Renal elimination of a novel and potent alphavbeta3 integrin antagonist in animals

Compound A (3-{2-oxo-3-[3-(5,6,7,8-tetrahydro-[1,8]napthyridin-2-yl)propyl]-imidazolidin-1-yl}-3(S)-(6-methoxy-pyridin-3-yl)propionic acid), a hydrophilic zwitter-ion, is a potent and selective alphavbeta3 integrin antagonist currently under clinical development for the treatment of osteoporosis. The mechanism of renal excretion of compound A was investigated using a combination of in vivo and in vitro approaches. In rats, renal excretion of compound A involved tubular secretion; ratios between renal clearance, corrected for unbound fraction in plasma (CLr,u) and glomerular filtration rate (GFR) were greater than unity (2-5). The tubular secretion of compound A was saturable at high plasma levels (> 26 microM), and was inhibited significantly, although modestly (about twofold) by relatively high plasma concentrations of the organic anion PAH (160 microM) and the cation cimetidine (about 400 microM), but not by the P-gp inhibitor quinidine (about 50 microM). However, compound A (about 100 microM) had a minimal effect on CLr/GFRs for cimetidine and PAH. In rhesus monkeys, renal elimination of compound A also involved tubular secretion, with a CLr,u/GFR ratio of about 30. The renal secretion of compound A was not affected by either cimetidine (about 120 microM) or PAH (about 80 microM). Similarly, compound A (about 40 microM) had a minimal effect on the renal tubular secretion of both cimetidine and PAH. At the doses studied, neither rat nor monkey plasma protein binding of compound A, cimetidine or PAH was affected in the presence of each other. In vitro transport studies showed that compound A was not a substrate for P-gp in the Caco-2, human MDR1 and mouse mdr1a transfected LLC-PK1 cell lines. In an uptake study using rOAT1 and rOAT3 transfected HEK cell lines, compound A was shown to be a substrate for rat OAT3 (Km= 15 microM), but not rat OAT1. The results suggest that the tubular secretion of compound A is not mediated by P-gp, but rather is mediated, at least in part, via the organic anion transporter OAT3, the renal transporter shown to be capable of transporting both the organic anion PAH and the organic cation cimetidine. Although there is a possibility for pharmacokinetic interactions between compound A and substrates or inhibitors of OAT3, at the renal excretion level, the magnitude of interaction would likely be modest in humans at clinically relevant doses.     

Saturable Urinary Excretion Kinetics of Famotidine in the Dog

An important elimination route of the histamine H₂ antagonist famotidine is active tubular secretion via the renal organic cation transport system. To characterize the excretion kinetics of famotidine in-vivo, the relationship between plasma concentration and urinary excretion rate was investigated in the beagle dog over a wide concentration range. The maximum transport capacity and the apparent Michaelis–Menten constant of tubular secretion were estimated. Concentration-dependent renal clearance was determined either after intravenous infusion of high doses of famotidine for a short time or during continuous infusion. From individual experiments only indications of saturation were observed; these could not be quantified. A tubular titration curve, in which the active tubular famotidine secretion was plotted against the plasma concentration, was constructed from the data from all the experiments. Active tubular secretion was calculated for each experiment separately by subtracting the famotidine filtration rate from the total excretion rate. A tubular transport maximum of 2400 ± 220 μg min^?1 and an apparent Michaelis–Menten constant for tubular secretion of 26 ± 4 μg mL^?1 (76 ± 12 μm) were estimated from the curve. To the best of our knowledge, this is the first time that saturation of famotidine renal clearance has been fully quantified in-vivo. Considering the low therapeutic plasma concentrations of famotidine (< 0.1 μg mL^?1), these results suggest that clinically the drug has a low interactive potential.     

Renal elimination of a novel and potent αvβ3 integrin antagonist in animals

1. Compound A (3-{2-oxo-3-[3-(5,6,7,8-tetrahydro-[1,8]napthyridin-2-yl)propyl]-imidazolidin-1-yl}-3(S)-(6-methoxy-pyridin-3-yl)propionic acid), a hydrophilic zwitterion, is a potent and selective α_vβ₃ integrin antagonist currently under clinical development for the treatment of osteoporosis. The mechanism of renal excretion of compound A was investigated using a combination of in vivo and in vitro approaches.

