Objective. Serum uric acid (SUA) levels in humans are mainly regulated by urate transporters. Recent genome-wide association studies suggested that common variants of the human sodium-dependent phosphate cotransporter type 1 gene (NPT1/SLC17A1) influence SUA. NPT1 has been reported to mediate urate transport, but its physiologic role in regulating SUA in humans remains unclear. Furthermore, the findings of replication studies of the relationship between NPT1 variants and gout have been inconsistent. The aims of this study were to investigate the effect of NPT1 on gout and to determine its physiologic role.Methods. Five hundred forty-five male Japanese patients with gout and 1,115 male Japanese control subjects were genotyped for rs1165196 (I269T), a common missense variant in NPT1. Analyses of the association between rs1165196 and gout were then conducted, focusing especially on renal underexcretion (RUE) gout. Immunohistochemical analysis and functional analysis using Xenopus oocytes were also performed.Results. Single-nucleotide polymorphism rs1165196 significantly decreased the risk of RUE gout (odds ratio 0.73, P ‫؍‬ 0.031) but did not confer a risk for all gout (P ‫؍‬ 0.123). The immunohistochemical analysis revealed that human NPT1 is localized to the apical membrane of the renal proximal tubule. The functional analysis using Xenopus oocyte expression systems showed that rs1165196 increases NPT1-mediated urate export.Conclusion. This study showed that NPT1 is a urate exporter located in the renal proximal tubule in humans, and that its common gain-of-function variant, rs1165196, causes RUE gout, a major subtype of gout. These findings enable us to deepen our understanding

In addition to epithelial cells, macrophages, vascular endothelial cells, and B lymphocytes contained activated NF-kappaB. In these cells, activated NF-kappaB may be involved in the inflammation process in HAG through the up-regulation of chemokines or adhesion molecules.

Aim: To determine whether a 5‐day regimen with rabeprazole, clarithromycin and amoxicillin (RCA) was as effective as a 7‐day regimen. Methods: A total of 139 H. pylori‐infected patients were randomized to receive either a 5‐day or 7‐day course of rabeprazole 10 mg b.d., clarithromycin 400 mg b.d. and amoxicillin 750 mg b.d. Eradication was assessed by CLO test, histology and 13C‐urea breath test. Results: On the intention‐to‐treat basis, eradication rates were 66% (46 out of 70) and 84% (58 out of 69) for the 5‐ and 7‐day regimens, respectively (P < 0.05). Using per protocol analysis, eradication rates were 70% (46 out of 66) and 91% (58 out of 64) for the 5‐ and 7‐day regimens, respectively (P < 0.01). Adverse events, which were observed in 14 patients from each group, caused discontinuation of treatment in only two patients, resulting in excellent compliance. Conclusions: Our 5‐day regimen of RCA yielded inferior results, whereas the 7‐day regimen achieved an eradication rate exceeding 90% on the per protocol basis. Therefore, treatment regimens of less than 7 days for proton pump inhibitor–clarithromycin–amoxicillin therapies cannot be recommended.

ϩ -dependent phosphate cotransporter (NaPi-IIc) is specifically targeted to, and expressed on, the apical membrane of renal proximal tubular cells and mediates phosphate transport. In the present study, we investigated the signals that determine apical expression of NaPi-IIc with a focus on the role of the N-and the C-terminal tails of mouse NaPi-IIc in renal epithelial cells [opossum kidney (OK) and Madin-Darby canine kidney cells]. Wild-type NaPi-IIc, the cotransporter NaPi-IIa, as well as several IIa-IIc chimeras and deletion mutants, were fused to enhanced green fluorescent protein (EGFP), and their cellular localization was analyzed in polarized renal epithelial cells by confocal microscopy and by cell-surface biotinylation. Fluorescent EGFP-fused NaPi-IIc transporter proteins are correctly expressed in the apical membrane of OK cells. The apical expression of N-terminal deletion mutants (deletion of N-terminal 25, 50, or 69 amino acids) was not affected by truncation. In contrast, C-terminal deletion mutants (deletion of C-terminal 45, 50, or 62 amino acids) did not have correct apical expression. A more detailed mutational analysis indicated that a domain (amino acids WLHSL) in the cytoplasmic C terminus is required for apical expression of NaPi-IIc in renal epithelial cells. We conclude that targeting of NaPi-IIc to the apical cell surface is regulated by a unique amino acid motif in the cytoplasmic C-terminal domain.Npt2c; SLC34A3; localization; OK cell; hereditary hypophosphatemic rickets with hypercalciuria INORGANIC PHOSPHATE (P i ) reabsorption in renal proximal tubules is required for P i homeostasis in the body. Na ϩ -dependent P i transporters (NaPi) in the brush-border membrane (BBM) of proximal tubule cells mediate the rate-limiting step in the overall P i -reabsorption process (26,28). Type IIa (NaPiIIa) and type IIc (NaPi-IIc) NaPi cotransporters are expressed in the apical membrane of proximal tubule cells and mediate P i transport (27, 38). The extent of P i reabsorption in the proximal tubules is determined largely by the abundance of the NaPi-IIa cotransporter (11,28,29).Several groups have shown that hereditary hypophosphatemic rickets with hypercalciuria (HHRH), a Mendelian disorder of renal P i reabsorption (39, 42), results from the lack of a functional NaPi-IIc protein, leading to severe renal wasting with hypophosphatemia (5,16,19,22,25). These data suggest that the NaPi-IIc cotransporter plays an important role in renal P i reabsorption and may be a key determinant of plasma P i concentrations in humans. However, it is not clear why a loss of function of the less abundant and energetically less favorable electroneutral NaPi-IIc transporter causes hypophosphatemia/rickets and osteomalacia in humans, whereas mutations in the more abundant electrogenic NaPi-IIa elicits a mild skeletal phenotype (3).The plasma membrane of epithelial cells is divided into two separate membrane compartments, the apical and the basolateral domains (36,37). This polarity is maintained by intracellular mach...

Mutations in the apically located Na(+)-dependent phosphate (NaPi) cotransporter, SLC34A3 (NaPi-IIc), are a cause of hereditary hypophosphatemic rickets with hypercalciuria (HHRH). We have characterized the impact of several HHRH mutations on the processing and stability of human NaPi-IIc. Mutations S138F, G196R, R468W, R564C, and c.228delC in human NaPi-IIc significantly decreased the levels of NaPi cotransport activities in Xenopus oocytes. In S138F and R564C mutant proteins, this reduction is a result of a decrease in the V(max) for P(i), but not the K(m). G196R, R468W, and c.228delC mutants were not localized to oocyte membranes. In opossum kidney (OK) cells, cell surface labeling, microscopic confocal imaging, and pulse-chase experiments showed that G196R and R468W mutations resulted in an absence of cell surface expression owing to endoplasmic reticulum (ER) retention. G196R and R468W mutants could be partially stabilized by low temperature. In blue native-polyacrylamide gel electrophoresis analysis, G196R and R468W mutants were either denatured or present in an aggregation complex. In contrast, S138F and R564C mutants were trafficked to the cell surface, but more rapidly degraded than WT protein. The c.228delC mutant did not affect endogenous NaPi uptake in OK cells. Thus, G196R and R468W mutations cause ER retention, while S138F and R564C mutations stimulate degradation of human NaPi-IIc in renal epithelial cells. Together, these data suggest that the NaPi-IIc mutants in HHRH show defective processing and stability.