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PubMed2000

Interactions of the human multidrug resistance proteins MRP1 and MRP2 with organic anions.

The human multidrug resistance protein MRP1 and its homolog, MRP2, are both suggested as being involved in cancer drug resistance and the transport of organic anions. We expressed MRP1 and MRP2 in Spodoptera frugiperda ovarian cells and compared their ATP-dependent transport properties and vanadate-sensitive ATPase activities in isolated membrane vesicles. Both MRP1 and MRP2 actively transported leukotriene C(4) and N-ethylmaleimide glutathione (NEM-GS), although the relative affinity of MRP2 for these substrates was found to be significantly lower than that of MRP1. Methotrexate was actively transported by both proteins, although more efficiently by MRP2. ATP-dependent NEM-GS transport by MRP1 and MRP2 was variably modulated by organic anions. Probenecid and furosemide inhibited, whereas under certain conditions sulfinpyrazone, penicillin G, and indomethacin greatly stimulated, MRP2-mediated NEM-GS uptake. Vanadate-sensitive ATPase activity in isolated membranes containing MRP1 or MRP2 was significantly stimulated by NEM-GS and reduced GS, although these compounds acted only at higher concentrations in MRP2. ATP hydrolysis by MRP2 was also effectively stimulated by methotrexate. Probenecid, sulfinpyrazone, indomethacin, furosemide, and penicillin G all significantly increased MRP2-ATPase activity, whereas these compounds acted more as ATPase inhibitors on MRP1. These results indicate that MRP1 is a more efficient transporter of glutathione conjugates and free glutathione than MRP2, whereas several anions are preferred substrates for MRP2. Our data suggest that MRP2 may be responsible for the active secretion of pharmacologically relevant organic anions, such as diuretics and antibiotics, and indicate different modulation possibilities for MRP1 or MRP2 in drug-resistant tumor cells.

Adenosine Triphosphatases↗
PubMed1981

Comparative multiple-dose pharmacokinetics of cefotaxime, moxalactam, and ceftazidime.

The pharmacokinetics of cefotaxime, moxalactam, and ceftazidime were investigated in six human volunteers who received in a crossover fashion doses of 0.5, 1.0, and 2.0 g of each drug by a 5-min infusion. Doses of 1.0 g were repeated after the administration of probenecid. Serum and urine concentrations were assayed with an agar diffusion method. Serum concentrations of moxalactam exceeded those of ceftazidime at all times and were distinctly higher than those of cefotaxime. The normalized area under the concentration time curve (defined as the ratio of the area under the curve per dose) reflects this relationship: compared with cefotaxime the normalized area under the curve of moxalactam was 3 to 4 times higher, and that of ceftazidime was 2 to 3 times higher. By intra-individual comparisons, the area under the curve of moxalactam was 44% larger than that of ceftazidime. With increasing doses, cefotaxime exhibited a nonlinear increase of the area under the curve. The half-lives of moxalactam, ceftazidime, and cefotaxime were 2.34, 1.95, and 1.16 h, respectively. The volume of distribution averaged 0.20 +/- 0.03, 0.23 +/- 0.02, and 0.25 +/- 0.04 liters per kg, and the mean total body clearance was 84, 131, and 328 ml/min for moxalactam, ceftazidime, and cefotaxime, respectively. The 24-h urinary recovery was highest for moxalactam (75 +/- 4%) followed by ceftazidime (68 +/- 11%) and cefotaxime (53 +/- 6%). The influence of probenecid on serum concentrations, half-life, area under the curve, and clearance was most apparent with cefotaxime, whereas the pharmacokinetics of moxalactam and ceftazidime were only slightly affected. After the 0.5- and 2.0- g doses of cefotaxime, desacetyl-cefotaxime activity (determined by high-pressure liquid chromatography) reached a peak of 2.7 and 9.9 mug/ml and declined with a half-life of 1.9 and 1.4 h. The ratio of the R(-) and S(-) epimers of moxalactam, which could be differentiated by high-pressure liquid chromatography, fell rapidly from 0.81 at 0.17 h to 0.5 at 5 h, indicating the presence of twice as much of the microbiologically less active S(-) epimer. From a pharmacokinetic standpoint it appears reasonable to conclude that moxalactam and possibly ceftazidime could be administered twice daily and that cefotaxime could be administered three or even four times daily.

