Interaction between methotrexate and nonsteroidal anti-inflammatory drugs in organic anion transporter

Targeting Glial Cells by Organic Anion-Transporting Polypeptide 1C1 (OATP1C1)-Utilizing l-Thyroxine-Derived Prodrugs

OATP1C1 (organic anion-transporting polypeptide 1C1) transports thyroid hormones, particularly thyroxine (T4), into human astrocytes. In this study, we investigated the potential of utilizing OATP1C1 to improve the delivery of anti-inflammatory drugs into glial cells. We designed and synthesized eight novel prodrugs by incorporating T4 and 3,5-diiodo-l-tyrosine (DIT) as promoieties to selected anti-inflammatory drugs. The prodrug uptake in OATP1C1-expressing human U-87MG glioma cells demonstrated higher accumulation with T4 promoiety compared to those with DIT promoiety or the parent drugs themselves. In silico models of OATP1C1 suggested dynamic binding for the prodrugs, wherein the pose changed from vertical to horizontal. The predicted binding energies correlated with the transport profiles, with T4 derivatives exhibiting higher binding energies when compared to prodrugs with a DIT promoiety. Interestingly, the prodrugs also showed utilization of oatp1a4/1a5/1a6 in mouse primary astrocytes, which was further supported by docking studies and a great potential for improved brain drug delivery.

Recent Advances in Synthetic Drugs and Natural Actives Interacting with OAT3

Organic anion transporter 3 (OAT3) is predominantly expressed in the kidney and plays a vital role in drug clearance. Consequently, co-ingestion of two OAT3 substrates may alter the pharmacokinetics of the substrate. This review summarizes drug-drug interactions (DDIs) and herbal-drug interactions (HDIs) mediated by OAT3, and inhibitors of OAT3 in natural active compounds in the past decade. This provides a valuable reference for the combined use of substrate drugs/herbs for OAT3 in clinical practice in the future and for the screening of OAT3 inhibitors to avoid harmful interactions.

A critical review of methotrexate clinical interactions: role of transporters

INTRODUCTION

Methotrexate (MTX) is an anti-folate and immunosuppressive drug prescribed for various malignancies and immune diseases. However, delayed elimination of MTX associated with concomitant use of some medications can lead to severe and life-threatening adverse effects.

AREAS COVERED

This paper investigated drug-MTX interactions that lead to elevated MTX levels and related adverse effects due to the role of transporters. Methotrexate toxicity occurs at both low and high doses administrations. According to the studies we reviewed in this paper, most interaction records with methotrexate occurred with co-administration of indomethacin, ketoprofen, omeprazole, piperacillin/tazobactam, ciprofloxacin, co-trimoxazole, probenecid, and imatinib, mainly due to the role of transporters. However, most studies were performed as case reports or series, and confirming the exact drug-methotrexate interaction still needs further clinical investigations.

EXPERT OPINION

Our findings showed no firm evidence of interactions of proton pump inhibitors (PPIs), levetiracetam, and NSAIDS with MTX. Moreover, patients' risk factors, hypoalbuminemia, renal failure, third space fluid retention, the elderly, polypharmacy, and transport inhibition are the most critical factors for MTX toxicity. If substitution or temporary discontinuation is not possible, healthcare providers should be aware of interactions, especially in patients with risk factors for MTX toxicity.

Efficacy of vitamin E in protection against methotrexate induced placental injury in albino rats

Methotrexate (MXT) is a chemotherapeutic drug that has been used in a wide range of clinical practices. Unfortunately, the administration of MXT during pregnancy may induce abortion, fetal deformities, and intrauterine growth retardation. Vitamin E is an antioxidant agent that can ameliorate free radical damage. The current work aimed to shed more light on the possible protective effect of vitamin E against MXT induced placental toxicity and to determine the possible mechanisms; biochemically, histologically, and immunohistochemically. Four groups were used: control pregnant, Vitamin E (VIT E) pregnant, Methotrexate (MXT) pregnant, and Vitamin E Methotrexate (VIT E-MXT) pregnant. The placental tissues were processed for light, immunohistochemical, and electron microscopic study. Other samples were obtained for biochemical study; the placental oxidant/antioxidant status was evaluated. The results showed that MXT caused various placental morphological changes in the form of distorted chorionic projection with an accumulation of hemosiderin granules in the trophoblastic cells. Maternal blood vessels showed a homogenous acidophilic material Edema of the extra-embryonic fetal membranes was noticed. A significant decreased in placental weight as well as increase in the oxidative and inflammatory markers were detected. Increased COX2 and decreased eNOS expressions were observed in the MXT group if compared to the control group. VIT E significantly restored the normal histological and immunohistochemical appearance, placental weight, and oxidant/antioxidant balance. It could be concluded the biochemical, morphological, and morphometric findings suggested that vitamin E coadministration is promising in attenuating the placental toxic effect of methotrexate. In this study, VIT E decreased the inflammatory and oxidative stress effect of methotrexate on the placental tissue by enhancing the level of eNOS.

