An LC-MS/MS- and hURAT1 cell-based approach for screening of uricosuric agents

Urate anion exchanger 1 (URAT1) expressed in the proximal renal tubules is responsible for about 90% of the reabsorption of uric acid. URAT1 is identified as an important target of uricosuric drugs. Here we present an LC-MS/MS-based approach, combined with URAT1-transgenic MDCK cells, for the assessment of uric acid. Cell lysis was executed with 50 mM NaOH to release uric acid. 1,3-¹⁵N₂ uric acid was employed as the internal standard. The harvested uric acid, along with the stable isotope-labeled uric acid, was analyzed by LC-MS/MS in multiple reactions monitoring and negative modes. Validation, i.e. determination of selectivity, precision, accuracy, extraction recovery, and matrix effect, and feasibility was evaluated by use of the approach developed. The linearity was observed in the range of 1.0-250 μM (r = 0.9960) with limit of detection of 50 nM and limit of quantitation of 200 nM. The precision and accuracy were found to be RSD ≤ 20% and 80-120% of the nominal value, respectively. Uric acid uptake showed concentration and time dependency in URAT1-transgenic cells. The observed inhibitory effects of three URAT1-targeted uricosuric drugs were consistent with those reported in literature. The stable isotope dilution-based approach was proven to be selective, sensitive, and convenient, which is a good in vitro model for URAT1-targeted drug candidate screening.