Cefotaxime↗
PubMed1992

Pharmacokinetics of R 82913 in AIDS patients: a phase I dose-finding study of oral administration compared with intravenous infusion.

The pharmacokinetics of oral administration of R 82913, or tetrahydroimidazol [4,5,1-jk]-benzodiazepin-2(1H)-one or -thione (TIBO), was compared with those of intravenous administration in five AIDS patients. TIBO was administered as a single daily 1-h infusion of 100 mg for 29 days and orally as a single daily dose for 14 days with three consecutive regimens of 100, 200, and 100 mg with probenecid (1 g) daily. Each cycle was followed by a wash-out period. Oral bioavailability of TIBO appears to be low and is not improved by the adjunction of probenecid. Trough levels obtained with oral administration systematically remained far below the 90% inhibitory concentration of TIBO against human immunodeficiency virus type 1 (HIV-1). Tolerance of TIBO was excellent. No clinical efficacy could be demonstrated. p24 antigenemia decreased significantly in one patient under intravenous therapy. TIBO derivatives are promising anti-HIV-1 agents in vitro, but improvement of oral bioavailability is needed before implementation of long-term efficacy and tolerability studies. Moreover, rapid emergence of resistance, which has been recently documented, constitutes a major problem with most nonnucleoside reverse transcriptase inhibitors.

Acquired Immunodeficiency Syndrome↗
PubMed1997

Safety and pharmacokinetics of CS-834, a new oral carbapenem antibiotic, in healthy volunteers.

CS-834, (+)-[pivaloyloxymethyl (4R,5S,6S)-6-[(R)-1-hydroxyethyl]-4-methyl-7-oxo-3-[[(R)-5-oxopyrroli din-3-yl]thio]-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylate], is an ester-type oral carbapenem prodrug, and an active metabolite is R-95867, which has antibacterial activity. CS-834 was administered orally to healthy male volunteers at single doses of 50, 100, 200, and 400 mg and at a multiple dose of 150 mg three times a day for 7 days to investigate its safety and pharmacokinetic profiles. Other studies were conducted to examine the effect of food intake on the bioavailability of CS-834 and also the effect of the coadministration of probenecid on the pharmacokinetics of CS-834. In the fasting state, the concentration of R-95867 in plasma reached maximum levels from 1.1 to 1.7 h after the oral administration of CS-834, followed by a monoexponential decrease. The maximum concentrations of R-95867 in serum (C[max]s) after the administration of CS-834 at doses of 50, 100, 200, and 400 mg were 0.51, 0.97, 1.59, and 2.51 microg/ml, respectively. The half-lives (t1/2s) were almost constant, approximately 0.7 h. The areas under the concentration-time curves (AUCs) were proportional to the doses, ranging from 50 to 400 mg x h/ml. The cumulative recoveries in urine were approximately 30 to 35% until 24 h after drug administration. The C(max), AUC, t1/2, and recovery in urine were not affected by food intake. Probenecid coadministration prolonged the t1/2, and it increased the C(max) and AUC for R-95867 by approximately 1.5- and 2.1-fold, respectively. The multiple-dose study showed no change in the pharmacokinetics from those for the single doses and no drug accumulation in the body. A mild transient soft stool was observed in one volunteer in the study with a single dose of 400 mg. In the multiple-dose study, mild transient soft stools were observed in six volunteers, one volunteer had mild transient diarrhea, and one volunteer had elevated serum glutamic oxalacetic transaminase and serum glutamic pyruvic transaminase levels (1.4- and 2.8-fold compared with the upper limits of normal, respectively). There were no other abnormal findings for objective symptoms or laboratory findings, including blood pressure, heart rate, electrocardiogram, body temperature, hematology, blood chemistry, and urinalysis.

Administration, Oral↗
PubMed1998

Disposition of the acyclic nucleoside phosphonate (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine.