2. In rats, renal excretion of compound A involved tubular secretion; ratios between renal clearance, corrected for unbound fraction in plasma (CL_r,u) and glomerular filtration rate (GFR) were greater than unity (2–5). The tubular secretion of compound A was saturable at high plasma levels (>?26?μM), and was inhibited significantly, although modestly (about twofold) by relatively high plasma concentrations of the organic anion PAH (160?µM) and the cation cimetidine (about 400?μM), but not by the P-gp inhibitor quinidine (about 50?μM). However, compound A (about 100?μM) had a minimal effect on CL_r/GFRs for cimetidine and PAH.

3. In rhesus monkeys, renal elimination of compound A also involved tubular secretion, with a CL_r,u/GFR ratio of about 30. The renal secretion of compound A was not affected by either cimetidine (about 120?μM) or PAH (about 80?μM). Similarly, compound A (about 40?μM) had a minimal effect on the renal tubular secretion of both cimetidine and PAH.

4. At the doses studied, neither rat nor monkey plasma protein binding of compound A, cimetidine or PAH was affected in the presence of each other.

5. In vitro transport studies showed that compound A was not a substrate for P-gp in the Caco-2, human MDR1 and mouse mdr1a transfected LLC-PK1 cell lines. In an uptake study using rOAT1 and rOAT3 transfected HEK cell lines, compound A was shown to be a substrate for rat OAT3 (K_m?=?15?μM), but not rat OAT1.

6. The results suggest that the tubular secretion of compound A is not mediated by P-gp, but rather is mediated, at least in part, via the organic anion transporter OAT3, the renal transporter shown to be capable of transporting both the organic anion PAH and the organic cation cimetidine. Although there is a possibility for pharmacokinetic interactions between compound A and substrates or inhibitors of OAT3, at the renal excretion level, the magnitude of interaction would likely be modest in humans at clinically relevant doses.

     

Effect of H2 antagonists on the differential secretion of triamterene and its sulfate conjugate metabolite by the isolated perfused rat kidney.

The isolated perfused rat kidney model was used to examine the effect of the histamine H2 antagonists cimetidine, ranitidine, and famotidine and the organic anion inhibitor probenecid on the differential renal handling of triamterene and its active metabolite p-hydroxytriamterene sulfate. The kidneys were perfused with a Krebs-Henseleit buffer containing albumin, glucose, and amino acids to pH 7.4, and drug concentrations were measured by HPLC. At an initial triamterene concentration of 0.5 mg/liter, the unbound renal clearance to glomerular filtration rate (GFR) ratio was 11.0 +/- 2.5 (mean +/- SD): 1, indicating substantial tubular secretion of the drug. Cimetidine and ranitidine reduced the tubular secretion by about 80% (p less than 0.01), famotidine by between 35 and 60% (p = 0.05), whereas probenecid had no inhibitory effect. For p-hydroxytriamterene sulfate, its unbound renal clearance to GFR ratio was 41 +/- 25:1; this was not affected by cimetidine, ranitidine, or famotidine, whereas probenecid significantly (p less than 0.01) reduced the rate of tubular secretion by 80%. These data indicate that the renal tubular secretion of triamterene is mediated by the organic cation system, whereas for p-hydroxytriamterene sulfate its tubular secretion is via the organic anion system. Famotidine is a weaker inhibitor of the organic cation system compared with cimetidine and ranitidine. These results have implications for drug-drug interaction studies involving renal elimination pathways.     

The mechanism of the renal excretion of disopyramide in rats. I]

The mechanism involved in the renal excretion of disopyramide (DPM) is still incompletely understood. The purpose of this study was to examine the renal handling of DPM and the interactions between DPM and several organic anionic or cationic drugs related to the renal tubular secretion, using the renal clearance and renal cortical slices uptake techniques in rats. The clearance ratio of DPM was greater than that of glomerular filtration and this suggests the tubular secretion of DPM. The clearance ratio of DPM did not change after infusion of either anionic drugs (p-aminohippurate and probenecid) or a cationic drug (cimetidine). The results of time and concentration-dependent experiments using renal cortical slices demonstrated that DPM was accumulated against a concentration gradient by a saturable process. Inhibition of uptake by 2,4-dinitrophenol and cyanide indicated an energy dependence. DPM uptake was considerably inhibited by the cationic drugs, cimetidine and quinine, suggesting that DPM was transported by the cation transport mechanism. Probenecid, a competitor for the anion transport mechanism, moderately inhibited DPM uptake.     

