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At least 1,117 records · Page 62Linked to original sources
PubMed2004

Simultaneous expression of guinea pig UDP-glucuronosyltransferase 2B21 (UGT2B21) and 2B22 in COS-7 cells enhances UGT2B21-catalyzed chloramphenicol glucuronidation.

Our previous study suggested that hetero-oligomer formation of guinea pig liver UDP-glucuronosyltransferases (UGTs) 2B21 and 2B22 enhances UGT2B21-catalyzed morphine-6-glucuronidation. In this work, further evidence for a functional hetero-oligomer between UGT2B21 and UGT2B22 was provided by studies of the glucuronidation of chloramphenicol with dual expression in COS-7 cells. UGT2B21 expressed in COS cells was capable of glucuronidating the 3-hydroxyl group of morphine, 4-hydroxybiphenyl, borneol, testosterone, androsterone, and estriol, whereas it had some effect on chloramphenicol. On the contrary, UGT2B22 does not exhibit any significant activity toward these typical substrates tested in this study. When UGT2B21 and UGT2B22 were expressed simultaneously, the chloramphenicol glucuronidation was enhanced to 4.5-fold, whereas the activities toward other substrates were little affected except that for the 6-hydroxyl group of morphine. The protein expression level of UGT2B21 was comparable when UGT2B21 was expressed with or without UGT2B22. These results suggest that simultaneous expression of UGT2B21 and UGT2B22 enhances UGT2B21-catalyzed chloramphenicol glucuronidation. Hetero-oligomer formation of UGT2B21 and UGT2B22 may act by fine-tuning the catalytic glucuronidation of chloramphenicol.

Animals↗
PubMed2003

Human renal organic anion transporter 1-dependent uptake and toxicity of mercuric-thiol conjugates in Madin-Darby canine kidney cells.

Mercuric ions are highly reactive and form a variety of organic complexes or conjugates in vivo. The renal proximal tubule is a primary target for mercury uptake and toxicity, and circumstantial evidence implicates organic anion transporters in these processes. To test this hypothesis directly, the transport and toxicity of mercuric-thiol conjugates were characterized in a Madin-Darby canine kidney cell line stably transfected with the human organic anion transporter 1 (hOAT1). 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-terazolium bromide assays (for mitochondrial dehydrogenase) confirmed that mercuric conjugates of the thiols N-acetylcysteine (NAC), cysteine, or glutathione were more toxic in hOAT1-transfected cells than in the nontransfected cells. The NAC-Hg(2+) conjugate was most cytotoxic, inducing greater than 50% cellular death over 18 h at a concentration of 100 microM. The cytotoxic effects were fully reversed by probenecid (an OAT1 inhibitor) and partially reversed by p-aminohippurate (an OAT1 substrate). Toxicity of this conjugate was reduced by the OAT1-exchangeable dicarboxylates alpha-ketoglutarate, glutarate, and adipate, but not by succinate, a nonexchangeable dicarboxylate. (203)Hg-uptake studies showed probenecid-sensitive uptake of mercury-thiol conjugates in the hOAT1-transfected cells. The apparent K(m) for the NAC-Hg(2+) conjugate was 44 +/- 9 microM. Uptake of the NAC-Hg(2+) conjugate was cis-inhibited by glutarate, but not by methylsuccinate, paralleling their effects on toxicity. Probenecid-sensitive transport of the NAC-Hg(2+) conjugate was also shown to occur in Xenopus laevis oocytes expressing the hOAT1 or the rOAT3 transporters, suggesting that OAT3 may also transport thiol-Hg(2+) conjugates. Thus, renal accumulation and toxicity of thiol-Hg(2+) conjugates may depend in part on the activity of the organic transport system.

Animals↗
PubMed1995

Anticytomegaloviral activity and safety of cidofovir in patients with human immunodeficiency virus infection and cytomegalovirus viruria.

