Molecular pharmacology of renal organic anion transporters

Renal organic anion transport systems play an important role in the elimination of drugs, toxic compounds, and their metabolites, many of which are potentially harmful to the body. The renal proximal tubule is the primary site of carrier-mediated transport from blood to urine of a wide variety of anionic substrates. Recent studies have shown that organic anion secretion in renal proximal tubule is mediated by distinct sodium-dependent and sodium-independent transport systems. Knowledge of the molecular identity of these transporters and their substrate specificity has increased considerably in the past few years by cloning of various carrier proteins. However, a number of fundamental questions still have to be answered to elucidate the participation of the cloned transporters in the overall tubular secretion of anionic xenobiotics. This review summarizes the latest knowledge on molecular and pharmacological properties of renal organic anion transporters and homologs, with special reference to their nephron and plasma membrane localization, transport characteristics, and substrate and inhibitor specificity. A number of the recently cloned transporters, such as the p-aminohippurate/dicarboxylate exchanger OAT1, the anion/sulfate exchanger SAT1, the peptide transporters PEPT1 and PEPT2, and the nucleoside transporters CNT1 and CNT2, are key proteins in organic anion handling that possess the same characteristics as has been predicted from previous physiological studies. The role of other cloned transporters, such as MRP1, MRP2, OATP1, OAT-K1, and OAT-K2, is still poorly characterized, whereas the only information that is available on the homologs OAT2, OAT3, OATP3, and MRP3–6 is that they are expressed in the kidney, but their localization, not to mention their function, remains to be elucidated.

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Organic anion transporters 1 and 3 influence cellular energy metabolism in renal proximal tubule cells

Biological Chemistry ◽

10.1515/hsz-2018-0446 ◽

2019 ◽

Vol 400 (10) ◽

pp. 1347-1358 ◽

Cited By ~ 4

Author(s):

Jelle Vriend ◽

Charlotte A. Hoogstraten ◽

Kevin R. Venrooij ◽

Bartholomeus T. van den Berge ◽

Larissa P. Govers ◽

...

Keyword(s):

Proximal Tubule ◽

Organic Anion ◽

Depth Profiling ◽

Tca Cycle ◽

Oxidative Capacity ◽

Organic Anion Transporters ◽

Anion Transporters ◽

Oxidative Phenotype ◽

Underlying Mechanisms ◽

Lactate Levels

Abstract Organic anion transporters (OATs) 1 and 3 are, besides being uptake transporters, key in several cellular metabolic pathways. The underlying mechanisms are largely unknown. Hence, we used human conditionally immortalized proximal tubule epithelial cells (ciPTEC) overexpressing OAT1 or OAT3 to gain insight into these mechanisms. In ciPTEC-OAT1 and -OAT3, extracellular lactate levels were decreased (by 77% and 71%, respectively), while intracellular ATP levels remained unchanged, suggesting a shift towards an oxidative phenotype upon OAT1 or OAT3 overexpression. This was confirmed by increased respiration of ciPTEC-OAT1 and -OAT3 (1.4-fold), a decreased sensitivity to respiratory inhibition, and characterized by a higher demand on mitochondrial oxidative capacity. In-depth profiling of tricarboxylic acid (TCA) cycle metabolites revealed reduced levels of intermediates converging into α-ketoglutarate in ciPTEC-OAT1 and -OAT3, which via 2-hydroxyglutarate metabolism explains the increased respiration. These interactions with TCA cycle metabolites were in agreement with metabolomic network modeling studies published earlier. Further studies using OAT or oxidative phosphorylation (OXPHOS) inhibitors confirmed our idea that OATs are responsible for increased use and synthesis of α-ketoglutarate. In conclusion, our results indicate an increased α-ketoglutarate efflux by OAT1 and OAT3, resulting in a metabolic shift towards an oxidative phenotype.