The influence of trimethoprim,sulfamethoxazole, and creatinine on renal organic anion and cation transport in rat kidney tissue

The use of combined trimethoprim and sulfamethoxazole has been reported to increase serum creatinine concentrations in patients by inhibiting creatinine excretion. In confirmation, we found that trimethoprim given over 24 hr to rats augmented serum creatinine concentrations and decreased creatinine clearance relative to urea clearance. Previously, decreased urinary excretion has been hypothesized to occur secondarily to inhibited renal secretory transport of creatinine via the organic cation pathway, although there was no direct evidence to indicate that trimethoprim inhibits organic cation secretion. Such a mechanism is possible because other studies have shown that creatinine is secreted through both the organic anion and cation pathways. We followed organic anion ([³H]PAH) and organic cation ([¹⁴C]TEA) accumulation in incubating rat renal fragments in order to determine whether inhibition of organic cation accumulation by trimethoprim actually does occur. The present investigation shows that trimethoprim interferes with organic cation uptake in vitro but does not influence organic anion uptake. Sulfamethoxazole affected neither organic cation nor anion accumulation significantly. Trimethoprim decreased influx of [¹⁴C]TEA, not its efflux. Other metabolic processes such as QO₂, ammoniagenesis, and gluconeogenesis were not altered greatly by trimethoprim. Creatinine itself decreased organic anion and cation transport through competitive inhibition. Added to the findings that trimethoprim elevates serum creatinine in man without changing glomerular filtration rate, our results strengthen the hypothesis that trimethoprim can decrease serum creatinine excretion through the inhibition of creatinine secretion via the organic cation transport route.     

In-vitro potencies of histamine H2-receptor antagonists on tetraethylammonium uptake in rat renal brush-border membrane vesicles

Abstract— The histamine H₂ antagonists cimetidine, ranitidine and famotidine are organic bases that are cleared from the body by active renal tubular secretion involving the organic cation transporter in the proximal tubule. To determine the potential for competition for the transporter between these drugs and other drugs, their inhibitory potencies were assessed in-vitro, using rat renal brush-border membrane vesicles and tetraethylammonium as the substrate. The concentration-dependent effect of cimetidine, ranitidine and famotidine on the 15-s proton-stimulated uptake of tetraethylammonium into the membrane vesicles was studied using five different rat kidneys. The order of inhibition potencies was: cimetidine (mean IC50= 1·07 μm ) > famotidine (2·43 μm ) > ranitidine (55·4 μm ). The results indicate the potential for drug interactions in the kidney, especially for cimetidine and famotidine.     

Renal tubular secretion of amiloride and its inhibition by cimetidine in humans and in an animal model

The histamine H2 antagonist cimetidine has been shown to reduce the renal tubular secretion of other organic cations through competition for the specific transport system with organic cations in the renal proximal tubule. The potential interaction between cimetidine and the potassium-sparing diuretic amiloride was investigated in humans and in the isolated perfused rat kidney. A chronic dosing study was conducted in eight healthy subjects who received, in random order, amiloride (5 mg daily), cimetidine (400 mg twice daily), both drugs together, and a control phase in which no drug was present. Cimetidine reduced the renal clearance of amiloride by a mean of 17%, from 358 +/- 134 to 299 +/- 118 ml/min (p less than 0.05), and the urinary excretion of amiloride from 65 +/- 11 to 53 +/- 13% of the dose (p less than 0.05). Amiloride reduced the excretion of cimetidine from 43 +/- 7 to 32 +/- 9% of the dose (p less than 0.05) and the area under the plasma concentration-time curve for cimetidine by a mean of 14% (p less than 0.05) but had no effect on the renal clearance of cimetidine. In the perfused rat kidney, cimetidine reduced the amiloride unbound renal clearance to glomerular filtration rate ratio from 5-7:1 to 1-2:1 (p less than 0.05). These studies demonstrate that cimetidine inhibits the renal tubular secretion of amiloride in humans and in rats to a similar extent. In addition, in humans the gastrointestinal absorption of both amiloride and cimetidine appear to be reduced by each other, by an as yet unknown mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)     