Enantioselective Drug Recognition by Drug Transporters

Drug transporters mediate the absorption, tissue distribution, and excretion of drugs. The cDNAs of P-glycoprotein, multidrug resistance proteins (MRPs/ABCC), breast cancer resistance protein (BCRP/ABCG2), peptide transporters (PEPTs/SLC15), proton-coupled folate transporters (PCFT/SLC46A1), organic anion transporting polypeptides (OATPs/SLCO), organic anion transporters (OATs/SLC22), organic cation transporters (OCTs/SLC22), and multidrug and toxin extrusions (MATEs/SLC47) have been isolated, and their functions have been elucidated. Enantioselectivity has been demonstrated in the pharmacokinetics and efficacy of drugs, and is important for elucidating the relationship with recognition of drugs by drug transporters from a chiral aspect. Enantioselectivity in the transport of drugs by drug transporters and the inhibitory effects of drugs on drug transporters has been summarized in this review.

Identification of drug transporters involved in the uptake and efflux of rhein in hepatocytes

Rhein is an herbal medicine with various bioactivities and is derived from an anthraquinone compound. In this study, we aimed to identify drug transporters involved in the uptake and efflux of rhein in hepatocytes.

Renal Drug Transport and Drug-Drug Interactions

The kidney plays a vital role in the elimination of xenobiotics including drugs, toxins, and endogenous metabolites. Renal drug elimination involves 3 major processes: glomerular filtration, tubular secretion, and tubular reabsorption. Although glomerular filtration is a simple unidirectional diffusion process, renal tubular secretion and/or reabsorption can involve saturable processes mediated by multiple highly specialized membrane transport systems. Current research has identified that these transport proteins play a significant role in the efficient removal and/or reabsorption of pharmacological agents. Since the majority of membrane transporters have broad substrate specificity, there is a significant risk for drug-drug interactions through competition for similar transport pathways. This article will focus on the cellular expression, localization, and transport properties of various renal drug transport systems (ie, organic anion, organic cation, nucleoside, and adenosine triphosphate [ATP]-dependent efflux transporters). Specific examples of drugs that are transported by each of these mechanisms will be provided. Clinically relevant drug-drug interactions involving renal drug transporters will be discussed to guide the clinician in understanding and preventing these interactions.

Evaluation of drug-drug interaction between the novel cPLA2 inhibitor AK106-001616 and methotrexate in rheumatoid arthritis patients

1. Drug interaction potential between AK106-001616, a novel cytosolic phospholipase A2 inhibitor, and methotrexate (MTX) in rheumatoid arthritis patients was investigated. This trial is registered with ClinicalTrials.gov, number NCT00902369. 2. In the clinical study, the 90% confidence intervals (CIs) for the geometric mean ratio (GMR) of AUC0-t of MTX administered after AK106-001616 200 mg compared to the MTX without AK106-001616 were within 80-125%. However, administration of AK106-001616 at doses of 400 and 600 mg exceeded the 125% threshold. As small but statistically significant increases in AUC0-t were observed, we investigated the mechanism for this drug-drug interaction between MTX and AK106-001616. 3. In vitro, AK106-001616 inhibited OAT1 (IC50 = 18.4 μM, Ki = 33.6 μM) in a non-competitive manner and OAT3 (IC50 = 1.80 μM, Ki = 1.49 μM) in a competitive manner. Both transporters are involved in MTX transport in renal proximal tubules. 4. AK106-001616 has a weak drug interaction with MTX. In vitro studies provide a mechanistic understanding of the in vivo inhibition of transporters by AK106-001616.

How drugs get into cells: tested and testable predictions to help discriminate between transporter-mediated uptake and lipoidal bilayer diffusion

One approach to experimental science involves creating hypotheses, then testing them by varying one or more independent variables, and assessing the effects of this variation on the processes of interest. We use this strategy to compare the intellectual status and available evidence for two models or views of mechanisms of transmembrane drug transport into intact biological cells. One (BDII) asserts that lipoidal phospholipid Bilayer Diffusion Is Important, while a second (PBIN) proposes that in normal intact cells Phospholipid Bilayer diffusion Is Negligible (i.e., may be neglected quantitatively), because evolution selected against it, and with transmembrane drug transport being effected by genetically encoded proteinaceous carriers or pores, whose “natural” biological roles, and substrates are based in intermediary metabolism. Despite a recent review elsewhere, we can find no evidence able to support BDII as we can find no experiments in intact cells in which phospholipid bilayer diffusion was either varied independently or measured directly (although there are many papers where it was inferred by seeing a covariation of other dependent variables). By contrast, we find an abundance of evidence showing cases in which changes in the activities of named and genetically identified transporters led to measurable changes in the rate or extent of drug uptake. PBIN also has considerable predictive power, and accounts readily for the large differences in drug uptake between tissues, cells and species, in accounting for the metabolite-likeness of marketed drugs, in pharmacogenomics, and in providing a straightforward explanation for the late-stage appearance of toxicity and of lack of efficacy during drug discovery programmes despite macroscopically adequate pharmacokinetics. Consequently, the view that Phospholipid Bilayer diffusion Is Negligible (PBIN) provides a starting hypothesis for assessing cellular drug uptake that is much better supported by the available evidence, and is both more productive and more predictive.

