SGLT2 inhibition and renal urate excretion: role of luminal glucose, GLUT9, and URAT1

Inhibitors of the Na+-glucose cotransporter SGLT2 enhance urinary glucose and urate excretion and lower plasma urate levels. The mechanisms remain unclear, but a role for enhanced glucose in the tubular fluid, which may interact with tubular urate transporters, such as the glucose transporter GLUT9 or the urate transporter URAT1, has been proposed. Studies were performed in nondiabetic mice treated with the SGLT2 inhibitor canagliflozin and in gene-targeted mice lacking the urate transporter Glut9 in the tubule or in mice with whole body knockout of Sglt2, Sglt1, or Urat1. Renal urate handling was assessed by analysis of urate in spontaneous plasma and urine samples and normalization to creatinine concentrations or by renal clearance studies with assessment of glomerular filtration rate by FITC-sinistrin. The experiments confirmed the contribution of URAT1 and GLUT9 to renal urate reabsorption, showing a greater contribution of the latter and additive effects. Genetic and pharmacological inhibition of SGLT2 enhanced fractional renal urate excretion (FE-urate), indicating that a direct effect of the SGLT2 inhibitor on urate transporters is not absolutely necessary. Consistent with a proposed role of increased luminal glucose delivery, the absence of Sglt1, which by itself had no effect on FE-urate, enhanced the glycosuric and uricosuric effects of the SGLT2 inhibitor. The SGLT2 inhibitor enhanced renal mRNA expression of Glut9 in wild-type mice, but tubular GLUT9 seemed dispensable for the increase in FE-urate in response to canagliflozin. First evidence is presented that URAT1 is required for the acute uricosuric effect of the SGLT2 inhibitor in mice.

Plasma urate, lung function and chronic obstructive pulmonary disease: a Mendelian randomisation study in 114 979 individuals from the general population

BackgroundUrate is a strong antioxidant in plasma and may protect against lung function impairment. We tested the hypothesis that high plasma urate is causally associated with better lung function and low risk of respiratory symptoms and COPD.MethodsWe measured lung function and plasma urate in 114 979 individuals from the Copenhagen City Heart Study and the Copenhagen General Population Study and genotyped for SLC2A9 rs7442295 and ABCG2 rs2231142 variants, previously associated with high plasma urate, in 110 152 individuals.ResultsIn the two studies combined, multivariable-adjusted 100 µmol/L higher plasma urate was associated with −1.54% (95% CI −1.67 to −1.40) lower FEV1 % predicted and −1.57% (95% CI −1.69 to −1.44) lower FVC % predicted observationally; the corresponding estimates for genetically determined 100 µmol/L higher plasma urate were −0.46% (95% CI −1.17 to 0.25) and −0.40% (95% CI −1.03 to 0.23). High plasma urate was also associated with higher risk of respiratory symptoms; however, genetically determined high plasma urate was not associated with respiratory symptoms. Finally, we identified 14 151 individuals with COPD and found ORs of 1.08 (95% CI 1.06 to 1.11) for COPD observationally and 1.01 (95% CI 0.88 to 1.15) genetically per 100 µmol/L higher plasma urate.ConclusionHigh plasma urate was associated with worse lung function and higher risk of respiratory symptoms and COPD in observational analyses; however, genetically high plasma urate was not associated with any of these outcomes. Thus, our data do not support a direct causal relationship.

Plasma Urate, Cancer Incidence, and All-Cause Mortality: A Mendelian Randomization Study

BACKGROUND Observationally, high plasma urate is associated with high risk of cancer. We used a Mendelian randomization design to test the hypothesis that high concentrations of plasma urate are associated with high cancer incidence and all-cause mortality observationally and genetically. METHODS We performed observational and genetic analyses using plasma urate and the urate solute carrier family 2 member 9 (SLC2A9) rs7442295 genotype in 86210 individuals from the Copenhagen General Population Study. Cancer and mortality end points were from national cancer and death registries. Incidences and risk of cancer and all-cause mortality were calculated using Cox regression, Fine and Gray competing-risks regression, and instrumental variable analyses. RESULTS During a median follow-up time of 3.9 years for cancer and 4.9 years for all-cause mortality, 3243 individuals received a diagnosis of cancer and 3978 died. Observationally, 50% higher plasma urate was associated with multivariable-adjusted hazard ratios of 1.11 (95% CI, 1.05–1.18) for cancer incidence and 1.07 (1.01–1.13) for all-cause mortality. Each A-allele of the SLC2A9 rs7442295 was associated with 9% higher plasma urate and hazard ratios of 1.07 (1.01–1.14) for cancer incidence and 1.07 (1.02–1.13) for all-cause mortality. In instrumental variable analyses, the odds ratios for a genetically determined 50% higher plasma urate was 1.22 (1.02–1.47) for cancer incidence and 1.49 (1.13–1.93) for all-cause mortality. CONCLUSIONS High plasma urate was both observationally and genetically associated with high cancer incidence and high all-cause mortality, suggesting causal relationships.