Renal secretion of purine nucleosides and their analogs in mice

Previous results have indicated that 2'-deoxyadenosine (dAdo) and 2'-deoxytubercidin (dTub) are secreted by the mouse kidney. Secretion of dTub appeared to occur via the organic cation carrier [J. F. Kuttesch, Jr. et al., Biochem. Pharmac. 31, 3387 (1982)]. In the current study, the structural specificity of the secretory system for d Tub was probed by evaluating the renal clearance of several sugar-modified dTub analogs. The following sugar-modified derivatives also underwent apparent secretion: 3'-deoxy, arabinosyl, and xylosyl. These results suggest a lack of structural specificity of the secretory system for dTub. Tubercidin was apparently reabsorbed, analogous to the observation in mice that adenosine clearance is less than that of inulin. In related experiments, a transport maximum for dAdo could not be demonstrated due to the marked pharmacologic activity of dAdo. Cimetidine was found to selectively inhibit the organic cation secretory system since it blocked the renal secretion of tetraethylammonium but not that of p-amminohippurate in mice. Correspondingly, cimetidine prevented the renal secretion dTub; however, cimetidine did not inhibit the renal secretion of dAdo nor the renal reabsorption of Ado. These results suggest that renal secretion of dTub occurs via the organic cation carrier. The mechanisms for the renal secretion of dAdo and for the renal reabsorption of Ado may be unique and independent of the organic cation system.     

Urinary excretion kinetics of famotidine in rats

Famotidine is a new histamine H2-receptor antagonist which has been demonstrated to be more potent than cimetidine and ranitidine in inhibiting gastric acid secretion. Nine groups of adult male Sprague-Dawley rats received an ia injection of various loading doses of famotidine followed immediately by a constant infusion of the drug at different rates for 6 hr. When steady state famotidine concentrations in plasma were low, renal clearance of the drug (CLR) was greater than glomerular filtration (GFR), and the ratio CLR/GFR was about 4.5 at plasma concentrations of 0.2-1.8 micrograms/ml, suggesting that famotidine was actively secreted by the renal tubules. The CLR decreased as famotidine concentration in plasma increased, and the ratio CLR/GFR approached 1 in the concentration range of 25-76 micrograms/ml, thus providing evidence for saturation of the secretory mechanism. The maximum rate of secretory transport (Tm) of famotidine averaged 180 micrograms/min/kg. On average, some 50-70% of an ia bolus dose was excreted in the urine as unchanged drug within 24 hr of administration. Over the dose range of 0.3-30 mg/kg famotidine, there was no dose-dependent effect on total or renal clearance. Since the lowest dose level, 0.3 mg/kg, is below the recommended human therapeutic dose for famotidine (0.6 mg/kg), the saturation of the renal excretion process observed here in rats is not likely to be of clinical significance.     

Comparative effect of famotidine and cimetidine on the pharmacokinetics of theophylline in normal volunteers.

The comparative effect of famotidine or cimetidine on theophylline disposition was determined in healthy volunteers. Cimetidine, but not famotidine, caused a reduction in the rate of elimination of theophylline. The mean total body clearance of theophylline was reduced from 57.6 ml min-1 before cimetidine to 39.5 ml min-1 during cimetidine; and the half-life was prolonged from 8.7 h before cimetidine to 12 h during cimetidine. The volume of distribution and renal excretion of theophylline were not affected by either famotidine or cimetidine.     