Effects of 1α,25-dihydroxyvitamin D3 , the natural vitamin D receptor ligand, on the pharmacokinetics of cefdinir and cefadroxil, organic anion transporter substrates, in rat

Evidence in the literature suggests that 1α,25-dihydroxyvitamin D3 [1,25(OH)2 D3 ], the vitamin D receptor ligand, down-regulated the expression of the rat renal organic anion (renal organic anion transporter, rOAT) and oligopeptide (rPEPT) transporters, but increased intestinal rPEPT1 expression. We investigated, in rats, the intravenous and oral pharmacokinetics of 2 mg/kg cefdinir and cefadroxil, two cephalosporins that are eliminated via renal OAT1/OAT3 and are substrates of PEPT1/PEPT2, with and without 1,25(OH)2 D3 treatment. The area under the plasma concentration-time curve (AUC) of cefdinir or cefadroxil after 1,25(OH)2 D3 treatment was increased significantly because of decreased clearance (CL). Both kidney uptake and cumulative urinary recovery were significantly decreased, whereas liver uptake and fecal recovery remained unchanged in 1,25(OH)2 D3 -treated rats. Similar changes in AUC and CL were observed for both drugs upon coadministration of probenecid, the OAT inhibitor. Oral availability of cefdinir and cefadroxil remained unchanged with 1,25(OH)2 D3 treatment, suggesting lack of a role for intestinal rPEPT1. Rather, reduction of rOAT1/rOAT3 mRNA expression in kidney with 1,25(OH)2 D3 -treatment was observed, confirmed by decreased function in MDCKII cells overexpressing human OAT1 and OAT3. These composite results suggest that 1,25(OH)2 D3 treatment reduces cefdinir and cefadroxil clearances by diminution of renal OAT1/OAT3 expression, implicating a role for 1,25(OH)2 D3 in eliciting transporter-based drug interactions.

Rationale for further medical and health research on high-potency sweeteners

High-potency or artificial sweeteners have historically been considered inert compounds without physiological consequences other than taste sensations. However, recent data suggest that some of these sweeteners have biological effects that may impact human health. Furthermore, there are significant gaps in our current knowledge of the pharmacokinetics of these sweeteners, their potential for "sweetener-drug interactions" and their impact on appetite and body weight regulation. Nine research needs are described that address some of the major unknown issues associated with ingestion of high-potency sweeteners.

Peptide cotransporter 1 in intestine and organic anion transporters in kidney are targets of interaction between JBP485 and lisinopril in rats

The purpose of this study was to clarify the pharmacokinetic mechanism of interaction between JBP485 (cyclo-trans-4-L-hydroxyprolyl-L-serine, a dipeptide with antihepatitis activity) and lisinopril (an angiotensin-converting enzyme inhibitor) in vitro and in vivo. When JBP485 and lisinopril were administered orally simultaneously, the plasma concentrations of the two drugs were decreased significantly, but few changes were observed after simultaneous intravenous administration of the two drugs. The uptake of JBP485 and lisinopril in everted intestinal sacs and in HeLa cells transfected with human peptide cotransporter 1 (PEPT1), as well as absorption of JBP485 and lisinopril after jejunal perfusion were reduced after simultaneous drug administration, which suggested that the first target of drug interaction was PEPT1 in the intestine during the absorption process. The cumulative urinary excretions and renal clearance of the two drugs were decreased after intravenous co-administration, while uptakes of the two drugs in kidney slices and hOAT1/hOAT3-transfected HEK293 cells were decreased. These results indicated that the second target of drug-drug interaction was located in the kidney. These findings confirmed that the pharmacokinetic mechanism of interaction between JBP485 and lisinopril could be explained by their inhibition of the same transporters in the intestinal mucosa (PEPT1) and kidneys (OATs).

In vitro and in vivo evidence of the importance of organic anion transporters (OATs) in drug therapy

Organic anion transporters 1-10 (OAT1-10) and the urate transporter 1 (URAT1) belong to the SLC22A gene family and accept a huge variety of chemically unrelated endogenous and exogenous organic anions including many frequently described drugs. OAT1 and OAT3 are located in the basolateral membrane of renal proximal tubule cells and are responsible for drug uptake from the blood into the cells. OAT4 in the apical membrane of human proximal tubule cells is related to drug exit into the lumen and to uptake of estrone sulfate and urate from the lumen into the cell. URAT1 is the major urate-absorbing transporter in the apical membrane and is a target for uricosuric drugs. OAT10, also located in the luminal membrane, transports nicotinate with high affinity and interacts with drugs. Major extrarenal locations of OATs include the blood-brain barrier for OAT3, the placenta for OAT4, the nasal epithelium for OAT6, and the liver for OAT2 and OAT7. For all transporters we provide information on cloning, tissue distribution, factors influencing OAT abundance, interaction with endogenous compounds and different drug classes, drug/drug interactions and, if known, single nucleotide polymorphisms.

