Extra-Renal Elimination of Uric Acid via Intestinal Efflux Transporter BCRP/ABCG2

Urinary excretion accounts for two-thirds of total elimination of uric acid and the remainder is excreted in feces. However, the mechanism of extra-renal elimination is poorly understood. In the present study, we aimed to clarify the mechanism and the extent of elimination of uric acid through liver and intestine using oxonate-treated rats and Caco-2 cells as a model of human intestinal epithelium. In oxonate-treated rats, significant amounts of externally administered and endogenous uric acid were recovered in the intestinal lumen, while biliary excretion was minimal. Accordingly, direct intestinal secretion was thought to be a substantial contributor to extra-renal elimination of uric acid. Since human efflux transporter BCRP/ABCG2 accepts uric acid as a substrate and genetic polymorphism causing a decrease of BCRP activity is known to be associated with hyperuricemia and gout, the contribution of rBcrp to intestinal secretion was examined. rBcrp was confirmed to transport uric acid in a membrane vesicle study, and intestinal regional differences of expression of rBcrp mRNA were well correlated with uric acid secretory activity into the intestinal lumen. Bcrp1 knockout mice exhibited significantly decreased intestinal secretion and an increased plasma concentration of uric acid. Furthermore, a Bcrp inhibitor, elacridar, caused a decrease of intestinal secretion of uric acid. In Caco-2 cells, uric acid showed a polarized flux from the basolateral to apical side, and this flux was almost abolished in the presence of elacridar. These results demonstrate that BCRP contributes at least in part to the intestinal excretion of uric acid as extra-renal elimination pathway in humans and rats

Moderate Molecular Recognitions on ZnO m-Plane and Their Selective Capture/Release of Bio-related Phosphoric Acids

Herein, we explore the hidden molecular recognition abilities of ZnO nanowires uniformly grown on the inner surface of an open tubular fused silica capillary via liquid chromatography. Chromatographic evaluation revealed that ZnO nanowires showed a stronger intermolecular interaction with phenylphosphoric acid than any other monosubstituted benzene. Furthermore, ZnO nanowires specifically recognized the phosphate groups present in nucleotides even in the aqueous mobile phase, and the intermolecular interaction increased with the number of phosphate groups. This discrimination of phosphate groups in nucleotides was unique to the rich (10[1 with combining macron]0) m-plane of ZnO nanowires with a moderate hydrophilicity and negative charge. The discrimination could be evidenced by the changes in the infrared bands of the phosphate groups on nucleotides on ZnO nanowires. Finally, as an application of the molecular recognition, nucleotides were separated by the number of phosphate groups, utilizing optimized gradient elution on ZnO nanowire column. Thus, the present results elucidate the unique and versatile molecular selectivity of well-known ZnO nanostructures for the capture and separation of biomolecules

Uric acid transport by ABC transporters.

<p>(A) Uptake of [¹⁴C]uric acid (20 µM) by vesicles expressing rat and human ABC transporters was measured for 5 min at 37°C in the presence of 4 mM ATP (closed symbols) or AMP (open symbols). (B) Concentration dependency of and (C) inhibition study for rBcrp-mediated uptake were studied. Inhibition study was performed in the absence or the presence of various inhibitors at indicated concentrations. ATP-dependent uptake was obtained by subtracting uric acid uptake in the presence of AMP from that in the presence of ATP, and the solid line was drawn by fitting based on non-linear least-squares regression analysis. Saturable transport of uric acid is also shown as an Eadie-Hofstee plot. Each bar shows the mean ± S.E.M. (n = 3–6). An asterisk (*) shows a significant difference from (A and B) uric acid uptake in the presence of AMP and (C) uric acid uptake in the absence of inhibitors by Student's t-test (<i>p</i><0.05).</p

Intestinal secretion of uric acid and regional difference of Bcrp-mRNA expression.

<p>(A) Intestinal clearance of uric acid at each of jejunum, ileum, and colon was determined by means of the <i>in situ</i> intestinal closed loop method in oxonate-treated rats in the absence (Control, open bars) and presence of elacridar (10 µM, closed bars). Each bar indicates the mean ± S.E.M. (n = 3–8). An asterisk (*) shows a significant difference from the control by Student's t-test (<i>p</i><0.05), and double asterisks (**) show a significant difference from ileum by Student's t-test (<i>p</i><0.05). (B) Level of BCRP mRNA expression was determined in different region of intestine in oxonate-treated rats, and then normalized to rat Gapdh. Each bar indicates the mean ± S.E.M. (n = 6). Expression intensity in jejunum was individually set to 1 and the intensities of ileum and colon were calculated relative to it. An asterisk (*) shows a significant difference from ileum by Student's t-test (<i>p</i><0.05).</p

Effect of elacridar on intestinal secretion and rBcrp-mediated uric acid uptake.

<p>(A) Intestinal clearance of uric acid at the ileum was determined by means of the <i>in situ</i> intestinal closed loop method in the absence (Control, white bar) and presence of 0.1 (gray bar) and 10 µM elacridar (black bar). Each bar indicates the mean ± S.E.M. (n = 4–8). An asterisk (*) shows a significant difference from the control by Student's t-test (<i>p</i><0.05). (B) Uptake of [¹⁴C]uric acid (20 µM) by membrane vesicles was measured for 5 min at 37°C in the absence (Control, open bar) and presence of 0.1 (gray bar) or 10 µM elacridar (closed bar). Each bar shows the mean ± S.E.M. (n = 3–6). An asterisk (*) shows a significant difference from uric acid uptake in the absence of elacridar by Student's t-test (<i>p</i><0.05).</p

Plasma uric acid concentration and its intestinal and renal clearance in oxonate-treated mice.

<p>(A) Plasma uric acid concentration, (B) intestinal clearance at the ileum, and (C) renal clearance were measured in oxonate-treated wild-type (open symbols) and <i>Bcrp1^−/−</i> (closed symbols) mice by means of the intestinal closed loop method and metabolic cages. Each value indicates the mean ± S.E.M. (n = 4–5). An asterisk (*) shows a significant difference from wild-type mice by Student's t-test (<i>p</i><0.05).</p

Clearance of endogenous uric acid in oxonate-treated rats.

<p>Clearance of endogenous uric acid was measured in oxonate-treated rats. Urine, bile and blood were collected up to 60 min and clearances were calculated by dividing the amount excreted into each part by plasma AUC. Estimated intestinal clearance was obtained as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030456#s4" target="_blank">Materials and methods</a> using mean value of 5 individual measurements; 118±2.52 cm for length for jejunum and 15.7±0.33 cm for colon, respectively. Values indicate mean ± S.E.M. (n = 5).</p