Identification of novel inhibitors of the steroid sulfate carrier ‘sodium-dependent organic anion transporter’ SOAT (SLC10A6) by pharmacophore modelling

Human trophoblasts depend on the supply of external precursors, such as dehydroepiandrosterone-3-sulfate (DHEA-S) and 16α-OH-DHEA-S, for synthesis of estrogens. The aim of the present study was to characterize the uptake of DHEA-S by isolated mononucleated trophoblasts (MT) and to identify the involved transporter polypeptides. The kinetic analysis of DHEA-35S uptake by MT revealed a saturable uptake mechanism ( K m = 26 μM, V max = 428 pmol · mg protein−1 · min−1), which was superimposed by a nonsaturable uptake mechanism (diffusion constant = 1.2 μl · mg protein−1 · min−1). Uptake of [3H]DHEA-S by MT was Na+dependent and inhibited by sulfobromophthalein (BSP), steroid sulfates, and probenecid, but not by steroid glucuronides, unconjugated steroids, conjugated bile acids, ouabain, p-aminohippurate (PAH), and bumetanide. MT took up [35S]BSP, [3H]estrone-sulfate, but not 3H-labeled ouabain, estradiol-17β-glucuronide, taurocholate, and PAH. RT-PCR revealed that the organic anion-transporting polypeptides OATP-B, -D, -E, and the organic anion transporter OAT-4 are highly expressed, and that OATP-A, -C, -8, OAT-3, and Na+-taurocholate cotransporting polypeptide (NTCP) are not or are only lowly expressed in term placental tissue and freshly isolated and cultured trophoblasts. Immunohistochemistry of first- and third-trimester placenta detected OAT-4 on cytotrophoblast membranes and at the basal surface of the syncytiotrophoblast. Our results indicate that uptake of steroid sulfates by isolated MT is mediated by OATP-B and OAT-4 and suggest a physiological role of both carrier proteins in placental uptake of fetal-derived steroid sulfates.

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Organic anion transporter OAT1 is involved in renal handling of citrulline

AJP Renal Physiology ◽

10.1152/ajprenal.90662.2008 ◽

2009 ◽

Vol 297 (1) ◽

pp. F71-F79 ◽

Cited By ~ 20

Author(s):

Masanori Nakakariya ◽

Yoichiro Shima ◽

Yoshiyuki Shirasaka ◽

Keisuke Mitsuoka ◽

Takeo Nakanishi ◽

...

Keyword(s):

Rat Kidney ◽

Organic Anion ◽

Relative Activity ◽

Organic Anion Transporter ◽

Renal Handling ◽

Functional Sites ◽

Kidney Slices ◽

Anion Transporter ◽

Activity Factor ◽

Sodium Dependent

Because citrulline plasma concentration is elevated in kidney failure, citrulline could be a biomarker of renal insufficiency, although the mechanism regulating its disposition in the kidney has not been clarified. In rat kidney slices, citrulline uptake was apparently Na+ dependent, saturable with Km 556 μM, and significantly inhibited by anionic (PAH) and cationic (TEA) compounds, but not by probenecid at 1 mM. Preincubation of kidney slices with glutarate increased citrulline uptake, while such an increase was not observed after preincubation of the slices in Na+-free buffer. This result suggested that a sodium-dependent dicarboxylate cotransporter is involved in citrulline uptake by rat kidney slices. In studies using transporter-overexpressing cells, human organic anion transporter 1 (OAT1) and rat Oat1 exhibited citrulline transport activity with Km values of 238 and 373 μM, respectively, while other OATs and organic cation transporters (OCTs) did not transport citrulline. Based on the relative activity factor method, the contribution of rat Oat1 to the overall uptake of citrulline in rat kidney slices was ∼70%. Moreover, the interaction among citrulline, PAH, and probenecid uptakes via rat Oat1 suggested that there are multiple functional sites on Oat1 and that the citrulline site may be distinct from the PAH and probenecid site. Thus OAT1/Oat1 appears to be one of the major contributors to renal basolateral uptake of citrulline, and impaired activities of these transporters may contribute substantially to the increase in plasma citrulline in renal failure. Accordingly, citrulline may be useful for diagnosis of kidney function as is creatinine.

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