Drug interaction between celecoxib and methotrexate in organic anion transporter 3-transfected renal cells and in rats in vivo

Methotrexate has a clinically important pharmacokinetic interaction with nonsteroidal anti-inflammatory drugs (NSAIDs) mainly through its competition for tubular secretion via the renal organic anion transporter 3 (OAT3). We have previously reported the usefulness of OAT3-transfected renal tubular cells for screening of the drugs which interfere with the pharmacokinetics of methotrexate. Celecoxib, a cyclooxygenase (COX) 2 inhibitor, has not been reported to interact with methotrexate, but the mechanisms are unclear why the interaction did not occur. The purpose of this study was to evaluate the effect of celecoxib on methotrexate tubular secretion using a renal cell line stably expressing human OAT3 (S2-hOAT3), and to evaluate the pharmacokinetic interaction of the two drugs in rats. [3H]methotrexate uptake into S2-hOAT3 cells was significantly inhibited by celecoxib in a concentration-dependent manner and the Ki value was 35.3 microM. However, methotrexate serum concentrations and urinary excretion of methotrexate over 24 h in rats were not affected by celecoxib (50, 200 mg/kg). Celecoxib serum concentrations were increased by the increase in celecoxib dosage and the maximum drug concentration (Cmax) was 20.6 microM (celecoxib 200 mg/kg), which did not reach the Ki value obtained in the in vitro study. These results indicated that celecoxib inhibited the secretion of methotrexate via hOAT3, which suggested that celecoxib was a substrate of hOAT3. However, co-administration of the two drugs at clinical dosage did not affect the pharmacokinetics of methotrexate, because the serum concentrations did not reach the Ki value. Although the accumulation study using S2-hOAT3 cells was useful to predict the interaction between the new drug and methotrexate in vivo, a comparison of the Ki value with the Cmax in clinical dosage was necessary to evaluate the degree of this interaction.

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

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

Effect of ketoprofen and its enantiomers on the renal disposition of methotrexate in the isolated perfused rat kidney

Non-steroidal anti-inflammatory drugs (NSAIDs) have been shown to inhibit the renal tubular secretion of methotrexate. However, the relative contribution of the active S- and inactive R-enantiomers is unknown. This study examined the effect of racemic ketoprofen and its enantiomers on the renal disposition of methotrexate in the isolated perfused rat kidney (IPK). Nineteen kidneys were divided between a control and three treatment groups. Controls were perfused with methotrexate alone (25 μg mL−1, n = 5) over three 30-min periods. Treatment groups were perfused with methotrexate (25 μg mL−1) for the first period, followed by a second period of methotrexate (25 μg mL−1) plus R- (n = 5), S- (n = 5) or RS-ketoprofen (n = 4) at 25 μg mL−1, and a third period of methotrexate (25 μg mL−1) plus R-, S- or RS-ketoprofen (50 μg mL−1). Perfusate and urine were collected over 10-min intervals. Methotrexate was measured by HPLC and its binding in perfusate by ultrafiltration. The clearance ratio (CR) for methotrexate was obtained by dividing the renal clearance by the product of its fraction unbound and the glomerular filtration rate. During control experiments, there was no significant change in the CR over 90 min. R-, S- and RS-ketoprofen at 50 μg mL−1 reduced the CR of methotrexate significantly, but there was no difference between the three groups. While the enantiomers of ketoprofen reduced the renal excretion of methotrexate, the interaction was not enantioselective.

Intervention of alpha-lipoic acid ameliorates methotrexate-induced oxidative stress and genotoxicity: A study in rat intestine

Methotrexate (MTX) is an anti-metabolite, widely used in the cancer chemotherapy and rheumatoid arthritis. However, its long-term clinical use is restricted on account of its severe intestinal toxicity. The present study was aimed to investigate the intestinal toxicity of MTX and the possible protective effect of alpha-lipoic acid (LA) on Sprague-Dawley rats. MTX-induced intestinal toxicity was evaluated at the dose of 2.5mg/kg for short-term (5 days treatment) and 1mg/kg for long-term (5 days in a week for four consecutive weeks treatment) study. The possible protective effect of LA was evaluated in both short- as well as long-term study in a dose-dependent manner. MTX treatment induced diarrhoea and mortality in rats, indicating its severe toxicity in the target organ of investigation, i.e., intestine. Further, the intestinal toxicity of MTX was assessed by evaluating different parameters of oxidative stress, DNA damage, cytotoxicity as well as histological changes. Immunostaining for p53 revealed higher genotoxic assault in the intestinal cells due to MTX treatment. Pretreatment of rats with LA led to significant decrease in the oxidative stress, DNA damage, cellular damage, inflammatory changes and apoptosis as determined by malondialdehyde level, glutathione level, comet assay parameters, histological evaluation, immunostaining and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay. In the present investigation, we report that LA pretreatment ameliorates MTX-induced intestinal toxicity in rat as evident from the protection against oxidative stress, decrease in DNA damage and protection of cellular morphology as well as improvement in the stool consistency and animal survival rate.

Altered intravenous pharmacokinetics of topotecan in rats with acute renal failure (ARF) induced by uranyl nitrate: Do adenosine A1antagonists (selective/non-selective) normalize the altered topotecan kinetics in ARF?