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Developmental expression of renal organic anion transporters in rat kidney and its effect on renal secretion of phenolsulfonphthalein

AJP Renal Physiology ◽

10.1152/ajprenal.00525.2011 ◽

2012 ◽

Vol 302 (12) ◽

pp. F1640-F1649 ◽

Cited By ~ 15

Author(s):

Maki Nomura ◽

Hideyuki Motohashi ◽

Hiroko Sekine ◽

Toshiya Katsura ◽

Ken-ichi Inui

Keyword(s):

Protein Expression ◽

Organic Anion ◽

Immunohistochemical Analysis ◽

Tubular Secretion ◽

Organic Anion Transporters ◽

Adult Rats ◽

Anion Transporters ◽

Anionic Drugs ◽

Clearance Study

Organic anion transporters (OAT1 and OAT3) and multidrug resistance-associated proteins (MRP2 and MRP4) play important roles in anionic drug secretion in renal proximal tubules. Changes in the expression of such transporters are considered to affect the tubular secretion of anionic drugs. The purpose of this study was to elucidate the developmental changes in the expression of OAT1, OAT3, MRP2, and MRP4 and their effects on the tubular secretion of drugs. The mRNA level of each transporter was measured by real-time PCR, and the protein expression was evaluated by Western blotting and immunohistochemical analysis. In addition, the tubular secretion of phenolsulfonphthalein (PSP) in infant (postnatal day 14) and adult rats was estimated based on in vivo clearance study. The protein expression of organic anion transporters were very low at postnatal day 0 and gradually increased with age. In postnatal day 14 rats, the expression of OAT1 and OAT3 seemed to be at almost mature levels, while MRP2 and MRP4 seemed to be at immature levels. Immunohistochemical analysis in the kidney of postnatal day 0 rats revealed OATs on the basolateral membrane and MRPs on the brush-border membrane. At postnatal day 0, the distribution of these transporters was restricted to the inner cortical region, while after postnatal day 14, it was identical to that in adult kidney. An in vivo clearance study revealed that the tubular secretion of PSP was significantly lower in postnatal day 14 rats than adult rats. These results indicate that age-dependent changes in organic anion transporter expression affect the tubular secretion of anionic drugs in pediatric patients.

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Murine renal organic anion transporters mOAT1 and mOAT3 facilitate the transport of neuroactive tryptophan metabolites

AJP Cell Physiology ◽

10.1152/ajpcell.00619.2004 ◽

2005 ◽

Vol 289 (5) ◽

pp. C1075-C1084 ◽

Cited By ~ 59

Author(s):

Andrew Bahn ◽

Marija Ljubojević ◽

Heiko Lorenz ◽

Christian Schultz ◽

Estifanos Ghebremedhin ◽

...

Keyword(s):