Cidofovir (HPMPC; (S)-1-[3-hydroxy-2-(phosphonylmethoxy)propyl]cytosine) is a nucleotide analog with activity against human cytomegalovirus (CMV). A phase I/II dose escalation trial was conducted with asymptomatic human immunodeficiency virus (HIV)-infected patients with CMV viruria to determine its pharmacokinetics, maximally tolerated dose, and preliminary antiviral activity against CMV. Qualitative CMV blood and urine cultures were monitored weekly to assess anti-CMV activity. Twenty-one HIV-infected persons with CD4 counts from 0 to 389 cells per microliters (median, 39) were enrolled in six dose-ranging groups. The first five groups enrolled four patients each to receive cidofovir infusions either weekly or biweekly for 4 weeks or every 3 weeks for 12 weeks. The sixth group enrolled one patient who received infusions of 5 mg/kg of body weight every other week. Patients receiving 0.5 or 1.5 mg/kg twice weekly experienced no serious toxicity. The first two patients who received 5 mg/kg twice weekly developed glycosuria and 2+ proteinuria. Subsequent patients received concomitant probenecid to attempt to ameliorate renal toxicity. Seventeen patients experienced proteinuria on one or more occasions; 6 of them experienced at least 2+ proteinuria. Four patients did not complete the study as planned because of renal toxicity. Positive CMV urine cultures reverted to negative in 2 of 8 patients receiving doses of < or = 1.5 mg/kg twice weekly and 11 of 13 patients receiving higher doses. Cidofovir has in vivo anti-CMV activity demonstrated by prolonged clearing of CMV viruria, although this observation is tempered by the fact that clearance of viremia could not be demonstrated. The dose-limiting toxicity is renal; however, concurrent administration of probenecid may be protective. The maximally tolerated weekly intravenous dose with probenecid is approximately 5 mg/kg. Efficacy trials with CMV disease will define the therapeutic utility and optimal dosing interval for cidofovir.

Adult↗
PubMed2002

Involvement of multidrug resistance-associated protein 2 in intestinal secretion of grepafloxacin in rats.

We investigated the contribution of multidrug resistance-associated protein 2 (MRP2) to the secretory transport of grepafloxacin and compared its functional role with that of P-glycoprotein (P-gp) by using Sprague-Dawley rats (SDRs) and Eisai hyperbilirubinemic rats (EHBRs), in which MRP2 is hereditarily defective. In intestinal tissue from SDRs mounted in Ussing chambers, the level of transport in the direction from the serosal layer to the mucosal layer was twofold greater than that in the direction from the mucosal layer to the serosal layer. This secretory transport of grepafloxacin was diminished by both probenecid, an MRP2 inhibitor, and cyclosporine, a P-gp inhibitor. In intestinal tissue from EHBRs, the secretory transport of grepafloxacin was lower than that in intestinal tissue from SDRs and was inhibited by cyclosporine but not by probenecid. The absorption of grepafloxacin from intestinal loops in SDRs was in the order of duodenum > jejunum > ileum and was increased by cyclosporine but not by probenecid. The absorption in EHBRs was not higher than that in SDRs. The intestinal secretory clearance in SDRs after intravenous administration of grepafloxacin was shown to be greater for the ileum than for the duodenum, which is in good agreement with the previously reported regional expression profile of MRP2 mRNA. The intestinal secretory clearance was lower in EHBRs than in SDRs. Accordingly, in addition to P-gp, MRP2 might play a role in the secretory transport of grepafloxacin. The function of MRP2 in facilitating grepafloxacin transport in the secretory direction is more pronounced both in vitro and in vivo, while the restriction of entry from the lumen into the cell by MRP2 seems to be negligible, compared with that by P-gp, in the case of grepafloxacin.

Animals↗
PubMed1976

Single oral dose of 1-5g. talampicillin in the treatment of gonorrhoea.