A series of exploratory investigations with multiple agents was carried out in normal rats and in rats with uranyl nitrate-induced acute renal failure to understand the disposition characteristics of intravenous topotecan (TPT) used as a model substrate. The disposition of TPT was unaltered in normal rats when treated with methotrexate, whereas treatment with probenecid increased the systemic exposure of TPT. In case of uranyl nitrate-induced acute renal failure (UN-ARF) rats, the systemic exposure of TPT was increased when compared with normal rats, whereas in UN-ARF rats treated with probenecid a further reduction in renal clearance of TPT was noted as compared with that of UN-ARF induced rats. Thus, TPT may be involved in the tubular secretory pathway when a passive glomerular filtration pathway for elimination was not possible. The disposition of TPT did not normalize in UN-ARF rats when treated with caffeine, a non-selective adenosine A1 receptor antagonist, whereas the selective adenosine A1 receptor antagonist (1,3-dipropyl-8-phenylxanthine, DPPX) normalized TPT pharmacokinetic disposition by improving renal function. Renal excretion studies demonstrated that CLR improved by almost fivefold following DPPX treatment in ARF rats. In addition, the qualitative stability/metabolism pattern of TPT in liver microsomes prepared from various groups of rats (normal rats, UN-ARF rats, rats treated with DPPX, and UN-ARF rats treated with DPPX) was found to be similar. In summary, using a pharmacokinetic tool as a surrogate, it has been shown that the pharmacokinetic disposition of TPT improved considerably upon treatment with DPPX, a selective adenosine A1 antagonist.

Inhibition of human organic anion transporter 3 mediated pravastatin transport by gemfibrozil and the metabolites in humans

Coadministration of gemfibrozil (600 mg, b.i.d., 3 days) with pravastatin (40 mg/day) decreased the renal clearance of pravastatin by approximately 40% in healthy volunteers. To investigate the mechanism of this drug-drug interaction in the renal excretion process, we undertook an uptake study of pravastatin using human organic anion transporters (hOATs)-expressing S2 cells. hOAT3 and hOAT4 transported pravastatin in a saturatable manner with Michaelis--Menten constants of 27.7 microM and 257 microM respectively. On the other hand, hOAT1 and hOAT2 did not transport pravastatin. Gemfibrozil and its glucuronide and carboxylic metabolite forms inhibited the uptake of pravastatin by hOAT3 with IC(50) values of 6.8 microM, 19.7 microM and 5.4 microM, respectively. Considering the plasma concentrations of gemfibrozil and its metabolites in humans, the inhibition of hOAT3-mediated pravastatin transport by gemfibrozil and its metabolites would lead to a decrease in the renal clearance of pravastatin in clinical settings.

Pharmacogenetics of analgesics: toward the individualization of prescription

The use of analgesics is based on the empiric administration of a given drug with clinical monitoring for efficacy and toxicity. However, individual responses to drugs are influenced by a combination of pharmacokinetic and pharmacodynamic factors that can sometimes be regulated by genetic factors. Whereas polymorphic drug-metabolizing enzymes and drug transporters may affect the pharmacokinetics of drugs, polymorphic drug targets and disease-related pathways may influence the pharmacodynamic action of drugs. After a usual dose, variations in drug toxicity and inefficacy can be observed depending on the polymorphism, the analgesic considered and the presence or absence of active metabolites. For opioids, the most studied being morphine, mutations in the ABCB1 gene, coding for P-glycoprotein (P-gp), and in the µ-opioid receptor reduce morphine potency. Cytochrome P450 (CYP) 2D6 mutations influence the analgesic effect of codeine and tramadol, and polymorphism of CYP2C9 is potentially linked to an increase in nonsteroidal anti-inflammatory drug-induced adverse events. Furthermore, drug interactions can mimic genetic deficiency and contribute to the variability in response to analgesics. This review summarizes the available data on the pharmacokinetic and pharmacodynamic consequences of known polymorphisms of drug-metabolizing enzymes, drug transporters, drug targets and other nonopioid biological systems on central and peripheral analgesics.

Primary hepatocytes: current understanding of the regulation of metabolic enzymes and transporter proteins, and pharmaceutical practice for the use of hepatocytes in metabolism, enzyme induction, transporter, clearance, and hepatotoxicity studies

This review brings you up-to-date with the hepatocyte research on: 1) in vitro-in vivo correlations of metabolism and clearance; 2) CYP enzyme induction, regulation, and cross-talk using human hepatocytes and hepatocyte-like cell lines; 3) the function and regulation of hepatic transporters and models used to elucidate their role in drug clearance; 4) mechanisms and examples of idiosyncratic and intrinsic hepatotoxicity; and 5) alternative cell systems to primary human hepatocytes. We also report pharmaceutical perspectives of these topics and compare methods and interpretations for the drug development process.

