Hypochlorous acid (HOCl), the main product of the myeloperoxidase system, is a strong oxidant and a potent chlorinating agent, which can damage host tissues. In the present work, the scavenger effect of three aglycone flavonols (myricetin, quercetin and kaempferol) and of the natural glycoside flavonol, rutin, was studied towards HOCl using luminol-dependent chemiluminescence (CL). At 1 micro mol/L fi nal concentration, rutin was the most powerful scavenger of HOCl with an inhibitory luminol oxidation of 91.4% +/- 3.2%. Quercetin, kaempferol and myricetin inhibited the luminol-dependent CL at the same concentration only by 75.9% +/- 3.4%, 57.7% +/- 5.3% and 43.3% +/- 3.5%, respectively. With increasing concentration of these flavonols, a dose-dependent inhibition of luminol CL was observed. In order to prove to what extent flavonols scavenge HOCl, their concentrations that gave 50% inhibition of luminescence (IC50) were compared to IC50 values of the sulphur-containing compounds N-acetyl cysteine (NAC) and taurine. The scavenging activities of compounds tested decrease in the order: rutin > NAC > quercetin > kaempferol > taurine. The present study revealed that rutin was the most effective scavenger agent.

The antioxidative activity of Cleome arabica L. leaf extract was studied toward superoxide anion radical generating systems. The extract at 10 mg=ml has no scavenger effect on superoxide anion radicals generated by the xanthine-xanthine oxidase system, as determined by either the reduction of cytochrome c or pholasin luminescence. Also, this extract, up to 50 mg=ml, did not affect the uric acid production by xanthine oxidase. However, the extract showed a great inhibition activity, in a dose-dependent manner, of neutrophil pholasin luminescence stimulated by formyl-methionyl-leucylphenylalanine (fMLP). Indeed, the inhibition of pholasin luminescence was 80.22 AE 2.9%, 90.22 AE 4.0%, and 101.0 AE 1.0% in presence of the extract at concentrations of 1, 2, and 10 mg=ml, respectively. Thereby, it is likely that Cleome arabica leaf extract showed an inhibitory effect on enzyme(s) involved in signaling pathways of fMLP-stimulated neutrophils. Effectively, the extract exerted a significant inhibitory effect (p < 0.05), in a dose-dependent manner, on elastase release by fMLP/ cytochalasin B-stimulated neutrophils.

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