The acyclic nucleoside phosphonate (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine [(S)-HPMPA] has been shown to be active against pathogens, like hepatitis B viruses and Plasmodium parasites, that infect parenchymal liver cells. (S)-HPMPA is therefore an interesting candidate drug for the treatment of these infections. To establish effective therapeutic protocols for (S)-HPMPA, it is essential that the kinetics of its hepatic uptake be evaluated and that the role of the various liver cell types be examined. In the present study, we investigated the disposition of (S)-HPMPA and assessed its hepatic uptake. Rats were intravenously injected with [3H](S)-HPMPA, and after an initial rapid distribution phase (360 +/- 53 ml/kg of body weight), the radioactivity was cleared from the circulation with a half-life of 11.7 +/- 1.4 min. The tissue distribution of [3H](S)-HPMPA was determined at 90 min after injection (when >99% of the dose cleared). Most (57.0% +/- 1.1%) of the injected [3H](S)-HPMPA was excreted unchanged in the urine. The radioactivity that was retained in the body was almost completely recovered in the kidneys and the liver (68.4% +/- 2.5% and 16.1% +/- 0.4% of the radioactivity in the body, respectively). The uptake of [3H](S)-HPMPA by the liver occurred mainly by parenchymal cells (92.1% +/- 3.4% of total uptake by the liver). Kupffer cells and endothelial cells accounted for only 6.1% +/- 3.5% and 1.8% +/- 0.8% of the total uptake by the liver, respectively. Preinjection with probenecid reduced the hepatic and renal uptake of [3H](S)-HPMPA by approximately 75%, which points to a major role of a probenecid-sensitive transporter in the uptake of (S)-HPMPA by both tissues. In conclusion, we show that inside the liver, (S)-HPMPA is mainly taken up by parenchymal liver cells. However, the level of uptake by the kidneys is much higher, which leads to nephrotoxicity. An approach in which (S)-HPMPA is coupled to carriers that are specifically taken up by parenchymal cells may increase the effectiveness of the drug in the liver and reduce its renal toxicity.

Adenine↗
PubMed1975

Comparative in vitro activity and clinical pharmacology of ticarcillin and carbenicillin.

The in vitro activity and human pharmacology of ticarcillin, a semisynthetic penicillin more active than carbenicillin against Pseudomonas, were compared. There has been no increase in resistance to ticarcillin of Pseudomonas strains over the past 5 years, but resistance of indole-positive Proteus and Serratia strains has been documented. After intramuscular (i.m.) injection of 1 g of ticarcillin, mean peak levels occurred at 1 h (26.9 mug/ml) with a decline over 6 h (6.8 mug/ml). Serum half-life was 84 min. Dilution of ticarcillin lidocaine reduced pain on i.m. injection but did not alter serum levels. Blood levels after 1 g i.m. are adequate to treat infections produced by Escherichia coli, Proteus mirabilis, and some Enterobacter, but not Pseudomonas. After rapid intravenous infusion of 3 and 5 g, mean peak serum levels of ticarcillin were slightly lower for 1 h than those achieved with carbenicillin. Probenecid administered before infusion produced increases in blood levels, half-lives, and volume of distribution. The biological half-life of ticarcillin was 72 min compared to 66 min with carbenicillin. There was a larger volume of distribution for ticarcillin than carbenicillin (15 liters versus 14 liters). The ticarcillin half-life when administered with probenecid was 108 min. Urinary recovery of ticarcillin was 77% against 95% of carbenicillin. However, approximately 10% of ticarcillin is recovered as penicilloic acid so that 95% of an intravenously administered dose is recovered.

Carbenicillin↗
PubMed1985

Survival of treponemes after treatment: comments, clinical conclusions, and recommendations.

Treponemes may persist after treatment that has been accepted as effective; the reasons for this are discussed. Nevertheless, the epidemic of syphilis after the second world war was not followed by an epidemic of late syphilis, and the results of treatment with penicillin are excellent. Neurological signs may progress in some treated patients, and the standard doses of soluble penicillin and any dose of benzathine penicillin (even with added probenecid by mouth) cannot be relied on to achieve treponemicidal concentrations in the cerebrospinal fluid (CSF). There are no large scale studies of CSF findings after treatment of early syphilis with benzathine penicillin. Standard dosage, such as procaine penicillin G 600 000 international units (IU) by intramuscular injection for 10 days, is the treatment of choice for the patient suffering from uncomplicated early syphilis; this should be preferred to benzathine penicillin, which should only be used when standard treatment as above cannot be given. Treponemicidal concentrations of penicillin should be achieved in the CSF of patients suffering from neurosyphilis by schedules of probenecid by mouth and procaine penicillin by single daily intramuscular injections; treatment should last for 17 to 21 days. Benzathine penicillin should not be used for the treatment of patients suffering from neurosyphilis or from the iritis of late syphilis including that accompanying interstitial keratitis. Treatment for interstitial keratitis should initially be as for neurosyphilis, but in recurrent cases it may have to be prolonged to eradicate Treponema pallidum that is dividing slowly. Doxycycline 200 mg by mouth daily for 21 days provides a supervisable outpatient schedule for patients allergic to penicillin. Cephaloridine (and probably cefuroxime and the new cephalosporins) may be useful for patients who are allergic to penicillin but have not developed anaphylactic allergy. If erythromycin is used for treating syphilis in pregnant women who are allergic to penicillin, then the newborn babies should be treated with penicillin.

