Antioxidant transport modulates peripheral airway reactivity and inflammation during ozone exposure.
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We examined the effects of ozone (O(3)) and endogenous antioxidant transport on canine peripheral airway function, central airway function, epithelial integrity, and inflammation. Dogs were either untreated or pretreated with probenecid (an anion-transport inhibitor) and exposed for 6 h to 0.2 parts/million O(3). Peripheral airway resistance (Rpa) and reactivity (DeltaRpa) were monitored in three sublobar locations before and after exposure to either air or O(3). Pulmonary resistance and transepithelial potential difference in trachea and bronchus were also recorded. Bronchoalveolar lavage fluid (BALF) was collected before, during, and after exposure. O(3) increased Rpa and DeltaRpa only in probenecid-treated dogs and in a location-dependent fashion. Pulmonary resistance and potential difference in bronchus increased after O(3) exposure regardless of treatment. O(3) markedly increased BALF neutrophils only in untreated dogs. With the exception of hexanal, O(3) did not alter any BALF constituent examined. Probenecid reduced BALF ascorbate, BALF protein, and plasma urate. We conclude that 1) a 6-h exposure to 0.2 parts/million O(3) represents a subthreshold stimulus in relation to its effects on peripheral airway function in dogs, 2) antioxidant transport contributes to the maintenance of normal airway tone and reactivity under conditions of oxidant stress, 3) O(3)-induced changes in Rpa and DeltaRpa are dependent on location, and 4) peripheral airway hyperreactivity and inflammation reflect independent responses to O(3) exposure. Finally, although anion transport mitigates the effect of O(3) on peripheral airway function, it contributes to the development of airway inflammation and may represent a possible target for anti-inflammatory prevention or therapy. (+info)
Role of organic anion transporter 1 (OAT1) in cephaloridine (CER)-induced nephrotoxicity.
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Role of organic anion transporter 1 (OAT1) in cephaloridine (CER)-induced nephrotoxicity. BACKGROUND: Cephaloridine (CER) has been used to elucidate the mechanisms of cephalosporin antibiotic-induced nephrotoxicity. Organic anion transporters have been thought to mediate CER uptake by the proximal tubule. The purpose of this study was to elucidate the possible involvement of organic anion transporter 1 (OAT1) in CER-induced nephrotoxicity. METHODS: A mouse terminal proximal straight tubule (S3) cell line stably expressing rat OAT1 (S3 rOAT1) was established and used in this study. The cellular uptake of [14C]-para-aminohippuric acid (PAH), a prototype organic anion, and that of [14C]-CER were measured. The effects of CER on the viability of the cells and the amount of lipid peroxidation were estimated. RESULTS: S3 rOAT1 expressed a functional organic anion transporter in the cytoplasmic membrane, and exhibited CER uptake activity. CER treatment resulted in a more significant decrease in the viability and a more significant increase in the amount of lipid peroxidation in S3 rOAT1 than in S3 cells transfected with an expression vector lacking the rOAT1 insert. Probenecid, an inhibitor of organic anion transport, and probucol, an antioxidant, significantly suppressed the decrease in viability and increase in the amount of lipid peroxidation in S3 rOAT1 treated with CER. The effects of various cephalosporin antibiotics on the uptake of [14C]PAH were correlated significantly with the effects of these drugs on cell viability. CONCLUSIONS: These results suggest that rOAT1 is, at least in part, responsible for the cellular uptake of CER and therefore CER-induced nephrotoxicity. (+info)
Effect of pyrazinamide and probenecid on peritoneal urate transport kinetics during continuous ambulatory peritoneal dialysis.