81 patients have been treated with single oral doses of 1-5 g. (6 tablets) of talampicillin without probenecid. The failure rate amongst those followed was only 4-2 per cent. No side-effects were reported. These results were superior to those obtained with 2-0g. or equivalent of ampicillin, amoxycillin, or pivampicillin with probenecid. Talampicillin is thus the most potent ampicillin-like antibiotic so far available for the treatment of gonorrhoea and is capable of curing the disease with a smaller single dose without probenecid than is necessary for other preparations.

Administration, Oral↗
PubMed1977

Long-term treatment of juvenile Huntington's chorea with dipropylacetic acid.

Since the proposed mode of action of dipropylacetic acid, an anticonvulsant, is to increase central nervous system gamma-aminobutyric acid levels, we used this agent to treat identical twins with juvenile Huntington's chorea. Their clinical status did not improve immediately after they received dipropylacetic acid. Furthermore, long-term administration (over a year) of high doses of the agent (up to 2,400 mg per day; 92 mg per kilogram per day) did not seem to alter the slow progression of their disease. Prior to treatment with dipropylacetic acid, the twins had normal cerebrospinal fluid gamma-aminobutyric acid levels. In addition, cerebrospinal fluid 5-hydroxyindoleacetic acid and homovanillic acid were determined before and after 18 hours of high-dose probenecid. The former showed a normal threefold to fourfold increase after probenecid administration, but homovanillic acid had a distinctly subnormal turnover after probenecid, with only a threefold rather than the normal tenfold increase.

Child↗
PubMed1993

Pharmacokinetic drug interactions with ACE inhibitors.

Angiotensin converting enzyme (ACE) inhibitors which have active moieties excreted mainly in urine require adjustment of either the dose or the interval between doses in patients with moderate to severe renal dysfunction or severe congestive heart failure. Those agents such as temocapril (CS 622) and fosinopril, excreted both in urine and bile, may not require such adjustment. Renal clearance of ACE inhibitors may be reduced and some accumulation may occur in elderly patients with mild renal dysfunction or congestive heart failure. The bioavailability of ACE inhibitors is reduced by concomitant food or antacids which may slow gastric emptying and raise gastric pH. Pharmacokinetic interactions with ACE inhibitors are unlikely in patients receiving thiazide or loop diuretics. When ACE inhibitors are given hyperkalaemia may occur in patients with renal insufficiency, those taking potassium supplements or potassium-sparing diuretics, and in diabetic patients with mild renal impairment. While no pharmacokinetic interaction precludes use of this combination, the pharmacokinetics of some ACE inhibitors are subject to greater variability when patients also receive beta-blockers. Calcium antagonists and ACE inhibitors have additive anti-hypertensive effects and pharmacokinetic interactions between these agents are unlikely. One report exists of a significant effect of coadministered hydralazine on the pharmacokinetics and urinary excretion of lisinopril. Data on interactions between ACE inhibitors and digitalis are contradictory. There is no evidence that the concomitant use of ACE inhibitors and digoxin is associated with an increased risk of digitalis toxicity. ACE inhibitors are mainly excreted by glomerular filtration and renal tubular secretion. Possible interactions between ACE inhibitors and probenecid have been noted, with renal and total body clearance of ACE inhibitors being potentially reduced in the presence of probenecid. Probenecid pretreatment may enhance the pharmacodynamic response of ACE inhibitors. Few but contradictory data exist on the effects of H2-blockers on ACE inhibitor pharmacokinetics and little information is available on interactions between ACE inhibitors and hypoglycaemic drugs. Some case reports link ACE inhibitors with the induction of lithium toxicity. Coadministration of lithium should be undertaken with caution, and frequent monitoring of lithium concentrations is recommended with all ACE inhibitors. Nonsteroidal anti-inflammatory drugs (NSAIDs) may attenuate the haemodynamic actions of ACE inhibitors. NSAIDs reduce renal excretion of ACE inhibitors, with a corresponding increase in circulating drug concentrations. There is little information available on the pharmacokinetic interaction with ACE inhibitors and cyclosporin, but caution should be employed when they are used together.(ABSTRACT TRUNCATED AT 400 WORDS)

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1993

[Some effects of pH, diuretics and organic acids on the uptake of oxalate in a renal tubular cell line (LLC-PK1)].