Evidence for in vivo effect of lithium on p-aminohippurate transport in rat kidney, preliminary study

We examined the effect of lithium on rat renal handling of p-aminohippurate (PAH) and accumulation of organic ions by rat kidney cortical slices. When infused intravenously with lithium at the rate of 0.13 mmoles/kg/min, decreased renal clearance of PAH as well as no significant changes in glomerular filtration rate and plasma PAH level was observed at the first clearance period during lithium infusion. As we expected, tubular secretion of PAH also was decreased significantly by the infusion of lithium. Therefore, it is suggested that the decrease in the clearance of PAH was due to the decrease in the tubular secretion of PAH. After four days of injections with lithium (4 mmoles/kg, i.p., once a day), a significant decrease in PAH accumulation in the slices was detected. No inhibition of tetraethylammonium accumulation was observed. Lithium pretreatment did not alter water content and extracellular space of the slices. The results suggest that lithium selectively inhibits the organic anion transport system in kidney with the in vivo treatment and follows our previous work in which we showed the in vitro effect of lithium on organic anion accumulation in the slices.     

Pharmacokinetic and pharmacodynamic properties of histamine H2-receptor antagonists. Relationship between intrinsic potency and effective plasma concentrations.

Histamine H2-receptor antagonists are a unique class of compounds. Pharmacologically they are characterised as a family by their ability to inhibit the secretion of gastric acid, and kinetically they are classified as a family by their similarity in absorption, distribution and elimination. All the H2-receptor antagonists exhibit classical competitive drug-receptor interactions, with Schild slope parameters not significantly different from unity. Comparison of the values of the negative logarithm of the molar concentration of antagonist in the presence of which the potency of the agonist is reduced 2-fold (PA2) indicates that famotidine is about 20 to 50 times more potent than cimetidine and 6 to 10 times more potent than ranitidine. To date, famotidine is the most potent among marketed H2-receptor antagonists. Oral absorption of all the H2-receptor antagonists under clinical investigation is fairly rapid. Peak plasma concentrations are usually attained within 1 to 3h after the dose, but a second peak after oral administration has been observed with cimetidine, ranitidine, famotidine, ramixotidine and etintidine. The mean oral bioavailability for the H2-antagonists ranges from 50 to 70%. Reports on the plasma profiles after intravenous administration are available only for cimetidine, ranitidine, famotidine and nizatidine: plasma concentrations of all 4 decline in a biexponential manner. All of the H2-antagonists are eliminated quite rapidly, with a terminal half-life of 1 to 3h and a total body clearance of 24 to 48 L/h. Elimination is mainly attributable to renal excretion, with renal clearances ranging from 13.8 to 30 L/h. As the values for renal clearance greatly exceed the glomerular filtration rate (6 to 7.2 L/h), it is apparent that renal tubular secretion plays an important role. There is a simple, direct correlation between plasma concentrations of H2-receptor antagonists and the inhibition of gastric acid secretion. This implies a rapid equilibration between drug concentration in plasma and at the site of action, and a reversible drug-receptor interaction. Success in correlating the plasma concentration of H2-receptor antagonists and their pharmacological effects stems from reliable and precise measurement of both items. Despite the heterogeneous nature of data sources, 50% inhibitory concentration (IC50) values for cimetidine, ranitidine, famotidine, nizatidine, etintidine and roxatidine obtained in vitro appear to be in good agreement with those determined in vivo. These results suggest that at an early stage of development of an H2-receptor antagonist, IC50 determined from in vitro studies may be useful as a first approximation to predict the clinically effective concentration of the new agent.     

The inhibitory effect of probenecid on renal excretion of famotidine in young, healthy volunteers

Effects of coadministration of probenecid on pharmacokinetic behaviors of famotidine, an H2-receptor antagonist, after oral administration, were studied in eight young, healthy volunteers. They received an oral 20 mg dose of famotidine with and without coadministration of oral 1500 mg doses of probenecid. The mean area under the serum famotidine concentration-time curve up to 10 hours was increased by coadministration of probenecid from 424 +/- 19 (SEM) to 768 +/- 39 ng.hr/ml. The mean urinary excretion rate of unchanged famotidine, the mean amount of unchanged famotidine excreted in urine up to 24 hours and mean renal clearance were decreased by coadministration of probenecid. The mean tubular secretion clearance of famotidine was decreased from 196.2 +/- 21.4 to 22.0 +/- 4.2 ml/min. These data suggest that probenecid, which is a classical inhibitor of renal tubular secretion of organic anions, inhibits the renal tubular secretion of famotidine, which exists partly in a cationic form under physiological pH conditions.     

