CATs and HATs: the SLC7 family of amino acid transporters

The SLC7 family is divided into two subgroups, the cationic amino acid transporters (the CAT family, SLC7A1-4) and the glycoprotein-associated amino acid transporters (the gpaAT family, SLC7A5-11), also called light chains or catalytic chains of the hetero(di)meric amino acid transporters (HAT). The associated glycoproteins (heavy chains) 4F2hc (CD98) or rBAT (D2, NBAT) form the SLC3 family. Members of the CAT family transport essentially cationic amino acids by facilitated diffusion with differential trans-stimulation by intracellular substrates. In some cells, they may regulate the rate of NO synthesis by controlling the uptake of l-arginine as the substrate for nitric oxide synthase (NOS). The heterodimeric amino acid transporters are, in contrast, quite diverse in terms of substrate selectivity and function (mostly) as obligatory exchangers. Their selectivity ranges from large neutral amino acids (system L) to small neutral amino acids (ala, ser, cys-preferring, system asc), negatively charged amino acid (system xc −) and cationic amino acids plus neutral amino acids (system y+L and b0,+-like). Cotransport of Na+ is observed only for the y+L transporters when they carry neutral amino acids. Mutations in b0,+-like and y+L transporters lead to the hereditary diseases cystinuria and lysinuric protein intolerance (LPI), respectivel

CARRIER-MEDIATED UPTAKE OF H 2 -RECEPTOR ANTAGONISTS BY THE RAT CHOROID PLEXUS: INVOLVEMENT OF RAT ORGANIC ANION TRANSPORTER 3

ABSTRACT: The choroid plexus (CP) acts as a site for the elimination of xenobiotic organic compounds from the cerebrospinal fluid (CSF). The purpose of the present study is to investigate the role of rat organic anion transporter 3 (rOat3; Slc22a8) in the uptake of H 2 -receptor antagonists (cimetidine, ranitidine, and famotidine) by the isolated rat CP. Saturable uptake of cimetidine and ranitidine was observed in rOat3-LLC with K m values of 80 and 120 M, respectively, whereas famotidine was found to be a poor substrate. The steady-state concentration of the H 2 -receptor antagonists in the CSF was significantly increased by simultaneously administered probenecid, although it did not affect their brain and plasma concentrations. Saturable uptake of cimetidine and ranitidine was observed in the isolated rat CP with K m values of 93 and 170 M, respectively, whereas 50% of the uptake of famotidine remained at the highest concentration examined (1 mM). The K i value of ranitidine for the uptake of cimetidine by the isolated CP (50 M) was similar to its own K m value, suggesting that they share the same transporter for their uptake. The inhibition potency of organic anions such as benzylpenicillin, estradiol 17␤-glucuronide, p-aminohippurate, and estrone sulfate for the uptake of cimetidine by the isolated rat CP was similar to that for benzylpenicillin, the uptake of which has been hypothesized to be mediated by rOat3, whereas a minimal effect by tetraethylammonium excludes involvement of organic cation transporter(s). These results suggest that rOat3 is the most likely candidate transporter involved in regulating the CSF concentration of H 2 -receptor antagonists at the CP

Evaluation of the interaction between nonsteroidal anti-inflammatory drugs and methotrexate using human organic anion transporter 3-transfected cells

Coadministration of methotrexate and nonsteroidal anti-inflammatory drugs (NSAIDs) can cause a pharmacokinetic interaction and a subsequent increase in blood methotrexate concentrations. methotrexate and most NSAIDs are excreted into urine via organic anion transporter 3 (OAT3). The purpose of this study was to evaluate NSAIDs that compete less with methotrexate by using the renal cell line stably expressing human OAT3 (S2-hOAT3) in vitro. We also confirmed the pharmacokinetic interaction of methotrexate with NSAIDs in vivo. [3H]methotrexate uptake into S2-hOAT3 cells was inhibited by most NSAIDs in a concentration-dependent manner, but aspirin, salicylate, tiaramide, and acetaminophen did not inhibit uptake. Inhibition by sulindac and pranoprofen was weaker at therapeutic drug concentrations. Furthermore, methotrexate concentrations in rat serum were significantly increased in a NSAID concentration-dependent manner when concentrations of coadministered NSAIDs increased above the Ki values obtained in the in vitro study. On the other hand, drugs that were not substrates of hOAT3, such as acetaminophen, did not interact with methotrexate. The magnitude of the pharmacokinetic interaction between methotrexate and NSAIDs was significantly correlated with results of the accumulation study in vitro and was not significantly correlated with a reduction of urinary creatinine excretion. In conclusion, methotrexate and most NSAIDs are substrates of hOAT3, and those drugs compete via hOAT3 in tubular secretion, the major mechanism of the interaction between methotrexate and NSAIDs. The accumulation study using S2-hOAT3 cells might be useful for screening of potential interactions between methotrexate and new NSAIDs in vivo

CHARACTERIZATION OF THE RENAL TUBULAR TRANSPORT OF ZONAMPANEL, A NOVEL ␣-AMINO-3-HYDROXY-5-METHYLISOXAZOLE-4-PROPIONIC ACID RECEPTOR ANTAGONIST, BY HUMAN ORGANIC ANION TRANSPORTERS