The effects of changes in extracellular pH and treatments with diuretics or some organic acids on the uptake of oxalate were studied in an epithelial cell line of renal origin (LLC-PK1 cells). The oxalate uptake into the cells exhibited a marked sensitivity to extracellular, pH, in the present results with acidic pH stimulating and alkaline pH inhibiting the DIDS sensitive uptakes. The uptake of oxalate was clearly inhibited by DIDS, proportionally to the concentrations from 10 microM to 1 mM. Furosemide, chlorothiazide, probenecid and acetazolamide inhibited the oxalate uptake significantly. Probenecid has the most potency on the inhibition of the uptake in high concentrations, and acetazolamide needed a high concentration for the small effect. However, allopurinol has no effect on the uptake as well as dicarboxylates (malate, succinate and phenyl succinate) and organic acids (urate and para-amino hippurate). We discussed the mechanisms of the inhibition against the oxalate uptake concerning with each drug. It was suggested that probenecid may inhibit the oxalate carriers directly, while furosemide, chlorothiazide and acetazolamide may inhibit then by the direct actions and some secondary effects which are provided by those drugs.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1997

Intravenous cidofovir for peripheral cytomegalovirus retinitis in patients with AIDS. A randomized, controlled trial.

BACKGROUND: Cytomegalovirus (CMV) retinitis is the most common intraocular infection in patients with the acquired immunodeficiency syndrome (AIDS). If left untreated, it may lead to progressive destruction of retinal tissue and blindness. Cidofovir is a nucleotide analogue of cytosine that has potent, prolonged in vitro and in vivo activity against herpesviruses, including many CMV isolates that are resistant to ganciclovir and foscarnet. OBJECTIVE: To determine whether intravenous cidofovir delays progression of previously untreated CMV retinitis. DESIGN: Randomized, controlled trial comparing immediate with deferred cidofovir treatment. Patients in the deferred treatment group were eligible to receive cidofovir after progression of CMV retinitis was documented by retinal photography. SETTING: Eight academic medical centers and an independent center that read retinal photographs. PATIENTS: 48 patients with AIDS and previously untreated peripheral CMV retinitis who were randomly assigned to immediate (n = 25) or deferred treatment (n = 23). INTERVENTION: Intravenous cidofovir, 5 mg/kg of body weight, once weekly for 2 weeks and then once every other week. To minimize nephrotoxicity, oral probenecid and intravenous hydration with normal saline were administered with each cidofovir infusion. MEASUREMENTS: Progression of CMV retinitis was assessed by bilateral, full-field retinal photographs that were read by an ophthalmologist who was masked to treatment assignment. Incidence of side effects, changes in visual acuity, effect on CMV shedding in urine and blood, and mortality were also assessed. RESULTS: The median time to progression of CMV retinitis was 22 days (95% CI, 10 to 27 days) in the deferred treatment group and 120 days (CI, 40 to 134 days) in the immediate treatment group (P < 0.001). Neutropenia (15%) and proteinuria (12%), both asymptomatic, were the most common serious adverse events considered to be possibly related to cidofovir. Cidofovir treatment was discontinued in 10 of 41 patients (24%) because of protocol-defined treatment-limiting nephrotoxicity. Transient reactions to probenecid, including mild to moderate constitutional symptoms or nausea, occurred in 23 of 41 patients (56%) and were dose limiting in 3 (7%). CONCLUSIONS: Cidofovir was efficacious in delaying progression of previously untreated CMV retinitis. Treatment was associated with manageable side effects; strict adherence to monitoring of renal function before cidofovir was administered and concomitant administration of probenecid and saline hydration appeared to minimize drug-related nephrotoxicity.

AIDS-Related Opportunistic Infections↗
PubMed1976

Drug treatment of venereal disease: analysis of 273 cases in Ghana.

