Abstract
Objective Caffeine, an adenosine receptor antagonist, is a potent central nervous system stimulant that also impairs insulin signaling. Recent studies have suggested that coffee consumption lowers serum urate (SU) and protects against gout, by unknown mechanisms. We hypothesized that caffeine lowers serum urate by affecting activity of urate transporters. Methods We examined the effect of caffeine and adenosine on basal and insulin‐stimulation of net 14 C‐urate uptake in the human renal proximal tubule cell line PTC‐05, and on individual urate transporters expressed in Xenopus laevis oocytes. Results We found that caffeine and adenosine efficiently inhibited both basal and insulin‐stimulation of net 14 C‐urate uptake mediated by endogenous urate transporters in PTC‐05 cells. In oocytes expressing individual urate transporters, caffeine (>0.2 mM) more efficiently inhibited the basal urate transport activity of GLUT9 isoforms, OAT4, OAT1, OAT3, NPT1, ABCG2 and ABCC4 than did adenosine, without significantly affecting URAT1 and OAT10. However, unlike adenosine, caffeine at lower concentrations (<0.2 mM), very effectively inhibited insulin‐activation of urate transport activity of GLUT9, OAT10, OAT1, OAT3, NPT1, ABCG2 and ABCC4 by blocking activation of Akt and ERK. Conclusions We postulate that inhibition of urate transport activity of the reabsorptive transporters GLUT9, OAT10, and OAT4 by caffeine is a key mechanism in its urate‐lowering effects. Additionally, the ability of caffeine to block insulin‐activated urate transport by GLUT9a and OAT10 suggests greater relative inhibition of these transporters in hyperinsulinemia.