Kinetics of inhibition of peroxidase activity of myeloperoxidase by quercetin

Abstract

The inhibition of myeloperoxidase (MPO), isolated from human neutrophils, by quercetin was investigated by following peroxidase activity of the enzyme using o-dianisidine as the substrate. The inhibition parameters (IC 50 ) were obtained by graphical analysis of the inhibition curves. A reaction mechanism, which involved the enzyme inhibition by quercetin and H 2 O 2 in excess, was proposed. The rate and equilibrium constants for the proposed reaction path were calculated from experimental data. Kinetic analysis in noninhibiting H 2 O 2 concentration range in the absence and the presence of quercetin revealed that the reaction mechanism underwent Michaelis-Menten kinetics. K app,H 2 O 2 m and V app max values indicated that quercetin was a mixed inhibitor of MPO activity. The initial reaction rates were recalculated using the obtained results. Calculated curves fitted the experimental results within the range of experimental error.

Polyphenols from Silybum marianum inhibit in vitro the oxidant response of equine neutrophils and myeloperoxidase activity

“…Later, Momić et al . () and Shiba et al . () used docking simulations to suggest a tight binding of quercetin to MPO.…”

“…MPO is considered an inflammatory marker and the release of its active form, as evidenced in laminar tissues of horse with laminitis (Riggs et al, 2007), could involve the formation of strong oxidant species such as HOCl and NO 2 Á produced, respectively, by the chlorination and peroxidase activity of MPO, hence the interest in finding reversible inhibitors of MPO. While the inhibition of human MPO by taxifolin and quercetin is well characterized, there have been no previous studies into the inhibition of the enzyme by silybin and DHSB (Momi c et al, 2008;Kostyuk et al, 2003;Long et al, 1981). Likewise, the effects of these compounds on equine MPO remained to be explored.…”

“…() showed that quercetin inhibits human MPO with a Ki of 3.5 μ m and Momić et al . (, ) unravelled the mechanism by which quercetin interacts and inhibits human MPO. It has been shown that taxifolin, an analogue of quercetin also found in silymarin, had a comparable inhibitory effect on MPO activity (Kostyuk et al ., ; Shiba et al ., ), but very little work has been performed on silymarin's other components such as silybin and DHSB.…”

Automatic Identification of Myeloperoxidase Natural Inhibitors in Plant Extracts

“…Many non-steroidal anti-inflammatory drugs, anilines and phenols reversibly inhibit MPO. Anti-inflammatory drugs described as inhibitors of this enzyme have, in their structure, phenols or similar structures, which led us to further investigate these compounds’ ability to inhibit MPO [ 16 , 17 ]. These compounds could suppress ROS/RNS formation through the inhibition of certain enzymes, or metal-chelating compounds involved in the formation of free radicals.…”

Morphine, a potential inhibitor of myeloperoxidase activity

“…The antioxidant action of morphine has been compared to the one of antioxidant reference molecules, having already demonstrated their ability to interact with MPO (quercetin, gallic acid and ascorbic acid (Fig. 2)) [14,[33][34][35][36][37]. First, the potential anti-catalytic property of morphine was tested on MPO with SIEFED, Specific Immunological Extraction Followed by Enzyme Detection, an immunological technique able to measure specifically the MPO activity after exposure to potential inhibitors [37,38].…”