The presence of non-gonococcal urethritis, resistant to penicillin therapy was noted by Ikejiani in Nigeria as early as 1955. This syndrome is now known as non-specific urethritis, or non-specific genital infection in the female. Sarrat (1973) has shown the effectiveness of penicillin plus probenecid, specti nomycin, and cotrimoxazole in male cases of gonorrhoea in Dakar. Sogbetun and Osoba (1974) have shown the effectiveness of metronidazole in trichomoniasis in males in Nigeria. Our study was made on a mixed University population of 2,700 students seen in one clinic during the year 1975. There were 273 cases of sexually transmitted diseases including gonorrhoea, non-specific urethritis or genital disease, trichomoniasis and chronic urethritis or vaginitis. Treatment of gonorrhoea with penicillin alone or with spectinomycin was only 50% effective. But good results were obtained with penicillin plus probenecid or penicillin plus cotrimoxazole. Good results were obtained in non-specific urethritis, or non-specific genital disease, when tetracycline or its derivatives were used. Good results were obtained in the treatment of trichomoniasis with metronidazole in males and females. It was concluded that in gonorrhoea penicillin should be given (in adequate dosage) with probenecid or cotrimoxazole. Spectinomycin should be used at a dose level of 4 g instead of 2 g. The management of chronic urethritis and vaginitis was very difficult. The drug treatment of venereal disease in Ghana has not revealed any unique characteristics except, perhaps, an increased resistance of the gonococcus to spectinomycin.

Female↗
PubMed1987

Methotrexate efflux in L1210 cells. Kinetic and specificity properties of the efflux system sensitive to bromosulfophthalein and its possible identity with a system which mediates the efflux of 3',5'-cyclic AMP.

Methotrexate exits L1210 mouse leukemia cells via multiple routes that include a unidirectional efflux component which is sensitive to bromosulfophthalein. This efflux component has been characterized in the present study after eliminating the contribution from the other efflux routes by treatment of the cells with an active ester of methotrexate and by reducing the assay pH to 6.2. The remaining efflux at pH 6.2 was greater than 90% sensitive to bromosulfophthalein. This route was also inhibited by probenecid, prostaglandin A1, diamide, 1-methyl-3-isobutylxanthine, various metabolic inhibitors, and by transfer of the cells to a buffer containing high concentrations of KCl. The inhibition by prostaglandin A1 was exceptionally potent and reached 50% at a concentration of 0.5 microM. An enhancement in efflux occurred upon the addition of glucose or by transfer of the cells to a non-saline buffer. When parameters relating to cellular energetics were measured, a reduction in ATP level was associated with the inhibition of efflux by probenecid, carbonylcyanide m-chlorophenylhydrazone, valinomycin, and antimycin A, whereas the increase in efflux by glucose was accompanied by an increase in intracellular ATP. Changes in ATP, however, were not associated with the inhibition by various other compounds or additions or with the enhancement in efflux by the non-anionic buffer. When the relative sensitivity of methotrexate efflux to bromosulfophthalein, 4,4'-diisothiocyanostilbene-2,2'-disulfonate, and lactic anhydride was compared with other anion transport systems, differences in specificity indicated that methotrexate was not exiting the cells via the bicarbonate/chloride exchange carrier, the lactate/H+ co-transport system, or a system which mediates the efflux of phthalate. However, a correlation was apparent between the sensitivity of methotrexate efflux to inhibition by prostaglandin A1, probenecid, and certain metabolic inhibitors and the ability of these same compounds to inhibit the unidirectional efflux of 3',5'-cyclic AMP in other cell lines, suggesting that methotrexate may share a common efflux route with cyclic nucleotides.

Adenosine Triphosphate↗
PubMed1988

Pharmacokinetics and bioavailability of ceftriaxone administered intravenously and intramuscularly to calves.