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OBJECTIVE: We administered pyrazinamide (PZA) and probenecid (PB) --two well-known modulators of urate transport via the proximal tubules - to evaluate their impact on urate transport through the peritoneal membrane and to clarify mechanisms affecting peritoneal transport. SETTING: A continuous ambulatory peritoneal dialysis (CAPD) unit in 2nd Hospital of IKA (Social Services Institute), Greece. PATIENTS: In 20 stable CAPD patients, on the study day, a 4-hour, 2-L, 1.36% glucose exchange was performed (control exchange). Pyrazinamide 3 g was given orally and another identical exchange was performed (study exchange). The same protocol was repeated with 2 g PB. KtN, peritoneal clearances of urea, creatinine, and urate for each exchange, and mass transfer area coefficients (MTAC) for the three solutes and their dialysate-to-plasma concentration (D/P) ratios were used to estimate peritoneal transport. RESULTS: Administration of PZA resulted in decreased clearances and MTAC values for the three solutes. The D/P ratio decreased significantly only for urate, indicating a more intense influence of PZA on urate. After PB administration, clearances of urea, creatinine, and urate were increased. MTAC and DIP ratio increased significantly only for urate (p < 0.05), demonstrating an action similar to that exerted on renal tubules. CONCLUSIONS: These findings provide evidence that unrestricted diffusion is not the only transport mechanism in the case of urate, and demonstrate the existence of an active mechanism in peritoneal urate transport with a reabsorptive and, probably, a secretive component that resembles that of renal tubule urate transport. Attention should be given in the case of CAPD patients undergoing antituberculous (PZA) treatment: it might have a negative impact on urea, creatinine, and urate peritoneal transport rates. (+info)
Vinblastine and sulfinpyrazone export by the multidrug resistance protein MRP2 is associated with glutathione export.
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The multidrug resistance proteins MRP1 and MRP2 are members of the same subfamily of ATP-binding cassette transporters. Besides organic molecules conjugated to negatively charged ligands, these proteins also transport cytotoxic drugs for which no negatively charged conjugates are known to exist. In polarized MDCKII cells, MRP1 routes to the lateral plasma membrane, and MRP2 to the apical plasma membrane. In these cells MRP1 transports daunorubicin, and MRP2 vinblastine; both transporters export reduced glutathione (GSH) into the medium. We demonstrate that glutathione transport in MDCKII-MRP1 cells is inhibited by the inhibitors of organic anion transporters sulfinpyrazone, indomethacin, probenecid and benzbromarone. In MDCKII-MRP2 cells, GSH export is stimulated by low concentrations of sulfinpyrazone or indomethacin, whereas export is inhibited down to control levels at high concentrations. We find that unmodified sulfinpyrazone is a substrate for MRP2, also at concentrations where GSH export is inhibited. We also show that GSH export in MDCKII-MRP2 cells increases in the presence of vinblastine, and that the stoichiometry between drug and GSH exported is between two and three. Our data indicate that transport of sulfinpyrazone and vinblastine is associated with GSH export. However, at high sulfinpyrazone concentrations this compound is transported without GSH. Models of MRP action are discussed that could explain these results. (+info)
Probenecid interferes with renal oxidative metabolism: a potential pitfall in its use as an inhibitor of drug transport.
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The anionic drug probenecid has been traditionally used as an inhibitor of renal organic anion transport. More recently the drug was found to inhibit organic cation transport as well, and it is used to retain intracellularly loaded fluorophores. In these investigations it is implicitly assumed that probenecid performs its activity through competition for transport. Here we studied the possibility that probenecid provokes its effect through inhibition of cellular oxidative metabolism. Oxygen consumption was measured in isolated rat kidney cortex mitochondria. At concentrations of 1 mM or higher, probenecid increased the resting state (state 4) and decreased the ADP-stimulated respiration (state 3). A complete loss in respiratory control was observed at 10 mM probenecid. After incubating isolated rat kidney proximal tubular cells (PTC) for 30 min with probenecid a concentration-dependent reduction in ATP content was observed, which was significant at concentrations of 1 mM and higher. Using digital image fluorescence microscopy the membrane potential in PTC was measured with bisoxonol. The mitochondrial effects of probenecid were paralleled by a depolarization of the plasma membrane, immediately after drug addition. All events are likely to be a result of membrane disordering due to the lipophilic character of probenecid, and may explain, at least in part, the various inhibitory effects found for the drug. We recommend to be cautious with applying probenecid in cellular research. (+info)
Riboflavin transport by isolated perfused rabbit renal proximal tubules.
