Amino acids of importance for the antioxidant activity of human serum albumin as revealed by recombinant mutants and genetic variants.

AIMS: To determine molecular information about the antioxidant properties of human serum albumin, which is an important extracellular antioxidant. To obtain this information, we studied this function of the protein by using H2O2 as the representative reactive oxygen species and two recombinant mutants and ten genetic variants with single-residue mutations. MAIN METHODS: The antioxidant capabilities of the isoforms were registered as their ability to diminish the H2O2-induced conversion of dihydrorhodamine 123 to rhodamine 123, which can emit fluorescence at 536 nm. Structural properties were examined by circular dichroism and SDS-PAGE. KEY FINDINGS: Cysteine residues are important for the antioxidant function, but their effect depends on their position in the protein, with Cys410 > Cys34 ~ Cys169 (when not involved in forming a disulfide bond). Likewise, the substitution of a glutamic acid at position 122 or 541, but not at 240 or 560, improves the antioxidant effect, perhaps by making the methionine residues in their vicinity, Met123 and Met548, respectively, more accessible for the oxidant. A lysine at position 505, but not at 82 or 570, decreases the oxidative effect. Finally, the mutations D269G and K276N had no effect. In certain cases, albumin acts as a sacrificial antioxidant, as in the case of the mutants C34S and, in particular, R410C and E505K. SIGNIFICANCE: The information gained is of protein chemical relevance, but it may also be helpful in understanding the function of proteins that act as antioxidants in biological systems subjected to oxidative stress in conditions such as inflammation and aging.

Effect of intravenous iron administration frequency on AOPP and inflammatory biomarkers in chronic hemodialysis patients: a pilot study.

OBJECTIVES: Intravenous iron administration (IVIR) is effective for correcting anemia in hemodialysis (HD) patients, but it also enhances the generation of hydroxyl radicals. Previously we demonstrated that IVIR increases oxidized serum albumin levels in HD patients. However, the effect of IVIR frequencies on the oxidative stress has never been studied before. Therefore, we compared the two IVIR schedules recommended by the Japanese Society for Dialysis Therapy guideline 2004 by measuring oxidized albumin in chronic HD patients. DESIGN AND METHODS: Twenty-two HD patients were divided into two IVIR protocol groups (group I: 40 mg of iron 3 times a week for 4 weeks, group II: 40 mg of iron once a week for 3 months). These protocols differ in IVIR frequency, but receive the same amount of iron (total 520 mg). We compared these two regimens by determining the levels of hemoglobin, serum ferritin, advanced oxidation protein products (AOPP), and oxidized albumin at 0, 4, 8, 12, 16, and 20 weeks. RESULTS: Both patient groups resulted in a similar and significant increase in hemoglobin levels, whereas group I markedly induced AOPP and oxidation of serum albumin than group II at 4 weeks (P<0.05). AOPP and oxidation of serum albumin was also gradually declined by 20 weeks, while the oxidized albumin and AOPP in group II was not significantly changed during the entire experimental period. Transferrin saturation and serum ferritin levels were also increased in group I compared with group II at 4 weeks (P<0.001). In addition, we found a strong positive correlation between oxidized albumin and serum ferritin levels (r=0.615, P<0.05), suggesting the possibility that the accumulation of iron stores has a causative role in the progression of oxidative stress in HD patients treated with IVIR. CONCLUSIONS: The results of this study indicate that lower frequency IVIR protocol is recommended to reduce IVIR-induced oxidative stress in HD patients.