Ceftriaxone was administered to Israeli-Friesian male calves by IV and IM routes. The antibiotic was administered IV (10 mg/kg) to 10 calves and IM to 23 calves; 8 were given the antibiotic at the rate of 10 mg/kg of body weight, 5 were given 20 mg/kg, and 10 were given 10 mg/kg, together with probenecid at 40 mg/kg. Serum concentration vs time profiles measured after IV and IM administration were analyzed by use of statistical moment theory. The following mean values +/- SD were found: elimination half-life (t1/2) was 83.8 +/- 8.6 minutes after IV administration and significantly longer 116.8 +/- 20.5 minutes (P less than 0.001) after IM administration at 10 mg/kg. The t1/2 was increased to 141.3 +/- 24.4 minutes by the coadministration of probenecid and to 145.0 +/- 48.2 minutes by doubling the IM dosage to 20 mg/kg. The total body clearance was 3.39 +/- 0.42 ml/min/kg and the renal clearance 2.37 +/- 0.74 ml/min/kg. The specific volume of distribution was 0.2990 +/- 0.0510 L/kg. The average mean residence time (MRT) was 94.0 +/- 12.3 minutes after IV administration and 137.6 +/- 19.9 minutes after IM administration of ceftriaxone at 10 mg/kg. The MRT was increased to 198 +/- 48.8 minutes by the coadministration of probenecid and to 191.0 +/- 59.4 minutes by doubling the IM dose. The former value was significantly different from the MRT after IM administration of the antibiotic at 10 mg/kg. Bioavailability of ceftriaxone after IM administration at 10 mg/kg and at 20 mg/kg was 78% and 83%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Carrier-mediated transport of cefixime, a new cephalosporin antibiotic, via an organic anion transport system in the rat renal brush-border membrane.

The renal excretion mechanism of cefixime, a newly developed and p.o. effective cephalosporin antibiotic, was investigated by using the renal brush-border membrane vesicles from the rat kidney cortex. The initial uptake rate of cefixime into an osmotically sensitive vesicular space showed concentration and temperature dependencies, indicating the presence of a carrier-mediated transport mechanism for cefixime. Kinetic parameters for apparently saturable and nonsaturable components were evaluated as follows: maximum uptake rate was 7.32 +/- 1.07 nmol/30 sec/mg of protein; Michaelis constant was 7.35 +/- 2.04 mM; and the first-order rate constant was 0.34 +/- 0.02 nmol/30 sec/mg of protein per mM. The uptake was not affected by an inward-directed gradient of Na+, K+, Li+, Rb+ or H+. In contrast, the initial uptake rate was enhanced by an inside-positive membrane potential imposed by valinomycin. Although amino acids, dipeptides and organic cations had no effects on the uptake of cefixime, organic anions such as probenecid and p-aminohippuric acid and anion transport inhibitors such as 4,4'-diisothiocyano-stilbene-2,2'-disulfonic acid and furosemide reduced the uptake significantly. Twenty beta-lactam antibiotics including both zwitter-ionic and anionic derivatives inhibited significantly the uptake of cefixime. Furthermore, by adding probenecid in the extravesicular medium, an efflux of cefixime from the brush-border membrane vesicles was enhanced significantly at the initial stage. Benzylpenicillin, cephalothin and cephradine also enhanced an efflux of cefixime to the same extent as observed by the addition of probenecid.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Renal transport and renal metabolism of 2, 4, 5-trichlorophenoxyacetate by the chicken.

