Superoxide Radical Scavenging Capacity Research Articles

Superoxide scavenging by polyphenols: effect of conjugation and dimerization

The superoxide anion scavenging capacity of two flavonols (quercetin and kaempferol) and some of their conjugates (quercetin-3-rhamnoglucoside, quercetin-3-sophoroside, quercetin-3-sulphate, quercetin-3-glucuronide, kaempferol-3-sophoroside, kaempferol-3-glucuronide) and of several hydroxycinnamic acids (caffeic acid, ferulic acid, 5-5 diferulic acid, 8-O-4 diferulic acid and 8-8 diferulic acid) were studied. Superoxide anions were generated non-enzymatically in a phenazine methosulphate-NADH system and assayed by reduction of nitro-blue tetrazolium. Among the flavonols examined, the most effective scavengers of superoxide anions were the sophoroside, glucuronide and rhamnoglucoside conjugates. Conversely, quercetin-3-sulphate and the flavonol aglycones, exhibited some pro-oxidant activity at the range of concentrations tested (0.5-10 μM). These results show that conjugation has a marked effect on the scavenging capacity of flavonols and that the type of conjugate at the 3-position determines the final superoxide scavenging capacity. Caffeic acid and ferulic acid showed no effect on the generation of superoxide anions by phenazine methosulphate-NADH. However, dimerization of ferulic acid enhanced the superoxide scavenging capacity of this hydroxycinnamic acid, but this depended on the type of linkage between the monomers. The order, from highest to lowest, of superoxide radical scavenging capacity for the dimers of ferulic acid was: 5-5-diferulic acid > 8-O-4-diferulic acid > 8-8-diferulic acid.

Experimental Study Showing a Diminished Cytosolic Antioxidative Capacity in Kidneys of Aged Rats

In response to the rising demand for renal transplantations, more and more marginal (e.g. older) organs are being transplanted with the result of decreasing graft survival rates. Ischemia-reperfusion injury via oxidative stress is thought to be the main pathogenetic factor for this phenomenon. The cytosolic antioxidative capacity (CAC; expressed as superoxide anion radical scavenging capacity and quantified as the amount of cytosol (=ID₅₀), which scavenges 50% of superoxide anions generated by a defined xanthine oxidase activity in vitro) and the catalase activity were therefore quantified in renal tissues of young (10 weeks) and older (40 and 60 weeks) Wistar rats and compared to each other. CAC with an ID₅₀ of 0.064 μl in 10-week-old rats was significantly higher than in older rats (0.152 μl in 40- and 0.100 μl in 60-week-old rats; p < 0.01). The catalase activity in 10-week-old rats was 18,200 ± 3,500 U/g w/w and 18,900 ± 850 U/g w/w in 40-week-old rats. In 60-week-old rats, however, catalase activity was found to be significantly less (7,500 ± 175 U/g w/w; p < 0.01). In conclusion, the aforementioned significant decrease of the cytosolic antioxidative capacity of kidneys in older rats should be the rationale for extensive cytoprotective, antioxidative treatment trials especially after renal transplantation from aged donors.