ATP-binding cassette transporter G2 (ABCG2), also known as
breast cancer resistance
protein (BCRP), is identified as a high-capacity
urate exporter and its dysfunction has an association with serum
uric acid (SUA) levels and
gout/
hyperuricemia risk. However, pathophysiologically important pathway(s) responsible for the ABCG2-mediated
urate excretion were unknown. In this study, we investigated how ABCG2 dysfunction affected the
urate excretion pathways. First, we revealed that mouse Abcg2 mediates
urate transport using the membrane vesicle system. The export process by mouse Abcg2 was
ATP-dependent and not saturable under the physiological concentration of
urate. Then, we characterized the excretion of
urate into urine, bile, and intestinal lumen using in vivo mouse model. SUA of Abcg2-knockout mice was significantly higher than that of control mice. Under this condition, the renal
urate excretion was increased in Abcg2-knockout mice, whereas the
urate excretion from the intestine was decreased to less than a half. Biliary
urate excretion showed no significant difference regardless of Abcg2 genotype. From these results, we estimated the relative contribution of each pathway to total
urate excretion; in wild-type mice, the renal excretion pathway contributes approximately two-thirds, the intestinal excretion pathway contributes one-third of the total
urate excretion, and the
urate excretion into bile is minor. Decreased intestinal excretion could account for the increased SUA of Abcg2-knockout mice. Thus, ABCG2 is suggested to have an important role in extra-renal
urate excretion, especially in intestinal excretion. Accordingly, increased SUA in patients with ABCG2 dysfunction could be explained by the decreased excretion of
urate from the intestine.