ABSTRACT: Zonampanel monohydrate (YM872; [2,3-dioxo-7-(1H-imidazol-1-yl)-6-nitro-1,2,3,4-tetrahydro-1-quinoxalinyl]acetic acid monohydrate) is a novel ␣-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor antagonist. The major elimination route for zonampanel has been reported to be by urine via the kidneys. The purpose of this study is to elucidate the molecular mechanism of the renal excretion of zonampanel using cells stably expressing human organic anion transporters (hOAT) 1, hOAT2, hOAT3, and hOAT4, as well as human organic cation transporters The excessive synaptic release of glutamate and activation of postsynaptic glutamate receptors are considered to mediate ischemiainduced neuronal damage in stroke victims. In a wide variety of cerebral ischemia animal models, receptor antagonists against ␣-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), a glutamate receptor subtype, have been shown to be neuroprotective It has been found that the major elimination route for zonampanel monohydrate in humans and animals is by renal excretion. Zonampanel monohydrate in the body was excreted into urine mainly as the unchanged form within 2 h after completion of intravenous infusion in humans, and fecal excretion was very low (unpublished observation). In addition, renal clearance of zonampanel monohydrate was much higher than the product of the fraction unbound in plasma and the glomerular filtration rate. Therefore, it is considered that renal tubular secretion plays an important role in the renal excretion of this compound. Renal tubular secretion is accomplished through two steps of membrane transport: the uptake from blood through the basolateral mem-ABBREVIATIONS: AMPA, ␣-amino-3-hydroxy-5-methylisoxazole-4-propionic acid; OAT, organic anion transporter; OCT, organic cation transporter; hOAT, human OAT; hOCT, human OCT; PAH, para-aminohippurate; ES, estrone sulfate; D-PBS, Dulbecco's modified phosphate-buffered saline; TEA, tetraethylammonium; PG, prostaglandin, S 1 , S 2 , and S 3 , the first, second, and third segment of the proximal tubule; YM872, zonampanel monohydrate ([2,3-dioxo-7-(1H-imidazol-1-yl)-6-nitro-1,2,3,4-tetrahydro-1-quinoxalinyl]acetic acid monohydrate); YM90K, 6-(1H-imidazol-1-yl)-7-nitro-2,3(1H,4H)-quinoxalinedione monohydrochloride

Molecular Mechanism of Ochratoxin A Transport in the Kidney

The mycotoxin, ochratoxin A (OTA), is thought to be responsible for Balkan endemic nephropathy. OTA accumulates in several tissues, especially in the kidneys and liver. The excretion of OTA into urine is thought to be mainly by tubular secretion, presumably via the organic anion transport system. Recently, several families of multispecific organic anion transporters have been identified: organic anion transporters (OATs), organic anion-transporting polypeptides (OATPs), oligopeptide transporters (PEPTs), and ATP-binding cassette (ABC) transporters, such as MRP2 and BCRP. These renal transporters mediate the transmembrane transport of OTA and play a pivotal role in the development of OTA-induced nephrotoxicity

Invariant NKT cells metabolically adapt to the acute myeloid leukaemia environment

Acute myeloid leukaemia (AML) creates an immunosuppressive environment to conventional T cells through Arginase 2 (ARG2)-induced arginine depletion. We identify that AML blasts release the acute phase protein serum amyloid A (SAA), which acts in an autocrine manner to upregulate ARG2 expression and activity, and promote AML blast viability. Following in vitro cross-talk invariant natural killer T (iNKT) cells become activated, upregulate mitochondrial capacity, and release IFN-γ. iNKT retain their ability to proliferate and be activated despite the low arginine AML environment, due to the upregulation of Large Neutral Amino Acid Transporter-1 (LAT-1) and Argininosuccinate Synthetase 1 (ASS)-dependent amino acid pathways, resulting in AML cell death. T cell proliferation is restored in vitro and in vivo. The capacity of iNKT cells to restore antigen-specific T cell immunity was similarly demonstrated against myeloid-derived suppressor cells (MDSCs) in wild-type and Jα18−/− syngeneic lymphoma-bearing models in vivo. Thus, stimulation of iNKT cell activity has the potential as an immunotherapy against AML or as an adjunct to boost antigen-specific T cell immunotherapies in haematological or solid cancers

Metabolic Acidosis Alters Expression of Slc22 Transporters in Mouse Kidney

INTRODUCTION The kidneys play a central role in eliminating metabolic waste products and drugs through transporter-mediated excretion along the proximal tubule. This task is mostly achieved through a variety of transporters from the solute carrier family 22 (SLC22) family of organic cation and anion transporters. Metabolic acidosis modulates metabolic and renal functions and also affects the clearance of metabolites and drugs from the body. We had previously shown that induction of metabolic acidosis in mice alters a large set of transcripts, among them also many transporters including transporters from the Slc22 family. OBJECTIVE Here we further investigated the impact of acidosis on Slc22 family members. METHODS Metabolic acidosis was induced for 2 or 7 days with NH4Cl, some animals also received the uricase inhibitor oxonic acid for comparison. Expression of transporters was studied by qPCR and immunoblotting. RESULTS NH4Cl induced no significant changes in plasma or urine uric acid levels but caused downregulation of Slc22a1 (Oct1), Slc22a6 (Oat1), Slc22a19 (Oat5), and -Slc22a12 (Urat1) at mRNA level. In contrast, Slc22a4 mRNA (Octn1) was upregulated. On protein level, NH4Cl increased Octn1 (after 7 days) and Urat1 (after 2 days) abundance and decreased Oat1 (after 2 days) and Urat1 (after 7 days). Oxonic acid had no impact on protein abundance of any of the transporters tested. CONCLUSION In summary, metabolic acidosis alters expression of several transporters involved in renal excretion of metabolic waste products and drugs. This may have implications for drug kinetics and clearance of waste metabolites