The effect of famotidine on renal function in patients with renal insufficiency.

The effect of famotidine, a new histamine H2-receptor antagonist, on renal tubular creatinine secretion was evaluated in twelve patients with reduced renal function (creatinine clearance 10-60 ml min-1). Creatinine and inulin clearances were determined at baseline and for 4 h after a 10 mg intravenous dose of famotidine. Famotidine renal clearance exceeded inulin clearance by an average of 152%, indicating that renal tubular secretion of famotidine occurred. No significant changes in the clearances of creatinine or inulin, or the fractional clearance of creatinine were observed after famotidine administration. These data suggest that famotidine, unlike cimetidine, does not inhibit renal tubular secretion of creatinine. Thus, famotidine does not affect creatinine-dependent measurements of renal function and is unlikely to alter the renal elimination of basic drugs.     

Renal excretion of emtricitabine I: effects of organic anion, organic cation, and nucleoside transport inhibitors on emtricitabine excretion

The excretion of emtricitabine (FTC) was characterized using isolated perfused rat kidney (IPK) model. Studies were performed to assess the dose-linearity of FTC excretion, to evaluate the effect of inhibitors of organic anion (probenecid, PBC), organic cation (tetraethylammonium, TEA; cimetidine, CMD) and nucleoside (uridine, URD) transport systems on FTC excretion, and to determine the potential interaction between FTC and trimethoprim (TMP). FTC excretion was studied over a range of doses (80-1600 microg), targeting concentrations encompassing the therapeutic range of FTC (1-20 microg/mL). FTC (2 microg/mL) was also coperfused with PBC (500 microM), TEA (500 microM), CMD (2 mM), URD (500 microM), and TMP (13.7 microM). FTC dose-linearity studies revealed that excretion parameters were not significantly different among dosing groups. Of the transport inhibitors tested, FTC XR decreased more than twofold in the presence of CMD (0.32 +/- 0.099). PBC, TEA, and URD had no observed effect on FTC excretion. TMP coadministration significantly inhibited FTC excretion (XR = 0.43 +/- 0.052). The results suggest that FTC renal transport is likely mediated by a CMD-sensitive organic cation transporter (OCT) in the kidney. TMP may inhibit the renal excretion of FTC when the two compounds are coadministered in vivo.     

Moment analysis of drug disposition in kidney. VI: Assessment of in vivo transmembrane transport of p-aminohippurate in tubular epithelium.

This paper describes a novel method to assess the antiluminal membrane (ALM) and luminal membrane (LM) transport in vivo across renal tubular epithelial cells. The method is based upon a noncompartmental moment analysis of the plasma concentration and urinary excretion rate curves following renal artery injection. Quantitative relationships are represented between the noncompartmental parameters (clearance, volume of distribution, and the mean transit time) and the first-order rate constants associated with transmembrane transport processes. The in vivo transepithelial transport of [14C]p-aminohippurate (PAH) was examined using the rat kidney in the absence or presence of various plasma concentrations of unlabeled PAH, cefazolin, and methotrexate. The tubular secretion intrinsic clearance was reduced with an increase in the plasma concentration of concurrent unlabeled organic anions. The distribution volume of PAH in the kidney decreased in association with a decrease in the amount of PAH secreted, whereas the mean transepithelial (artery-to-lumen) transit time (Tcell) remained constant. These findings indicate that ALM transport is a capacity-limited process determining the amount of tubular secretion, and that LM transport is linear over the concentration range examined and independent of the amount of secretion. The contribution of ALM and LM transport to transcellular transport was first clarified in vivo. The present method will be useful for analyzing the transmembrane transport processes in vivo for highly diffusible substances in the kidney.     

The anti-influenza drug oseltamivir exhibits low potential to induce pharmacokinetic drug interactions via renal secretion-correlation of in vivo and in vitro studies.