Animals↗
PubMed1986

Oral cefuroxime axetil compared with oral ampicillin in treating acute uncomplicated gonorrhoea.

The efficacy and tolerance of single oral doses of cefuroxime axetil (1.5 g) were compared with oral ampicillin (3 g) for treating acute gonococcal urethritis in 110 men and 30 women. Each dose was given with 1 g probenecid. Of the 62 assessable patients who received ampicillin, two failed to respond to treatment. Of 67 assessable patients who received cefuroxime axetil, one failed to respond. Pencillinase producing strains of Neisseria gonorrhoeae were isolated from five patients; one received ampicillin and failed to respond, whereas the other four received cefuroxime axetil and three were cured. A single oral dose of 1.5 g cefuroxime axetil with 1 g probenecid seemed to be an effective treatment for acute gonococcal urethritis, especially for penicillin resistant strains.

Adolescent↗
PubMed1993

Synthesis and vectorial export of cGMP in airway epithelium: expression of soluble and CNP-specific guanylate cyclases.

Guanosine 5'-cyclic monophosphate (cGMP) is an important modulator of fluid balance in many epithelia. We examined its metabolism in primary cultures of human airway epithelia. Sodium nitroprusside increased cGMP levels 30-fold, suggesting that the respiratory epithelium expresses a soluble guanylate cyclase; however, endogenous nitric oxide production was not detected. cGMP levels could also be increased by C-type natriuretic peptide (CNP), but not by atrial natriuretic peptide, brain natriuretic peptide, or Escherichia coli heat-stable enterotoxin, indicating expression of a CNP-specific membrane-bound guanylate cyclase. The one-half effective concentration for CNP was 40 nM and the maximal velocity was 56.7 pmol cGMP.mg protein-1.h-1. After CNP stimulation, approximately 60% of the total synthesized cGMP was preferentially exported from the polarized epithelial cells across the basolateral membrane by a probenecid-sensitive process. Isoproterenol-stimulated adenosine 3',5'-cyclic monophosphate (cAMP) export revealed a similar export pattern and probenecid sensitivity, although a lower efficiency of export (27% of total cAMP was exported). Consistent with previous reports, export of neither cyclic nucleotide was saturable at the concentrations tested. We conclude that the respiratory epithelium expresses a soluble guanylate cyclase, a CNP-specific receptor, and a novel vectorial cyclic nucleotide export mechanism.

1-Methyl-3-isobutylxanthine↗
PubMed2002

Transepithelial organic anion transport by shark choroid plexus.

Spiny dogfish shark (Squalus acanthias) lateral and IV choroid plexuses (CPs) are ultrastructurally similar to the corresponding tissues of rat. However, shark IV CP is proportionally larger and easily accessible. Moreover, this epithelial sheet can be halved and studied in Ussing flux chambers. We have used confocal fluorescence microscopy and radiotracer techniques to characterize transepithelial transport of the organic anions (OAs) fluorescein (FL) and 2,4-dichlorophenoxyacetic acid (2,4-D), respectively, by shark CP. Lateral and IV CP accumulated 1 microM FL, with highest levels in the underlying extracellular spaces, intermediate levels in epithelial cells, and lowest levels in the medium. 2,4-D and probenecid inhibited FL accumulation in cells and extracellular spaces, suggesting that these substrates compete for common carriers. Unidirectional absorptive [cerebrospinal fluid (CSF)-to-blood] and secretory (blood-to-CSF) fluxes of 10 microM [(14)C]2,4-D were measured under short-circuited conditions in IV CP mounted in Ussing chambers. 2,4-D underwent net absorption, with an average flux ratio of 7. Probenecid, 2,4,5-trichlorophenoxyacetic acid, and 5-hydroxyindolacetic acid reduced net absorption, reversibly inhibiting unidirectional absorption, with no effect on secretion. Ouabain irreversibly reduced net 2,4-D absorption and cellular and extracellular accumulation of FL, suggesting energetic coupling of OA absorption to Na(+) transport. Collectively, these data indicate that shark CP actively removes OAs from CSF by a process that is specific and active.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1991

Taurine secretion in cultured winter flounder renal epithelium.