In vitro and in vivo renal tubular transport of 2,4,5-trichlorophenoxyacetate (2,4,5-T), a hormone-type herbicide, was studied in the chicken. Renal cortical slices incubated with 14C-labeled 2,4,5-T demonstrated a slice-to-medium ratio of the 14C-label of 26 after 2 hr of incubation. This accumulation was inhibited significantly by probenecid, phenol red, dinitrophenol and iodoacetamide. In vitro metabolism of 2,4,5-T was apparent in the renal slice studies; at least two metabolites were found by electrophoretic analysis. Even though chicken liver slices were able to accumulate 2,4,5-T, the accumulated herbicide was not metabolized. In addition, chicken kidney slices metabolized 2,4,5-T to a much greater extent than did rat or rabbit kidney slices, which produced only negligible amounts of metabolites. When [14C]-2,4,5-T was infused into the renal portal system of the chicken, the 14C-label originally associated with 2,4,5-T was shown to be secreted by the renal tubule. Probenecid inhibited the transport of the 14C-label without affecting the simultaneous transport of tetra-ethylammonium, an organic cation transported by the renal proximal tubule. At the present infusion rate of 2,4,5-T (2.9 X 10(-10) mol/min), the excreted label was associated primarily with an acidic metabolite(s). It can be concluded that the chicken transports 2,4,5-T by a probenecid sensitive mechanism; however, this transport appears to be associated with the metabolism of the herbicide.

2,4,5-Trichlorophenoxyacetic Acid↗
PubMed1993

Lactate transport in macrophages.

Macrophages perform phagocytic and effector activities in a number of different tissues. The environment of the inflammatory foci in which they function is often acidic and contains an abundance of lactate. We characterized the ability of thioglycollate-elicited mouse peritoneal macrophages to accumulate lactate from the medium and to use this lactate to maintain intracellular energy stores. Lactate uptake was stereospecific for L-lactate and was inhibited by the organic anion transport blocker probenecid but not by concentrations of 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid that block anion exchangers. L-[14C]Lactate uptake was not affected by variation of the extracellular Na+ concentration but was enhanced by acidification of the extracellular medium, suggesting that lactate uptake was mediated by a proton cotransport system. The enhanced accumulation of [14C]-lactate seen in medium at pH 6.0 to 6.5 was inhibited by probenecid or by an excess of unlabeled L-lactate. When macrophages were incubated in PBS without glucose for 6 h, intracellular stores of phosphocreatine were 13 nmol/mg of protein, compared with 44 nmol/mg of protein in cells incubated in medium containing glucose. When lactate was substituted for glucose, phosphocreatine stores were 32 nmol/mg of protein. These studies reveal that macrophages take up L-lactate in a pH-dependent manner and that lactate uptake occurs via a probenecid-inhibitable monocarboxylate transporter; they suggest that macrophages can utilize this lactate as an energy source.

Adenosine Triphosphate↗
PubMed1993

Movement of fluorescein and its glucuronide across retinal pigment epithelium-choroid.

PURPOSE: To characterize movement of fluorescein and its glucuronide across the blood-retinal barrier. METHODS: Retinal pigment epithelium (RPE)-choroid preparations from New Zealand albino rabbit were sealed in an Ussing-type chamber in a stabilized condition for 3 hr, where movement of fluorescein and fluorescein glucuronide across the RPE-choroid was studied under a short circuit condition. RESULTS: The outward (vitreous-choroid) permeability to fluorescein determined at a concentration of 15 mumol/l was about 4 times greater than the inward (choroid-vitreous) permeability (P < 0.01). The outward permeability was significantly decreased by 50-65% by metabolic or competitive inhibitors (1 mumol/l ouabain, 10 mumol/l 2,4-dinitrophenol, 100 mumol/l probenecid, 30 mmol/l hippurate, or 5 mmol/l iodipamide), whereas the inward permeability was not affected by any of the above competitive inhibitors. As the fluorescein concentration was increased from 15 to 150 mumol/l, the net fluorescein movement across the tissue indicated saturation, and a Lineweaver-Burk plot gave an apparent Km of 26 mumol/l and Vmax of 1.56 nmol/hr/cm2. The outward permeability to fluorescein glucuronide determined at 15 mumol/l was about double the inward permeability (P < 0.01) and about 1/3 of the outward permeability to fluorescein (P < 0.01). The outward permeability to fluorescein glucuronide was significantly decreased by about 50% by 1 mumol/l ouabain, 10 mumol/l 2,4-dinitrophenol, or 100 mumol/l probenecid, whereas the inward permeability was not affected by 100 mumol/l probenecid. CONCLUSION: These results suggest that the majority of the outward fluorescein movement across the tissue and part of that of fluorescein glucuronide depends on an active transport mechanism, whereas the inward movement of both fluorescein and fluorescein glucuronide occurs by a passive mechanism.