Effect of DPC 333 [(2R)-2-{(3R)-3-amino-3-[4-(2-methylquinolin-4-ylmethoxy)phenyl]-2-oxopyrrolidin-1-yl}-N-hydroxy-4-methylpentanamide], a human tumor necrosis factor alpha-converting enzyme inhibitor, on the disposition of methotrexate: a transporter-based drug-drug interaction case study

DPC 333 [(2R)-2-{(3R)-3-amino-3-[4-(2-methylquinolin-4-ylmethoxy)phenyl]-2-oxopyrrolidin-1-yl}-N-hydroxy-4-methylpentanamide] is a potent human tumor necrosis factor alpha-converting enzyme inhibitor with potential therapeutic implications for rheumatoid arthritis. Methotrexate (MTX), a drug for the treatment of rheumatoid arthritis, is eliminated primarily unchanged via renal and biliary excretion in humans as well as in rats and dogs. The objective of the present study was to investigate the potential effect of DPC 333 on the disposition of MTX. In dogs, DPC 333 administered orally at 1.7 mg/kg 15 min before the intravenous administration of [14C]MTX (0.5 mg/kg) did not alter the plasma concentration-time profile of MTX; however, the total amount of radioactivity excreted in urine increased from 58.7% to 92.2% of the dose, and the renal clearance increased from 1.8 ml/min/kg to 2.9 ml/min/kg, suggesting a decrease in MTX disposition via biliary excretion. The biliary excretion of MTX was investigated in isolated perfused livers prepared from wild-type and TR(-) [multidrug resistance-associated protein 2 (Mrp2)-deficient] Wistar rats in the absence and presence of DPC 333. Mrp2-mediated biliary excretion of MTX was confirmed with 95.8% and 5.1% of MTX recovered in the bile of wild-type and TR(-) Wistar rats, respectively. DPC 333 at an initial perfusate concentration of 50 microM completely blocked the biliary excretion of MTX, but not the clearance from perfusate, in both wild-type and TR(-) rats. These results suggest that the enhanced renal elimination of MTX may be due to the potent inhibition of biliary excretion and active renal reabsorption by DPC 333 and/or its metabolites.

Clinical drug interactions in outpatients of a university hospital in Thailand

BACKGROUND

A clinical event is likely to occur in patients receiving a pair of drugs, that have the potential to cause an interaction. The occurrence of a clinical drug-drug interaction in outpatients of university hospitals in Thailand is unknown.

PURPOSE

To investigate the occurrence of a clinical event associated with drug-drug interactions in outpatients at a Thai university hospital.

METHODS

A case-control study was established. The case was a sample group, randomly selected from a 1-year sample of outpatient prescriptions containing 'significance-1' potential drug-drug interactions, whereas the control was from the same year but with no potential drug interactions. Medical records of the cases and the controls were reviewed for an adverse event (AE) using a newly developed review form. The odds ratio of occurrence of the AE between the cases and the controls was determined. The AE was assessed for its possibility of being caused from a drug-drug interaction.

RESULTS

The most common specific AE in both the cases and the controls was cough. An unplanned revisit to outpatient department or emergency room was found to be the most common general AE. The odds ratio of the occurrence of an AE in the cases, compared with the controls, was 1.495 (95% CI: 0.917-2.438). The possibility that the AEs resulted from drug interactions in the case group was nine 'probable' patients and 15 'possible' patients, whereas that in the control group was eight 'possible' patients. The most common interacting drug pair was isoniazid-rifampin with an increase in serum hepatic enzymes as the corresponding AE.

CONCLUSIONS

Despite outpatients receiving drug pairs with a high potential for adverse interactions, the rate of occurrence of clinical drug interaction events was low.

Evaluation of drug-drug interaction in the hepatobiliary and renal transport of drugs

Recent studies have revealed the import role played by transporters in the renal and hepatobiliary excretion of many drugs. These transporters exhibit a broad substrate specificity with a degree of overlap, suggesting the possibility of transporter-mediated drug-drug interactions with other substrates. This review is an overview of the roles of transporters and the possibility of transporter-mediated drug-drug interactions. Among the large number of transporters, we compare the Ki values of inhibitors for organic anion transporting polypeptides (OATPs) and organic anion transporters (OATs) and their therapeutic unbound concentrations. Among them, cephalosporins and probenecid have the potential to produce clinically relevant OAT-mediated drug-drug interactions, whereas cyclosporin A and rifampicin may trigger OATP-mediated ones. These drugs have been reported to cause drug-drug interactions in vivo with OATs or OATP substrates, suggesting the possibility of transporter-mediated drug-drug interactions. To avoid adverse consequences of such transporter-mediated drug-drug interactions, we need to be more aware of the role played by drug transporters as well as those caused by drug metabolizing enzymes.

