SLC2A9 is a newly identified urate transporter influencing serum urate concentration, urate excretion and gout

Does an apple a day put hypertension in play?

Singh et al. offer exciting data in their new report about fructose-induced hypertension. Fructose induced an increase in serum uric acid after 8-10 weeks of increased fructose exposure, but no correlation was found between hyperuricemia and hypertension.

GLUT7: a new intestinal facilitated hexose transporter

The very last member of the SLC2A gene family of facilitated hexose transporters to be cloned was SLC2A7 (hGLUT7). It has been assigned to the class II of the GLUT family on the basis of sequence similarity, and its closest family member is GLUT5, an intestinal fructose transporter. GLUT7 is primarily expressed in the small intestine and colon, although mRNA has been detected in the testis and prostate as well. The protein is expressed in the apical membrane of the small intestine and colon, and it has a high affinity (<0.5 mM) for glucose and fructose. The abundance of the protein in the small intestine does change in parallel with the dietary carbohydrate. However, the distribution of GLUT7 along the small intestine does not entirely match with the availability of glucose and fructose, suggesting that the physiological substrate for this transporter has yet to be identified. Unlike GLUT13, the proton-coupled myoinositol transporter (HMIT), there is no evidence for the coupling of protons to the hexose movement via GLUT7. One area of study in which GLUT7 has provided a useful comparison with GLUT1 has been in the development of the hypothesis that the facilitated hexose transporters may have a selectivity filter at the exofacial opening of the translocation pore, which helps to determine which hexoses can be transported. If substantiated, the elucidation of this mechanism may prove useful in the design of hexose analogs for use in cancer imaging and therapeutics.

Sex-specific association of the putative fructose transporter SLC2A9 variants with uric acid levels is modified by BMI

OBJECTIVE

High serum uric acid levels lead to gout and have been reported to be associated with an increased risk of hypertension, obesity, metabolic syndrome, type 2 diabetes, and cardiovascular disease. Recently, the putative fructose transporter SLC2A9 was reported to influence uric acid levels. The aim of the present study was to examine the association of four single nucleotide polymorphisms within this gene with uric acid levels and to determine whether this association is modified by obesity.

RESEARCH DESIGN AND METHODS

Four single nucleotide polymorphisms within SLC2A9 (rs6855911, rs7442295, rs6449213, and rs12510549) were genotyped in the population-based prospective Bruneck Study (n = 800) and in a case-control study from Utah including 1,038 subjects recruited for severe obesity and 831 control subjects.

RESULTS

We observed highly significant associations between all four polymorphisms and uric acid levels in all study groups. Each copy of the minor allele decreased age- and sex-adjusted uric acid levels by 0.30-0.35 mg/dl on average, which translates to a relative decrease of 5-6% with P values ranging from 10(-9) to 10(-11) in the combined analysis. An extended adjustment for BMI, creatinine, gout medication, and alcohol intake improved P values to a range of 10(-14) to 10(-20). The association was more pronounced in women and the population-based Bruneck Study and was significantly modified by BMI, with stronger effect sizes in individuals with high BMI.

CONCLUSIONS

Genetic variants within SLC2A9 have significant effects on uric acid levels and are modified by sex and BMI.

Genetic determinants of phenotypic diversity in humans

New techniques are enabling the identification of genetic variants underlying complex diseases and phenotypic traits.

New technologies for rapidly assaying DNA sequences have revealed that the degree and nature of human genetic variation is far more complex then previously realized. These same technologies have also resulted in the identification of common genetic variants associated with more than 30 human diseases and traits.

Identification of a new urate and high affinity nicotinate transporter, hOAT10 (SLC22A13)

The orphan transporter hORCTL3 (human organic cation transporter like 3; SLC22A13) is highly expressed in kidneys and to a weaker extent in brain, heart, and intestine. hORCTL3-expressing Xenopus laevis oocytes showed uptake of [(3)H]nicotinate, [(3)H]p-aminohippurate, and [(14)C]urate. Hence, hORCTL3 is an organic anion transporter, and we renamed it hOAT10. [(3)H]Nicotinate transport by hOAT10 into X. laevis oocytes and into Caco-2 cells was saturable with Michaelis constants (K(m)) of 22 and 44 microm, respectively, suggesting that hOAT10 may be the molecular equivalent of the postulated high affinity nicotinate transporter in kidneys and intestine. The pH dependence of hOAT10 suggests p-aminohippurate(-)/OH(-), urate(-)/OH(-), and nicotinate(-)/OH(-) exchange as possible transport modes. Urate inhibited [(3)H]nicotinate transport by hOAT10 with an IC(50) value of 759 microm, assuming that hOAT10 represents a low affinity urate transporter. hOAT10-mediated [(14)C]urate uptake was elevated by an exchange with l -lactate, pyrazinoate, and nicotinate. Surprisingly, we have detected urate(-)/glutathione exchange by hOAT10, consistent with an involvement of hOAT10 in the renal glutathione cycle. Uricosurics, diuretics, and cyclosporine A showed substantial interactions with hOAT10, of which cyclosporine A enhanced [(14)C]urate uptake, providing the first molecular evidence for cyclosporine A-induced hyperuricemia.