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Rabbit renal proximal tubular transport of riboflavin (RF) was examined by using the in vitro isolated tubule perfusion technique. We found that proximal tubules actively reabsorbed (J(lb)) and secreted (J(bl)) RF. At 0.1 microM RF concentration, J(bl) was significantly higher than J(lb), resulting in a net secretion. This net secretion of RF was decreased at 0.01 microM RF concentration and increased at 1 microM RF concentration. Both J(lb) and J(bl) were inhibited by lowering temperature or by adding iodoacetate, a metabolic inhibitor, and lumichrome, an RF analog, suggesting the involvement of carrier-mediated transport mechanisms. J(bl) was inhibited by probenecid, an anion transport inhibitor, and by para-aminohippuric acid, an organic anion, suggesting the relevance of RF secretion to renal organic anion transport. J(bl) was also inhibited by alkaline pH (8.0) and by the calmodulin inhibitor trifluoperazine, indicating the influence of pH and Ca(2+)/calmodulin-dependent pathway on RF secretion. Finally, we found that addition of chlorpromazine, a phenothiazine derivative, inhibited both J(lb) and J(bl), raising the concern about the nutritional status in patients receiving such a type of medication. (+info)
Effects of probenecid on renal function in surgical patients anesthetized with low-flow sevoflurane.
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BACKGROUND: Dehydrofluorination of sevoflurane by carbon dioxide absorbents in anesthesia machines produces compound A, which is nephrotoxic in rats. Several clinical studies indicate that prolonged low-flow sevoflurane anesthesia is associated with an increased urinary excretion of biochemical markers, such as protein. Probenecid, a competitive inhibitor of organic anion transport, diminishes compound A nephrotoxicity in rats. The purpose of the present study was to examine the effects of low- and high-flow sevoflurane anesthesia on urinary excretion of biochemical markers in humans and to examine the effects of probenecid on urinary excretion of these markers. METHODS: Elective surgical patients (n = 64) were assigned to four groups (n = 16 each): low-flow sevoflurane plus probenecid (LSP), low-flow sevoflurane (LS), high-flow sevoflurane plus probenecid (HSP), and high-flow sevoflurane (HS). Probenecid (2.0 g) was administered orally 2 h before the induction of anesthesia in both the LSP and HSP groups. Nothing was administered orally 2 h before the induction of anesthesia in either the LS or HS groups. All patients underwent prolonged low-flow (1 l/min) or high-flow (6 l/min) sevoflurane anesthesia. Urinary excretion of protein, albumin, beta(2)-microglobulin, glucose, and N-acetyl-beta-d-glucosaminidase was measured for up to 7 days postoperatively. RESULTS: Sevoflurane doses were similar in all four groups. There were no differences in blood urea nitrogen, creatinine, or creatinine clearance among the four groups after anesthesia. Average values for urinary excretion of protein, beta(2)-microglobulin, and N-acetyl-beta-d-glucosaminidase in the LS group were significantly higher than those in the other groups (LSP, HSP, HS; P < 0.05). There was no significant difference between the LS and LSP groups in average values for urinary excretion of albumin and glucose, although there were significant differences between the LS and both high-flow sevoflurane groups (HSP, HS). CONCLUSIONS: Low-flow sevoflurane, which produces a sevenfold higher compound A exposure than high-flow sevoflurane, resulted in significant increases of several biochemical markers in half of the patients. Probenecid appears to provide protection against these renal effects. (+info)
Modelling of the blood-brain barrier transport of morphine-3-glucuronide studied using microdialysis in the rat: involvement of probenecid-sensitive transport.
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The objective of this study was to investigate the impact of probenecid on the blood-brain barrier (BBB) transport of morphine-3-glucuronide (M3G). Two groups of rats received an exponential infusion of M3G over 4 h to reach a target plasma concentration of 65 microM on two consecutive days. Probenecid was co-administered in the treatment group on day 2. Microdialysis was used to estimate unbound M3G concentrations in brain extracellular fluid (ECF) and blood. In vivo recovery of M3G was calculated with retrodialysis by drug, preceding the drug administration. The BBB transport was modelled using NONMEM. In the probenecid group, the ratio of the steady-state concentration of unbound M3G in brain ECF to that in blood was 0.08+/-0.02 in the absence and 0.16+/-0.05 in the presence of probenecid (P=0.001). In the control group, no significant difference was found in this ratio between the 2 days (0.11+/-0.05 and 0.10+/-0.02, respectively). The process that appears to be mainly influenced by probenecid is influx clearance into the brain (0.11 microl min(-1) g-brain(-1) vs 0.17 microl min(-1) g-brain(-1), in the absence vs presence of probenecid, P:<0.001). The efflux clearance was 1.15 microl min(-1) g-brain(-1). The half-life of M3G was 81+/-25 min in brain ECF vs 22+/-2 min in blood (P<0.0001). Blood pharmacokinetics was not influenced by probenecid. In conclusion, a probenecid-sensitive transport system is involved in the transport of M3G across the BBB. (+info)