Oseltamivir is an ester prodrug of the active metabolite [3R,4R,5S]-4-acetamido-5-amino-3-(1-ethylpropoxy)-1-cyclohexene-1-carboxylate phosphate (Ro 64-0802), a potent and selective inhibitor of neuraminidase enzyme of influenza virus. Oseltamivir is rapidly hydrolyzed by hepatic carboxylesterases to Ro 64-0802, which is then exclusively excreted by glomerular filtration and active tubular secretion without further metabolism. In vivo and in vitro studies were conducted to evaluate the renal drug-drug interaction potential of oseltamivir. Crossover studies were conducted in healthy subjects in which oral oseltamivir was administered alone and coadministered with probenecid, cimetidine, or amoxicillin. Probenecid completely blocked the renal secretion of Ro 64-0802, increasing systemic exposure (area under the curve) by 2.5-fold, but no interaction was observed with cimetidine or amoxicillin. These in vivo data show that Ro 64-0802 is secreted via an organic anion pathway, but Ro 64-0802 does not inhibit amoxicillin renal secretion. In vitro effects of Ro 64-0802 on the human renal organic anionic transporter 1 (hOAT1) were investigated using novel Chinese hamster ovary cells stably transfected with hOAT1. Ro 64-0802 was found to be a low-efficiency substrate for hOAT1 and a very weak inhibitor of hOAT1-mediated transport of p-aminohippuric acid (PAH). Ro 64-0802 did not inhibit the hOAT1-mediated transport of amoxicillin. In contrast, probenecid effectively inhibited the transport of PAH, Ro 64-0802, and amoxicillin via hOAT1. These in vitro observations are consistent with the in vivo data, validating the usefulness of the in vitro system for evaluating such drug-drug interaction. The study results demonstrate that oseltamivir has a low drug-drug interaction potential at the renal tubular level due to inhibition of hOAT1.     

L-type fatty acid binding protein transgenic mouse as a novel tool to explore cytotoxicity to renal proximal tubules

A novel biomarker of renal dysfunction, liver-type fatty acid binding protein (L-FABP), which is expressed in human proximal tubules, binds to lipid peroxidation products during renal injury and is excreted into the urine. Here, we examined the usefulness of human L-FABP transgenic (Tg) mice as a tool to explore nephrotoxicity, employing two model drugs, cephaloridine and cisplatin, which are taken up by renal tubules via organic anion and cation transporters, respectively. Urinary excretion of L-FABP increased after administration of cephaloridine in most of the Tg mice, whereas glomerular filtration markers such as blood-urea-nitrogen (BUN) and plasma creatinine (CRE) were almost unchanged. Thus, L-FABP is a highly sensitive detector of the nephrotoxicity of cephaloridine. Urinary excretion of L-FABP in the Tg mice also increased after administration of cisplatin, and this increase was reduced by coadministration of cimetidine. Both BUN and CRE also increased after the cisplatin treatment, but these parameters were minimally affected by coadministration of cimetidine, suggesting that cimetidine reduces cisplatin-induced renal tubular toxicity with only a minimal effect on the glomerulus. These results indicate that the L-FABP Tg mouse should be a useful drug screening system to evaluate specifically the toxicity of transporter substrates to renal tubules.     

Characterization of renal excretion mechanism for a novel diuretic, M17055, in rats

M17055 was developed as a novel diuretic that inhibits both Na(+), K(+), and 2Cl(-) cotransport at the thick ascending Henle's loop and Na(+) reuptake at the distal tubule. It is secreted at the renal proximal tubules. The purpose of the present study was to characterize the renal excretion mechanism of M17055. We used the renal cortical slices and brush border membrane vesicles (BBMVs) to investigate the transport mechanisms across the basolateral and brush border membranes, respectively. M17055 uptake by rat renal slices increased with time and was saturable. Several organic anions including probenecid, para-aminohippurate (PAH), and estrone-3-sulfate, decreased M17055 uptake. The uptake of M17055 was also observed into HEK293 cells expressing rat OAT1, and was inhibited by PAH. M17055 uptake by BBMVs was time-dependent, saturable, osmolarity-sensitive, and inhibited by several organic anions, but not by PAH. These results suggest that plural organic anion transport systems are involved in M17055 transport via both basolateral and brush border membranes of proximal tubule epithelial cells, a part of the renal uptake being mediated by OAT1.