2,4-Dinitrophenol↗
PubMed1998

Glutathione-dependent biotransformation of the alkylating drug thiotepa and transport of its metabolite monoglutathionylthiotepa in human MCF-7 breast cancer cells.

In this study, the role of glutathione S-transferase (GST) P1-1, the cellular reduced glutathione (GSH) status, and ATP-dependent efflux pumps in the cellular glutathione-dependent biotransformation of thiotepa and transport of the main metabolite monoglutathionylthiotepa in relation to cytotoxicity was studied in control and GST-P1-1-transfected MCF-7 cell lines. It was demonstrated that an enhanced cellular level of GST-P1-1 leads to an enhanced formation of monoglutathionylthiotepa, which is transported out of the cell into the medium. Monoglutathionylthiotepa was able to reversibly inhibit the activity of purified GST-P1-1, but only at nonphysiological concentrations, indicating that feedback inhibition of GST by its metabolites is not a relevant process in vivo. The GST activity, cellular GSH level, and/or ATP-dependent efflux of monoglutathionylthiotepa were modulated using ethacrynic acid, D,L-buthionine-S,R-sulfoximine, probenecid, and verapamil to understand the interplay between GSTs, glutathione conjugation, and efflux of glutathione conjugates in more detail. Inhibition of the GSH biosynthesis by D,L-buthionine-R,S-sulfoximine, a specific inhibitor of gamma-glutamylcysteine synthetase, significantly reduced the glutathione conjugation of thiotepa and potentiated the cytotoxicity of thiotepa. Pretreatment of cells with ethacrynic acid resulted in decreased formation of monoglutathionylthiotepa as a result of inhibition of GST in the GST-P1-1 transfectant. In addition, the intracellular amount of monoglutathionylthiotepa increased in both of the cell lines on exposure to ethacrynic acid, indicating that transport of the glutathione conjugate was partially inhibited by the glutathione conjugate of ethacrynic acid. Transport activity of monoglutathionylthiotepa could also be inhibited by probenecid and verapamil, inhibitors of organic anion transport, without influencing the biotransformation capacity of the cells. It was demonstrated that inhibition of glutathione conjugate efflux by probenecid and verapamil leads to enhanced cytotoxicity, which indicates that besides thiotepa, monoglutathionylthiotepa is also cytotoxic for the cells. Only enhanced biotransformation and subsequent transport of the glutathione conjugate into the medium (which occurs with the GST-P1-1 transfectant) results in enhanced viability. Therefore, it was concluded that only enhanced biotransformation of thiotepa represents a real detoxification pathway when the resulting conjugate is transported out of the cells. Altogether, the results indicate that it is not the overexpression of GST per se but the interplay between GSH/GST and glutathione conjugate efflux pumps that results in increased resistance to alkylating anticancer drugs such as thiotepa.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1977

Brain dopamine turnover and the relief of parkinsonism.

The relationship between dopamine receptor activation and the relief of parkinsonian clinical features was studied in 40 patients with Parkinson's disease. Treatment with dopamine receptor agonists, piribedil or bromocriptine, decreased significantly both the basal level and probenecid-induced accumulations of homovanillic acid (HVA) in the CSF. But there were no changes in the concentrations of 5-hydroxyindole acetic acid (5-HIAA). Correlation analyses showed that patients who improved with both the dopamine agonists used had significantly lower probenecid response of HVA in the CSF and a less severe disease condition than those without beneficial effect. This relationship between dopamine receptor activation and improvement of parkinsonian disability suggests that the therapeutic efficacy of dopamine receptor agonists depends on the functional capacity of brain dopaminergic mechanisms.

Brain↗