Structure-activity relationship of flavonoids with superoxide scavenging activity

The superoxide scavenging activities of 12 flavonoids were measured. The superoxide anions were generated by a hypoxanthine-xanthine oxidase system and measured by the nitrite method. The results showed that the scavenging ability enhanced with an increasing number of hydroxyl groups in rings B. Substitution at C3 position with a hydroxyl group increased the activity. Compared to a methoxyl group or a glycoside in this position, a free hydroxyl group showed the highest activity. A saturated C2−C3 bond showed a higher activity than a unsaturated bond. The absence of a carbonyl group at C4 position increased the activity.     

In vitro antioxidant profile of phenolic acid derivatives

Several caffeic acid esters isolated from propolis exhibit interesting antioxidant properties, but their in vivo use is compromised by hydrolysis of the ester bond in the gastrointestinal tract. Therefore, a series of caffeic acid amides were synthesized and their in vitro antioxidant profile was determined. A series of hydroxybenzoic acids, hydroxycinnamic acids, and the synthesized caffeic acid amides were tested for both their 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging and microsomal lipid peroxidation-inhibiting activity. Some of the highly active antioxidants were further tested by means of electron paramagnetic resonance for their hydroxyl radical scavenging activity. Since a promising antioxidant compound should show a lipid peroxidation-inhibiting activity at micromolar level and a low cytotoxicity, the cytotoxicity of the phenolic compounds was also studied. In all the assays used, the caffeic acid anilides and the caffeic acid dopamine amide showed an interesting antioxidant activity.     

In Vitro Antioxidant Profile of Phenolic Acid Derivatives

Several caffeic acid esters isolated from propolis exhibit interesting antioxidant properties, but their in vivo use is compromised by hydrolysis of the ester bond in the gastrointestinal tract. Therefore, a series of caffeic acid amides were synthesized and their in vitro antioxidant profile was determined. A series of hydroxybenzoic acids, hydroxycinnamic acids, and the synthesized caffeic acid amides were tested for both their 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging and microsomal lipid peroxidation-inhibiting activity. Some of the highly active antioxidants were further tested by means of electron paramagnetic resonance for their hydroxyl radical scavenging activity. Since a promising antioxidant compound should show a lipid peroxidation-inhibiting activity at micromolar level and a low cytotoxicity, the cytotoxicity of the phenolic compounds was also studied. In all the assays used, the caffeic acid anilides and the caffeic acid dopamine amide showed an interesting antioxidant activity.     

Supplementation of calves with stabilized orthosilicic acid

The bioavailability of silicon in stabilized orthosilicic acid was investigated in a double blind, placebo controlled supplementation study of calves maintained on a normal diet. The total dietary Si intake was increased by 4.9% in the form of stabilized orthosilicic acid. After 23 wk of Si supplementation, the serum Si concentration increased (p=0.0001,n=29) by 70% compared to control animals in spite of the low Si dose administered and the Si adequate diet. The individually administered Si dose was significantly associated with the serum Si concentration (r=0.44,p=0.016,n=29). The collagen concentration in dermis was significantly higher (p=0.019,n=4) in the Si group and a positive correlation (r=0.72,p=0.018,n=9) was found between the Si concentration in serum and the collagen concentration in cartilage. The calcium (Ca) and phosphorus (P) concentrations in serum were marginally higher for animals supplemented with Si compared to control animals. In serum, a significant linear relationship was found between the Si and the Ca concentration (r=0.31,p=0.019,n=59), whereas the magnesium concentration correlated marginally with the Si concentration (r=0.25,p=0.068,n=59). In summary, increasing the total dietary Si intake by 4.9% in the form of stabilized orthosilicic acid resulted in a 70% higher Si concentration in serum indicating a high bioavailability of Si in this supplement. The positive correlation between the serum Si concentration and the collagen concentration in cartilage and the serum Ca concentration, respectively, suggest the involvement of Si both in the formation of extracellular matrix components and in Ca metabolism.