Organic Anion ◽

Significant Inhibition ◽

The Body ◽

Organic Anion Transporters ◽

Bioactive Substances ◽

Anion Transporters ◽

Tryptophan Metabolites ◽

Cortex Cerebri ◽

Stimulation Experiments ◽

Almost All

Tryptophan metabolites such as kynurenate (KYNA), xanthurenate (XA), and quinolinate are considered to have an important impact on many physiological processes, especially brain function. Many of these metabolites are secreted with the urine. Because organic anion transporters (OATs) facilitate the renal secretion of weak organic acids, we investigated whether the secretion of bioactive tryptophan metabolites is mediated by OAT1 and OAT3, two prominent members of the OAT family. Immunohistochemical analyses of the mouse kidneys revealed the expression of OAT1 to be restricted to the proximal convoluted tubule (representing S1 and S2 segments), whereas OAT3 was detected in almost all parts of the nephron, including macula densa cells. In the mouse brain, OAT1 was found to be expressed in neurons of the cortex cerebri and hippocampus as well as in the ependymal cell layer of the choroid plexus. Six tryptophan metabolites, including the bioactive substances KYNA, XA, and the serotonin metabolite 5-hydroxyindol acetate inhibited [3H] p-aminohippurate (PAH) or 6-carboxyfluorescein (6-CF) uptake by 50–85%, demonstrating that these compounds interact with OAT1 as well as with OAT3. Half-maximal inhibition of mOAT1 occurred at 34 μM KYNA and 15 μM XA, and it occurred at 8 μM KYNA and 11.5 μM XA for mOAT3. Quinolinate showed a slight but significant inhibition of [3H]PAH uptake by mOAT1 and no alteration of 6-CF uptake by mOAT3. [14C]-Glutarate (GA) uptake was examined for both transporters and demonstrated differences in the transport rate for this substrate by a factor of 4. Trans-stimulation experiments with GA revealed that KYNA and XA are substrates for mOAT1. Our results support the idea that OAT1 and OAT3 are involved in the secretion of bioactive tryptophan metabolites from the body. Consequently, they are crucial for the regulation of central nervous system tryptophan metabolite concentration.

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Carrier-mediated transport of quercetin conjugates: Involvement of organic anion transporters and organic anion transporting polypeptides

Biochemical Pharmacology ◽

10.1016/j.bcp.2012.05.011 ◽

2012 ◽

Vol 84 (4) ◽

pp. 564-570 ◽

Cited By ~ 26

Author(s):

Chi Chun Wong ◽

Yasutoshi Akiyama ◽

Takaaki Abe ◽

Jonathan D. Lippiat ◽

Caroline Orfila ◽

...

Keyword(s):

Organic Anion ◽

Organic Anion Transporters ◽

Organic Anion Transporting Polypeptides ◽

Anion Transporters ◽

Carrier Mediated Transport

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Interactions of organic anions with the organic cation transporter in renal BBMV

AJP Renal Physiology ◽

10.1152/ajprenal.1988.254.1.f56 ◽

1988 ◽

Vol 254 (1) ◽

pp. F56-F61 ◽

Cited By ~ 2

Author(s):

P. H. Hsyu ◽

L. G. Gisclon ◽

A. C. Hui ◽

K. M. Giacomini

Keyword(s):

Proximal Tubule ◽

Organic Cation ◽

Organic Anion ◽

Organic Cation Transporter ◽

Organic Anions ◽

Renal Proximal Tubule ◽

Ph Gradient ◽

Transport Systems ◽

Organic Cations ◽

Initial Uptake

It is generally assumed that the organic cation transport system in the renal proximal tubule is specific for organic cations and the transport of organic cations is not affected by organic anions. However, there are also data in the literature demonstrating that probenecid, a classical inhibitor of organic anion transport systems, inhibits the transport of an organic cation, cimetidine, in the renal proximal tubule. In this study we investigated the effects of probenecid and furosemide on the transport of N'-methylnicotinamide (NMN) the classical substrate of the organic cation transporter, in brush-border membrane vesicles prepared from rabbit renal cortex. In the presence of a pH gradient, both probenecid (10 mM) and furosemide reduced the initial uptake of NMN. Probenecid reduced the initial uptake of NMN to 12.1% of the control values (1.19 +/- 0.26 pmol/mg) and furosemide reduced the initial uptake of NMN to 39.2%. Probenecid (10 mM) also decreased the initial transport of NMN in the absence of a pH gradient. Inhibition of the transport of NMN by probenecid was concentration dependent, with the concentration of probenecid resulting in 50% inhibition of the transport of NMN equal to 2.31 +/- 1.18 mM in the presence of a pH gradient. Probenecid appeared to be a competitive inhibitor of NMN transport. The apparent Km (mean +/- SE) of NMN transport (2.01 +/- 0.78 mM) was increased to 18.7 +/- 10 mM (P less than 0.05) by probenecid (10 mM), whereas the Vmax was not changed (125 +/- 19.2 pmol.s-1.mg-1 vs. 186 +/- 94 pmol.s-1.mg-1, P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

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