Organic anion transporter (Slc22a) family members as mediators of toxicity

Exposure of the body to toxic organic anions is unavoidable and occurs from both intentional and unintentional sources. Many hormones, neurotransmitters, and waste products of cellular metabolism, or their metabolites, are organic anions. The same is true for a wide variety of medications, herbicides, pesticides, plant and animal toxins, and industrial chemicals and solvents. Rapid and efficient elimination of these substances is often the body's best defense for limiting both systemic exposure and the duration of their pharmacological or toxicological effects. For organic anions, active transepithelial transport across the renal proximal tubule followed by elimination via the urine is a major pathway in this detoxification process. Accordingly, a large number of organic anion transport proteins belonging to several different gene families have been identified and found to be expressed in the proximal nephron. The function of these transporters, in combination with the high volume of renal blood flow, predisposes the kidney to increased toxic susceptibility. Understanding how the kidney mediates the transport of organic anions is integral to achieving desired therapeutic outcomes in response to drug interactions and chemical exposures, to understanding the progression of some disease states, and to predicting the influence of genetic variation upon these processes. This review will focus on the organic anion transporter (OAT) family and discuss the known members, their mechanisms of action, subcellular localization, and current evidence implicating their function as a determinant of the toxicity of certain endogenous and xenobiotic agents.

Fever as a risk factor causing delayed elimination of methotrexate in pediatric patients receiving high doses of cancer chemotherapy

PURPOSE

Delayed elimination of methotrexate (MTX) has been reported to be caused by a number of factors. In order to identify these causes, we retrospectively investigated the risk factors for delayed elimination in pediatric patients who received high doses of MTX.

SUBJECTS AND METHODS

The study included 69 courses of therapy involving 22 patients who received more than 1000 mg/m(2) of MTX. Plasma MTX concentrations 48 h (C48) and 72 h (C72) after infusion were used as indices of MTX elimination.

RESULTS

Neither C48 nor C72 was directly proportional to the dose of MTX infused. Both C48 and C72 were significantly higher in patients who developed fever of above 38 degrees C within a 10-day period (i.e., from 7 days before to 3 days after infusion) than in patients with no fever. Subgroup analysis revealed that C72 was significantly higher in patients who either developed fever and received antipyretics or developed fever but did not receive antipyretics than in patients who did not develop fever and did not receive antipyretics. Changes in the serum creatinine concentrations before and after MTX infusion revealed that renal function was significantly decreased in patients who developed fever compared to patients without fever.

CONCLUSIONS

The present results suggest that the development of fever is one of the main risk factors for the delayed elimination of MTX.

Methotrexate-Loxoprofen Interaction: Involvement of Human Organic Anion Transporters hOAT1 and hOAT3

Human organic anion transporters hOAT1 (SLC22A6) and hOAT3 (SLC22A8) are responsible for renal tubular secretion of an antifolic acid methotrexate, and are considered to be involved in drug interaction of methotrexate with nonsteroidal anti-inflammatory drugs (NSAIDs). In our hospital, a delay of methotrexate elimination was experienced in a patient with Hodgkin's disease, who took loxoprofen, a commonly used NSAID in Japan, which suggested a cause. In this study, we examined the drug interaction via hOAT1 and hOAT3, using Xenopus laevis oocytes. hOAT1 and hOAT3 mediated the methotrexate transport with low affinity (K(m) of 724.0 muM) and high affinity (K(m) of 17.2 muM), respectively. Loxoprofen and its trans-OH metabolite, an active major metabolite, markedly inhibited the methotrexate transport by both transporters. Their inhibition concentrations (IC(50)) were in the range of the therapeutic levels. These findings suggest that loxoprofen retards the elimination of methotrexate, at least in part, by inhibiting hOAT1 and hOAT3.

Protein kinase C activation downregulates human organic anion transporter 1-mediated transport through carrier internalization

Organic anion transport in intact renal proximal tubule cells in animal model systems is downregulated by treatments that activate protein kinase C (PKC). How this downregulation is achieved is not yet known. Stimulation of PKC with sn-1,2-dioctanoylglycerol resulted in strong inhibition of p-aminohippurate transport mediated by the cloned human organic anion transporter 1 (hOAT1) expressed in Xenopus oocytes and HEK293 cells, as well as hOAT1 internalization in both expression systems. The sn-1,2-dioctanoylglycerol-induced transport inhibition was partially prevented by staurosporine. It was independent of the conserved canonical PKC consensus sites in hOAT1, however, and was unaffected by agents that destabilize actin filaments or microtubules, which altered baseline hOAT1-mediated p-aminohippurate uptake activity in oocytes. It is concluded that PKC-induced hOAT1 downregulation is achieved through carrier retrieval from the cell membrane and does not involve phosphorylation of the predicted classic hOAT1 PKC consensus sites.

