBuPy-Cl reduced the renal clearance of metformin in rats. These results demonstrate that ILs compete with other substrates of OCTs and MATEs and could alter the in vivo pharmacokinetics of such substrates.

Our objective was to evaluate the pharmacokinetics of metformin during pregnancy. Serial blood and urine samples were collected over one steady-state dosing interval in women treated with metformin during early to late pregnancy (n = 35) and postpartum (n = 16). Maternal and umbilical cord blood samples were obtained at delivery from 12 women. Metformin concentrations were also determined in breast milk samples obtained over one dosing interval in 6 women. Metformin renal clearance increased significantly in mid (723 +/- 243 ml/min, P < 0.01) and late pregnancy (625 +/- 130 ml/min, P < 0.01) compared with postpartum (477 +/- 132 ml/min). These changes reflected significant increases in creatinine clearance (240 +/- 70 ml/min, P < 0.01 and 207 +/- 56 ml/min, P < 0.05 versus 165 +/- 44 ml/min) and in metformin net secretion clearance (480 +/- 190 ml/min, P < 0.01 and 419 +/- 78 ml/min, P < 0.01 versus 313 +/- 98 ml/min) in mid and late pregnancy versus postpartum, respectively. Metformin concentrations at the time of delivery in umbilical cord plasma ranged between nondetectable (<5 ng/ml) and 1263 ng/ml. The daily infant intake of metformin through breast milk was 0.13 to 0.28 mg, and the relative infant dose was <0.5% of the mother's weight-adjusted dose. Our results indicate that metformin pharmacokinetics are affected by pregnancy-related changes in renal filtration and net tubular transport and can be roughly estimated by the use of creatinine clearance. At the time of delivery, the fetus is exposed to metformin concentrations from negligible to as high as maternal concentrations. In contrast, infant exposure to metformin through the breast milk is low.

The purpose of the study was to elucidate mechanisms of metformin absorptive transport to explain the dose-dependent absorption observed in humans. Apical (AP) and basolateral (BL) uptake and efflux as well as AP to BL (absorptive) transport across Caco-2 cell monolayers were evaluated over a range of concentrations. Transport was concentration-dependent and consisted of saturable and nonsaturable components (K(m) approximately 0.05 mM, J(max) approximately 1.0 pmol min(-1) cm(-2), and K(d, transport) approximately 10 nl min(-1) cm(-2)). AP uptake data also revealed the presence of saturable and nonsaturable components (K(m) approximately 0.9 mM, V(max) approximately 330 pmol min(-1) mg of protein(-1), and K(d, uptake) approximately 0.04 microl min(-1) mg of protein(-1)). BL efflux was rate-limiting to transcellular transport of metformin; AP efflux was 7-fold greater than BL efflux and was not inhibited by N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide (GW918), a P-glycoprotein inhibitor. AP efflux was trans-stimulated by metformin and prototypical substrates of organic cation transporters, suggesting that a cation-specific bidirectional transport mechanism mediated the AP efflux of metformin. BL efflux of intracellular metformin was much less efficient in comparison with the overall transport, with BL efflux clearance accounting for approximately 7 and approximately 13% of the overall transport clearance at 0.05 and 10 mM metformin concentrations, respectively. Kinetic modeling of cellular accumulation and transport processes supports the finding that transport occurs almost exclusively via the paracellular route (approximately 90%) and that the paracellular transport is saturable. This report provides strong evidence for a saturable mechanism in the paracellular space and provides insight into possible mechanisms for the dose dependence of metformin absorption in vivo.

Metformin, a commonly used antidiabetic drug, exerts its glucose-lowering effect due to metabolic activities at several sites of action (biophases), including liver, intestine, muscle cells, and adipocytes. The relative contribution of the individual biophases to the overall glucose-lowering effect is not known. Thus, the aims of this investigation were to study the influence of mode of drug administration on the kinetics of glucose-lowering action of metformin in diabetic rats and identify the contribution of different sites of action to the overall response. Streptozotocin diabetic rats received metformin in crossover fashion via intraduodenal, intravenous, and intraportal routes as bolus dose or infusion regimens designed to yield similar pharmacokinetic profiles. Metformin plasma concentrations and blood glucose levels were measured following each mode of administration. Despite the similarity in the concentration-time profiles obtained for different routes of metformin administration, intraduodenal administration produced larger response than intraportal metformin infusion, and lowest response was observed following intravenous administration. This finding indicates that a significant "first-pass" pharmacodynamic effect, which occurs in the presystemic sites of action (liver and the gastrointestinal wall), contributes to the overall glucose-lowering response of metformin. We applied a combined pharmacokinetic-pharmacodynamic modeling approach to study the nature of the first-pass pharmacodynamic effect. The observed data were successfully described by a novel integrated indirect response pharmacokinetic-pharmacodynamic model that revealed a correlation between the temporal metformin concentrations that transit the portal vein and through the gut wall rather than with drug concentrations that accumulated in the liver and the intestinal wall.