The mechanism for the secretion of taurine by the marine fish kidney was examined in flounder renal primary cultures and teased tubules. The question addressed was whether the secretion of taurine, but not beta-alanine, a related beta-amino acid, is due to differences in their basolateral uptake, intracellular concentration, or luminal efflux mechanism. Aminooxyacetate (AOA) (10 mM), an inhibitor of beta-alanine oxidation, allowed the basolateral beta-alanine accumulation (measured in teased tubules) and the beta-alanine intracellular concentration (measured in primary cultures) to be similar to that for taurine. However the addition of AOA did not promote the net secretion of beta-alanine (measured as unidirectional fluxes in the cultured epithelium mounted in an Ussing chamber). The organic anions bromcresol green (BCG) (0.1 mM) and probenecid (1 mM) inhibited the net secretion of taurine by affecting the luminal efflux step. This suggests that a BCG- and probenecid-sensitive carrier in the luminal membrane facilitates the cell-to-lumen efflux of taurine and thus achieves net secretion.

Aminooxyacetic Acid↗
PubMed1993

Intracellular compartmentation of organic anions within renal cells.

Epifluorescence microscopy and video-image analysis were used to measure the distribution of the monovalent organic anion fluorescein (FL) within the cells of three organic anion-secreting renal epithelia: crab urinary bladder (a proximal tubule analogue), opossum kidney (OK) cells in culture, and intact teleost proximal tubules. In all three preparations the intracellular FL distribution was nonuniform. Two distinct intracellular compartments were detected, one being diffuse and cytoplasmic and the other punctate. With low FL concentrations in the medium (1 microM and below) dye accumulation in the punctate compartment exceeded that of the cytoplasm. In crab bladder epithelium FL uptake into both compartments was inhibited by external probenecid, p-aminohippurate (PAH), and LiCl and stimulated by 10-50 microM external glutarate, suggesting that the punctate compartment loaded by a two-step mechanism: transport into the cytoplasm at the basolateral membrane, followed by accumulation at specific intracellular sites. Experiments in which FL was microinjected into OK cells directly demonstrated movement of FL from the cytoplasmic to the punctate compartment. Accumulation in the latter was specific, i.e., inhibitable by coinjected PAH and probenecid, and energy dependent. Together, these findings indicate that during secretion organic anions are sequestered within renal cells. The role of sequestration in overall transport remains to be determined.

Animals↗
PubMed1980

Effect of DIDS on renal tubular transport.

Two stilbene derivates that had been used to covalently label the Cl- carrier in the erythrocyte were investigated for reactivity with the renal organic anion system. These compounds, 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS) and (4,4'-diisothiocyano)-dihydrostilbene-2,2'-disulfonate (H2DIDS), were found to be potent inhibitors (Ki congruent to 35 microM) of p-aminohippurate (PAH) transport in the renal cortical slice without affecting tetraethylammonium (TEA) transport or tissue viability. During renal clearance studies performed in the perfused kidney, DIDS decreased the PAH/inulin clearance ratio to congruent to 1. When the possible renal transport of [3H]H2DIDS was investigated, the renal slice transport or binding of [3H]H2DIDS reached a slice-to-medium ratio of congruent to 6, and this accumulation was decreased by probenecid. In perfused kidney experiments, the [3H]H2DIDS/inulin clearance ratio was congruent to 0.8. Since probenecid reduced this clearance ratio to congruent to 0.5, there was the possibility that H2DIDS underwent tubular secretion. In conclusion, DIDS and H2DIDS interacted with the renal organic anion transport system, which indicated that these compounds were possible probes for this transport system.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1991

Indirect Na+ dependency of urate and p-aminohippurate transport in pig basolateral membrane vesicles.

