INTRODUCTION: Fetuin-A or α2-Heremans-Schmid glycoprotein (AHSG) is a hepatically synthesised negative acute phase plasma protein belonging to the cystatin superfamily of cysteine protease inhibitors. It acts as a potent inhibitor of vascular calcification (Schafer et al., 2003). Sub-physiological levels of serum fetuin-A are found in patients with chronic kidney disease (CKD) and is associated consequent ectopic vascular calcification (Ketteler et al., 2003). Patients with CKD also have a pro-oxidant milieu which contributes significantly to associated morbidity and mortality. AIM: The aim of this study was to investigate the effects of fetuin-A at a range of physiological and sub-physiological concentrations on oxidant injury caused to renal epithelial cells by the pro-oxidant paraquat, which generates superoxide anions and thereby causes oxidant injury (Samai et al., 2007). METHODS: Confluent cultures of NRK-52E cells, a rat proximal tubular cell-line, were incubated with increasing concentrations of paraquat (0-5 mM) in Dulbecco’s Modified Eagle’s Medium (DMEM) for 24 hours. Cultures were also incubated with fetuin-A (0.01, 0.1 and 1.0 mg/mL) for either 24 hours prior to (pre-incubations) or at the same time as paraquat (co-incubations). Cell viability was assessed via spectrophotometric measurement of the mitochondrial-dependent conversion of 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) into formazan. Data are presented as mean % cell viability±S.D., analysed using one-way ANOVA and Bonferroni’s post-testing. RESULTS: Paraquat (PQ) produced a significant reduction in the viability of NRK-52E cells at a concentration of 3 mM (untreated cells: 100.0±3.5% vs. PQ only: 15.9±7.7%, p<0.05, n=6). Co-incubation with fetuin-A at a physiological concentration (1 mg/mL) and paraquat (3 mM) for 24 hours produced a significant reduction in paraquat toxicity (PQ only: 15.9±7.7% vs. PQ+fetuin-A: 33.8±6.2%, p<0.05, n=6). Pre-incubation with fetuin-A (1 mg/mL) for 24 hours also produced a reduction in paraquat toxicity (PQ only: 15.9±7.7% vs. fetuin-A then PQ: 67.5±7.1%, p<0.05, n=6). Pre-incubation with fetuin-A produced a greater effect than co-incubation. A sub-physiological concentration of fetuin-A (0.1 mg/mL) was also able to protect against paraquat toxicity following pre-incubation (PQ only: 15.9±7.7% vs. fetuin-A then PQ: 46.44±.7%, p<0.05, n=6). CONCLUSIONS: These results suggest that physiological and sub-physiological concentrations of fetuin-A can provide significant protection against oxidant injury. Our results demonstrate that pre-incubation is significantly more protective than co-incubation. The cellular mechanisms underlying this renoprotection warrant further investigation.