Perfecting a high hypoxanthine phosphoribosyltransferase activity–uricase KO mice to test the effects of purine‐ and non‐purine‐type xanthine dehydrogenase (XDH) inhibitors
Takuji Hosoya, Shunya Uchida, Shigeru Shibata, Naoko H. Tomioka, Makoto Hosoyamada
Abstract
BACKGROUND AND PURPOSE: Purine metabolism in mice and human differ in terms of uricase (Uox) activity as well as hypoxanthine phosphoribosyltransferase (HPRT) activity. The aim of this study was the establishment of high HPRT activity-Uox knockout (KO) mice as a novel hyperuricaemic model. Then to investigate the effects of purine-type xanthine dehydrogenase (XDH) inhibitor, allopurinol, and non-purine-type XDH inhibitor, topiroxostat, on purine metabolism. EXPERIMENTAL APPROACH: mice with uricase KO mice. The pharmacological effects of allopurinol and topiroxostat were explored by evaluating urate, hypoxanthine, xanthine and creatinine in the plasma and urine of these model mice. Furthermore, we analysed the effect of both drugs on erythrocyte hypoxanthine phosphoribosyltransferase activity. KEY RESULTS: for 7 days. The urate-lowering effect was equivalent for allopurinol and topiroxostat. However, the urinary hypoxanthine/creatinine ratio and xanthine/creatinine ratio after treatment with topiroxostat were significantly lower than for allopurinol. In addition, the urinary oxypurine/creatinine ratio was significantly lowered after treatment with topiroxostat, but allopurinol elicited no such effect. Furthermore, allopurinol inhibited mouse erythrocyte hypoxanthine phosphoribosyltransferase, while topiroxostat did not. CONCLUSIONS AND IMPLICATIONS: High hypoxanthine phosphoribosyltransferase activity- uricase KO mice were established as a novel hyperuricaemic animal model. In addition, topiroxostat, a non-purine-type xanthine dehydrogenase inhibitor, elicited a potent plasma urate-lowering effect. However, unlike allopurinol, topiroxostat did not perturb the salvage pathway, resulting in lowered total oxypurine excretion.