Membrane vesicles were used to study the basolateral transport of urate and p-aminohippurate (PAH) in the proximal tubule of the pig kidney. Consistent with a cooperation between a Na(+)-2-oxoglutarate cotransporter and a 2-oxoglutarate-urate or a 2-oxoglutarate-PAH exchanger, urate and PAH uptakes were stimulated in presence of extravesicular 2-oxoglutarate when an inwardly directed Na+ gradient was applied. Both transports exhibited, however, different characteristics. The optimal 2-oxoglutarate concentration for stimulating uptakes was 10 microM for PAH and 150 microM for urate. Extravesicular chloride was required to observe a stimulation of PAH uptake but not of urate uptake. Transports of both PAH and urate exhibited different affinity sequences for various organic anions. Stimulated PAH uptake was inhibited by probenecid greater than cold PAH greater than urate = pyrazinoate greater than lactate, whereas stimulated urate uptake was inhibited by probenecid greater than cold urate greater than PAH and not by pyrazinoate or lactate. These results are consistent with independent transport processes for urate and PAH in pig basolateral membrane vesicles, both being indirectly driven by an inwardly directed Na+ gradient.

Animals↗
PubMed1996

Fluorescence imaging study of organic anion transport from renal proximal tubule cell to lumen.

The mechanisms driving organic anion transport from cell to lumen were studied in intact killifish proximal tubules using fluorescence microscopy. Three fluorescent substrates were used as follows: 1) fluorescein (FL); 2) carboxyfluorescein (CF), generated intracellularly from carboxyfluorescein diacetate (CFDA); and 3) bimane-S conjugates, generated intracellularly by conjugation of monochlorobimane (MCB) with glutathione (GSH) and subsequent metabolism. The latter two substrates bypassed the basolateral uptake mechanism, allowing direct study of luminal transport mechanisms. At steady state, for all three substrates, luminal fluorescence was two to three times higher than cellular fluorescence. With FL as substrate, addition of p-aminohippurate (PAH) or probenecid to the incubation medium reduced cellular and luminal fluorescence to roughly the same extent. With CFDA or MCB as substrate, PAH and probenecid only slightly reduced cellular fluorescence but greatly reduced luminal fluorescence. MCB blocked transport of FL from cell to lumen; CFDA blocked transport of bimane-S conjugates from cell to lumen. Finally, depolarizing tubule cells with high-potassium medium did not affect the steady-state lumen-to-cell distribution of FL, CF, or bimane-S conjugates. These results show that organic anion transport from cell to lumen is mediated and uphill but not sensitive to the electrical potential difference across the luminal membrane.

Animals↗
PubMed2005

The multidrug resistance protein 5 (ABCC5) confers resistance to 5-fluorouracil and transports its monophosphorylated metabolites.

5'-Fluorouracil (5-FU), used in the treatment of colon and breast cancers, is converted intracellularly to 5'-fluoro-2'-deoxyuridine (5-FUdR) by thymidine phosphorylase and is subsequently phosphorylated by thymidine kinase to 5'-fluoro-2'-dUMP (5-FdUMP). This active metabolite, along with the reduced folate cofactor, 5,10-methylenetetrahydrofolate, forms a stable inhibitory complex with thymidylate synthase that blocks cellular growth. The present study shows that the ATP-dependent multidrug resistance protein-5 (MRP5, ABCC5) confers resistance to 5-FU by transporting the monophosphate metabolites. MRP5- and vector-transfected human embryonic kidney (HEK) cells were employed in these studies. In 3-day cytotoxicity assays, MRP5-transfected cells were approximately 9-fold resistant to 5-FU and 6-thioguanine. Studies with inside-out membrane vesicles prepared from transfected cells showed that MRP5 mediates ATP-dependent transport of 5 micromol/L [(3)H]5-FdUMP, [(3)H]5-FUMP, [(3)H]dUMP, and not [(3)H]5-FUdR, or [(3)H]5-FU. The ATP-dependent transport of 5-FdUMP showed saturation with increasing concentrations and had a K(m) of 1.1 mmol/L and V(max) of 439 pmol/min/mg protein. Uptake of 250 micromol/L 5-FdUMP was inhibited by dUMP, cyclic nucleotide, cyclic guanosine 3',5'-monophosphate, amphiphilic anions such as probenecid, MK571, the phosphodiesterase inhibitors, trequinsin, zaprinast, and sildenafil, and by the chloride channel blockers, 5-nitro-2-(3-phenylpropylamino)-benzoic acid and glybenclamide. Furthermore, the 5-FU drug sensitivity of HEK-MRP5 cells was partially modulated to that of the HEK-vector by the presence of 40 micromol/L 5-nitro-2-(3-phenylpropylamino)-benzoic acid but not by 2 mmol/L probenecid. Thus, MRP5 transports the monophosphorylated metabolite of this nucleoside and when MRP5 is overexpressed in colorectal and breast tumors, it may contribute to 5-FU drug resistance.

