Unexpected effect of urate on hydrogen peroxide-induced oxidative damage in embryonic chicken cardiac cells

Uric acid (UA) is a potent scavenger of oxidants in most mammalian and avian species. The aim of this study was to obtain more comprehensive information regarding the relationship between different concentrations of UA and oxidative balance in chicken cardiac cells. First, oxidative damage parameters were measured in chicken cardiac cells treated with different concentrations of UA. UA concentrations within the normal physiological range had no effect, while treatment with a high level of UA, i.e. 1200 μM, increased the malondialdehyde (MDA) and protein carbonyl contents, decreased the superoxide dismutase (SOD) and catalase (CAT) activities, and had no effect on glutathione (GSH) in cardiac muscle cells. In addition, the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway was stimulated in cells treated with 1200 μM UA. Next, the role of UA in protecting cells from oxidative damage was investigated in hydrogen peroxide (H₂O₂)-damaged chicken cardiac cells. Treatment with UA within the normal physiological range reduced the increased MDA and protein carbonyl contents and SOD enzymatic activity induced by H₂O₂ exposure to some extent and inhibited reactive oxygen species (ROS) formation, presumably as a result of the Nrf2 pathway activation in H₂O₂-damaged cells. By contrast, the MDA and protein carbonyl contents were increased, SOD enzymatic activity was depressed, and the Nrf2 pathway was further down-regulated in H₂O₂-damaged cells treated with 1200 μM UA. In conclusion, the results indicated that physiological UA concentration partially alleviated oxidative stress in chicken cardiac muscle cells treated with H₂O₂. However, supraphysiological UA concentrations promoted oxidative damages directly in primary cultured chicken cardiac muscle cells and aggravated oxidative stress in H₂O₂-damaged cells.