Chemosensitization of Plasmodium falciparum by probenecid in vitro

Resistance to drugs can result from changes in drug transport, and this resistance can sometimes be overcome by a second drug that modifies the transport mechanisms of the cell. This strategy has been exploited to partly reverse resistance to chloroquine in Plasmodium falciparum. Studies with human tumor cells have shown that probenecid can reverse resistance to the antifolate methotrexate, but the potential for reversal of antifolate resistance has not been studied in P. falciparum. In the present study we tested the ability of probenecid to reverse antifolate resistance in P. falciparum in vitro. Probenecid, at concentrations that had no effect on parasite viability alone (50 microM), was shown to increase the sensitivity of a highly resistant parasite isolate to the antifolates pyrimethamine, sulfadoxine, chlorcycloguanil, and dapsone by seven-, five-, three-, and threefold, respectively. The equivalent effects against an antifolate-sensitive isolate were activity enhancements of approximately 3-, 6-, 1.2-, and 19-fold, respectively. Probenecid decreased the level of uptake of radiolabeled folic acid, suggesting a transport-based mechanism linked to folate salvage. When probenecid was tested with chloroquine, it chemosensitized the resistant isolate to chloroquine (i.e., enhanced the activity of chloroquine). This enhancement of activity was associated with increased levels of chloroquine accumulation. In conclusion, we have shown that probenecid can chemosensitize malaria parasites to antifolate compounds via a mechanism linked to reduced folate uptake. Notably, this effect is observed in both folate-sensitive and -resistant parasites. In contrast to the activities of antifolate compounds, the effect of probenecid on chloroquine sensitivity was selective for chloroquine-resistant parasites (patent P407595GB [W. P. Thompson & Co., Liverpool, United Kingdom] has been filed to protect this intellectual property).

Impaired tubular excretory function as a late renal side effect of chemotherapy in children

PURPOSE

Renal drug excretion is variously influenced by nephrotoxic drugs. This study was designed to evaluate renal function as a late renal side effects in children receiving combination chemotherapy for malignancy.

PATIENTS AND METHODS

Follow-up studies of 30 newly diagnosed patients were performed a median of 12 months after completion of chemotherapy. The glomerular filtration rate (GFR) was measured using sodium thiosulfate. The following were also assessed: urinary high-molecular-weight fraction (urinary albumin/urinary creatinine ratio); para-aminohippurate (PAH) clearance; urinary low-molecular-weight fraction (urinary beta2-microglobulin/urinary creatinine ratio); and routine serum and urinary parameters.

RESULTS

Serum and urinary electrolytes were normal in most patients. GFR was low in four patients (13%). Urinary high-molecular-weight fraction was elevated in two patients. Urinary low-molecular-weight fraction was elevated in one patient. PAH clearance was below the referenced normal value in 73% of the patients.

CONCLUSIONS

This report demonstrates decreased PAH clearance as a late renal side effect of chemotherapy and suggests disturbed function of the organic anion transport system. The unexpected high serum concentration of drugs excreted through the organic anion transport system may induce severe side effects. Elucidation of the mechanism and clinical relevance of decreased PAH clearance is warranted.

Studies on the metabolic fate of M17055, a novel diuretic (6). Assessment for drug-drug interactions of M17055 in metabolism, distribution and excretion

1. The potential of M17055, a novel diuretic candidate, to affect the activities of human CYP enzymes, alter the plasma unbound fraction and compete with concomitant drugs in renal secretion as part of an assessment for drug-drug interactions in metabolism, distribution and excretion was investigated. 2. The effects of M17055 on the activities of human CYP1A2, CYP2E1, CYP2C9, CYP2C19, CYP2D6 and CYP3A4 were considered negligible at clinically relevant concentrations. 3. The majority of M17055 (99%) was bound to human plasma proteins, but it is unlikely to alter the binding of other clinically relevant drugs. 4. The renal clearance of M17055 (corrected for the plasma unbound fraction in male rats) substantially exceeded the glomerular filtration rate and was markedly reduced by treatment with probenecid, suggesting that the renal excretion of M17055 is controlled predominantly by an active secretion mechanism. 5. The results show that M17055 is unlikely to cause or undergo significant pharmacokinetic interactions with concomitant drugs in metabolism and distribution. However, when it is administered simultaneously with certain organic anions, drug-drug interactions during kidney excretion may be possible.

Interactions of human organic anion transporters and human organic cation transporters with nonsteroidal anti-inflammatory drugs

The purpose of this study was to elucidate the interactions of human organic anion transporters (hOATs) and human organic cation transporters (hOCTs) with nonsteroidal anti-inflammatory drugs (NSAIDs) using cells stably expressing hOATs and hOCTs. NSAIDs tested were acetaminophen, acetylsalicylate, salicylate, diclofenac, ibuprofen, indomethacin, ketoprofen, mefenamic acid, naproxen, piroxicam, phenacetin, and sulindac. These NSAIDs inhibited organic anion uptake mediated by hOAT1, hOAT2, hOAT3, and hOAT4. By comparing the IC(50) values of NSAIDs for hOATs, it was found that hOAT1 and hOAT3 exhibited higher affinity interactions with NSAIDs than did hOAT2 and hOAT4. HOAT1, hOAT2, hOAT3, and hOAT4 mediated the uptake of either ibuprofen, indomethacin, ketoprofen, or salicylate, but not acetylsalicylate. Although organic cation uptake mediated by hOCT1 and hOCT2 was also inhibited by some NSAIDs, hOCT1 and hOCT2 did not mediate the uptake of NSAIDs. In conclusion, hOATs and hOCTs interacted with various NSAIDs, whereas hOATs but not hOCTs mediated the transport of some of these NSAIDs. Considering the localization of hOATs, it was suggested that the interactions of hOATs with NSAIDs are associated with the pharmacokinetics and the induction of adverse reactions of NSAIDs.