Adenosine Triphosphate↗
PubMed1992

Transport of cimetidine across the basolateral membrane of rabbit kidney proximal tubules: interaction with organic anions.

Since in whole animal studies and in man the renal clearance of cimetidine was prolonged by the coadministration of probenecid, the aim of the present study was to examine the interaction of the organic base cimetidine with the organic anion transport system at the basolateral membrane of isolated non-perfused rabbit proximal tubules. S2 segments of proximal tubules were incubated at 37.5 degrees C with 3H-cimetidine (2 x 10(-7) mol/l) or 3H-PAH (4 x 10(-6) mol/l, as a marker for the organic anion transport system) and 14C-inulin (marker for the extracellular space) for 25 min to achieve a steady state. Afterwards, a nonradiolabelled substance was added to the bath, and the change of the cellularly stored radioactivity was measured at 5-min intervals. Probenecid (5 x 10(-5) mol/l) decreased the cellular amount of 3H-cimetidine to 26% of the control value. At this concentration, furosemide and Na2SO4 had no effect. At a concentration of 10(-3) mol/l, these substances reduced the cellular 3H-cimetidine uptake to 33% (furosemide) and 57% (Na2SO4) of the control value. 10(-4) and 10(-3) mol/l succinate diminished the steady-state uptake of cimetidine to 77% and 53% of the control value, respectively. On the other hand, cimetidine (10(-3) mol/l) decreased the cellular uptake of 3H-PAH to 52% of the control value. N1-methylnicotinamide (5 x 10(-5) mol/l and 10(-3)mol/l) had no effect on the steady-state uptake of 3H-PAH. These results indicate that the organic base cimetidine, besides its high affinity for the cation transporter, also interacts with the organic anion transport system at the basolateral membrane of rabbit proximal tubules.

Algorithms↗
PubMedDate not supplied

Cisplatin nephrotoxicity: site of functional disturbance and correlation to loss of body weight.

We have investigated the effect of an intraperitoneal cisplatin injection (5 mg/kg body weight) into male Wistar rats on: (1) body weight; (2) proximal tubular transport of D-glucose and sulfate across the luminal membrane; (3) transport of p-aminohippuric acid (PAH) and sulfate across the contraluminal membrane; (4) urinary excretion of inulin; (5) urinary excretion and tissue accumulation of sulfofluorescein, and (6) effect of the 'protecting substances', N-Methyl-D-glucamine-dithiocarbamate (NaG), diethyldithiocarbamate, mercaptosuccinate (MS), probenecid, and glycine on parameters 1, 4 and 5. Five days after intraperitoneal application of cisplatin the following effects were observed: (1) body weight was reduced on average by 11% as compared to a 12% increase in control animals; (2) luminal sulfate and D-glucose transport was inhibited correlating with the degree of weight loss; (3) contraluminal PAH transport was also decreased in correlation to the loss of body weight, while contraluminal sulfate transport was not inhibited by cisplatin; (4) inulin excretion was reduced by 45%, the pattern for protection was the same as for the prevention of weight loss; (5) sulfofluorescein (SF) excretion in the urine was reduced by 43%, and (6) accumulation of SF into cortical tissue was augmented. Protecting substances prevented or mitigated weight loss, fall of urinary inulin and SF excretion as well as SF accumulation in cortical tissue with a similar pattern: N-glucamine-dithiocarbamate > mercaptosuccinate approximately probenecid approximately glycine. The data indicate: (1) that luminal (glucose and sulfate) and contraluminal (PAH) transport processes are affected by cisplatin; (2) that contraluminal transport (sulfate) can be unaffected or less affected than luminal transport processes (SF); (3) our method (SF) gives the possibility to monitor the balance between luminal and contraluminal transport steps in vivo; and (4) the correlation of body weight loss with decay of certain renal transport functions and their prevention with similar protecting patterns indicates that a simple index might be useful to monitor the cytotoxic status of an individual.

Animals↗