Human myeloperoxidase activity is inhibited in vitro by quercetin. Comparison with three related compounds.

Quercetin is an effective inhibitor of human myeloperoxidase (MPO) activity, both with purified enzyme (IC50 = 3.5 microM) and in a system using stimulated human neutrophils. Quercetin is significantly more potent than three other related compounds (rutin, rutin sulfate and troxerutin) and than methimazole, a previously-known myeloperoxidase inhibitor. The inhibitory activity of quercetin is of the competitive type. Moreover, quercetin is directly able to scavenge hypochlorous acid (HOCl), a chlorinated species generated by the MPO/H2O2/Cl- system.

[Modification of the antiradical defense system of the organism under the influence of the administration of a leukocyte factor in the rabbit. Its relation to the increase of radioresistance by biostimulants]. / Modification du système de défense antiradicalaire de l'organisme sous l'influence de l'administration d'un facteur leucocytaire chez le lapin. Ses rapports avec l'accroissement de la radiorésistance par les biostimulants.

Injection in the rabbit of the leucocyte endogenous mediator (LEM) liberated by activated granulocytes provokes after 24 h an increase in the glutathione concentration, particularly in the spleen and in the kidney, as well as an increase in acute phase proteins and modifications of the zinc concentration in the plasma, the liver and the kidney. These modifications are compared with those provoked by non specific biostimulants which increase the radioresistance during periods varying from several days to several weeks. It may be that LEM or a component accompanying it in the injected fraction is a factor intervening in the increase in radioresistance caused by biostimulants.