Exercise-induced changes in renal URAT1 activity and expression in rats

Exercise serum regulates uric acid transporters in normal rat kidney cells

Hyperuricemia (HUA) refers to a physiological condition of high serum uric acid (SUA) level in the body, which may cause an increased risk of several chronic diseases. The kidney's impaired uric acid (UA) metabolism is an important reason for HUA. In this study, we tested the hypothesis that circulating factors produced during exercise regulate the expression of ABCC4, ABCG2, URAT1, and GLUT9 in normal rat kidneys and normal rat kidney cells (NRK-52E) and their relationship with NF-κB and NRF-2. NRK-52E cells were separately cultured by serum from 10 healthy SD rats who did not exercise (CON) and 10 healthy SD rats who did aerobic treadmill exercise for 6 weeks. Cells cultured by serum from rats who did aerobic treadmill exercise for 6 weeks were separated by without NRF-2 inhibitor (EXE) and with NRF-2 inhibitor (EXE + ML). SUA level of rats was tested by using dry chemical assays, xanthine oxidase (XOD) activity in serum and liver were tested by using enzyme colorimetry assays, protein expression in kidney and NRK-52E cells were tested by using Western-blot, and UA levels in the upper or lower chamber were tested by colorimetry assays. Aerobic exercise reduced SUA levels in rats but did not significantly affect on liver xanthine oxidase. It also increased the expression of some UA transporters in the kidney and NRK-52E cells and increased the cells' ability in UA excretion. When the NRF-2 was inhibited, the NF-κB and ABCG2 increased, and the expression of ABCC4, URAT1, and GLUT9 decreased. In conclusion, this study suggested that 6 weeks of aerobic treadmill exercise intervention may help to improve the excretion of UA in renal cells, suggesting that long-term aerobic exercise may be a means to prevent hyperuricemia.

Delayed uric Acid accumulation in plasma provides additional anti-oxidant protection against iron-triggered oxidative stress after a wingate test

Reactive oxygen species are produced during anaerobic exercise mostly by Fe ions released into plasma and endothelial/muscle xanthine oxidase activation that generates uric acid (UA) as the endpoint metabolite. Paradoxically, UA is considered a major antioxidant by virtue of being able to chelate pro-oxidative iron ions. This work aimed to evaluate the relationship between UA and plasma markers of oxidative stress following the exhaustive Wingate test. Plasma samples of 17 male undergraduate students were collected before, 5 and 60 min after maximal anaerobic effort for the measurement of total iron, haem iron, UA, ferric-reducing antioxidant activity in plasma (FRAP), and malondialdehyde (MDA, biomarker of lipoperoxidation). Iron and FRAP showed similar kinetics in plasma, demonstrating an adequate pro-/antioxidant balance immediately after exercise and during the recovery period (5-60 min). Slight variations of haem iron concentrations did not support a relevant contribution of rhabdomyolysis or haemolysis for iron overload following exercise. UA concentration did not vary immediately after exercise but rather increased 29% during the recovery period. Unaltered MDA levels were concomitantly measured. We propose that delayed UA accumulation in plasma is an auxiliary antioxidant response to post-exercise (iron-mediated) oxidative stress, and the high correlation between total UA and FRAP in plasma (R-Square = 0.636; p = 0.00582) supports this hypothesis.