PB0848 - Characterization of the uric acid transporter URAT1 (SLC22A12) in platelets and megakaryocytes

Background: URAT1, encoded by the SLC22A12 gene in humans, acts as an organic anion transporter that plays a key role in uric acid and oxidative homeostasis. High levels of uric acid lead to urate crystals formation in the joints or in urine resulting in gouty arthritis or kidney stones, respectively. Less well-known, the epidemiological association of hyperuricemia with adverse cardiovascular events poses the question of the contribution of high uric acid circulating levels to platelet reactivity and thrombosis.

Aims: To characterize URAT1 expression and function in human platelets and megakaryocytes.

Methods: URAT1 expression was verified by immunoblotting and by flow cytometry using independent antibodies in platelets and the megakaryocytic cell line MEG-01, with HEK293 as positive controls. Platelet aggregation in response to classical platelet agonists (collagen, arachidonic acid, ADP and thrombin receptor activating peptide (TRAP)), in the presence or absence of pharmacological URAT1 inhibitors (lesinurad and verinurad) was verified by light transmission aggregometry in washed platelets prepared from whole blood of healthy male and female volunteers.

Results: URAT1 immunoreactivity was detected on the surface of and within platelets and MEG-01 cells, at the expected molecular weight of 65 kD. Cell fractionation experiments were consistent with flow cytometry results. Incubation of washed platelets with uric acid (50-100 µg/ml) did not induce spontaneous platelet aggregation, nor did it induce synergistic effects in the presence of low concentrations of classical platelet agonists. However, collagen-, arachidonic acid-, ADP-, and to a lesser extent TRAP-induced platelet aggregation was inhibited by pre-incubation of washed platelets with either lesinurad (IC50 125 nM - 1.6 µM) or verinurad (IC50 145 nM - 14 µM).

Conclusion(s): Human platelets and megakaryocytes express the URAT1 transporter. Whether platelets and megakaryocytes can sense and respond to uric acid fluctuations in their environment remains uncertain and merits further investigation.